Electric currents must always circulate in closed paths—that is, the current that starts out from a generator must return to it, and the amount coming back is the same as that which leaves. The action of an electric generator can be understood by comparing it with that of a water pump pumping into a pipe which runs around from the delivery end to the suction. With such an arrangement it can be seen that the action of the pump would be to keep the water in circulation, but the same water would be pumped through the pump and the pipe all the time. With an electric generator the action is the same, and in Fig. 22 the current flowing along any one of the tracks follows the course indicated by the arrows. The currents pass out to the several tracks through the trolley wires T T T T, and return through the tracks R R R R. The bus bar A is connected with a plate D, which is imbedded in the ground, and is also connected with the ends of the rails R R R R. Suppose for a moment that the two lower generators are out of service, their switches a a being turned so as to disconnect them from the bus A, and, further, suppose that the three lower b switches are open, so that the current can only pass to the upper track; then the top generator will feed into the top road only. Tracing the path of the current under these conditions, we find that it will start from the upper side of the generator through the a switch to the B bus, and thence to the trolley wire at the top of the figure. On reaching the first car a portion of the current passes to the track R, the amount being dependent upon the speed of the car and the load. Why the whole current does not follow this path generally puzzles the layman, but the explanation is that the motors hold the current back, and only allow as much to pass through them as is necessary to perform the required work—that is to say, the current flowing through each car is not controlled by the generator or by the force of the current, but by the requirements of the motors. The amount of current delivered by the generator is governed by the demands of the motors. The current that does not pass through the first car goes on to the second one, and if there were more cars there would be current left in the trolley wire to supply them. After passing through the motors of the two cars the current returns through the rails R to the plate D, and thus to bus A, from which it enters the lower side of the top generator. It will from this explanation be seen that the action of the generator is simply to keep the current circulating. If two of the generators are connected with the bus bars A and B, the current required by the motors will be delivered by the two machines, and if the three generators are placed in service the current will be divided among them.

When two or more generators are used, it is necessary to provide means to prevent the current from dividing unequally between them; if this were not done, one machine might do nearly all the work, while the other one would be practically idle. The means employed to accomplish the result is simply an additional bus bar, which is called an equalizing bus. We will not undertake to explain the principle upon which this arrangement acts; it is sufficient to say that by such means the work can be distributed in amounts directly proportional to the capacity of the generators, so that if one machine is very much larger than the others it will take a portion of the load corresponding to its size. In order that these results may be attained it is necessary to properly adjust the several generators, and as no machine can be made to work with the accuracy of perfection, the work will not be distributed in true proportion for all conditions of load; thus if the generators are adjusted so as to each take its proper share when all the cars are in operation, one machine may do too much or not enough when only one half the number are running, but the excess or deficiency will not be more than a few per cent unless the adjustment is very defective.

Electric generators for railway work are made in all sizes, from those only large enough to operate four or five cars to others capable of furnishing sufficient current for thirty or forty or even more. Small generators are made so as to be driven by a belt running over a pulley mounted on the end of the armature shaft, or they may be arranged to be connected to the end of a steam-engine shaft, and thus become what is called direct connected machines. Large generators are almost invariably of the latter type. A machine of this class is illustrated in Fig. 23. The driving engine is shown at E, the cylinder being in the background and the crank toward the front, the shaft being clearly seen at S, while F is the fly wheel. The generator is mounted directly upon the engine shaft, between the bearing at the crank end and the fly wheel. The large ring marked G is the field magnet ring, and at D D D the field coils are shown. These coils are equally spaced all the way around the circle. The commutator is marked C, and the commutator brushes are located at B B. The armature can not be seen very well, as it is covered by the brush holders and their supporting frames, but it is located within the ring G in the position designated by A. This machine is one of a number used to operate the roads of Troy, N. Y., and is of about one-thousand-horsepower capacity, which is enough to furnish all the current required to run sixty or seventy cars.

The switches a a and b b, shown in Fig. 22, and the bus bars A B, are mounted upon a large panel, made of marble or slate, called a switch board. These switches are sufficient for the purpose of turning the current on or off any track or for connecting and disconnecting the generators, but for the successful operation of the plant it is necessary to have other devices by means of which the strength of the current may be ascertained, and also the electro-motive force. It is necessary to provide each generator with means for varying the electro-motive force of the current it generates, otherwise the load could not be properly equalized between the several machines. All these different devices are located upon the switch board, so as to have them in an accessible position. A railway switch board, arranged for four generators and a large number of distributing circuits, is shown in Fig. 24. The four generator switches are shown at a a a a, and the circles marked R, directly under them, are the devices by means of which the electro-motive force of the current is regulated. These devices are called field regulators, from the fact that their office is to regulate the strength of the field magnets of the generators, making them stronger to increase the electro-motive force and weaker to reduce it. The part seen upon the front of the switch board is not the regulator proper, but only the handle and the contact points over which this swings. The instruments marked A A A A are for measuring the strength of the current of each individual generator, and are called ammeters. The instruments marked V V V V are for the purpose of indicating the electro-motive force of the currents of the several generators, and are called voltmeters. Ag is an ammeter used to measure the strength of the total current, and Vg is a voltmeter that indicates the electro-motive force of the current passing out to the cars on the various lines. The ammeter Ag is not an actual necessity, for the strength of the total current can be ascertained by adding the readings of the four instruments connected with the generators, but it is a convenience, as it saves the trouble of performing the addition. The voltmeter Vg, however, can not be regarded in this light; in fact, its presence is decidedly serviceable, for it indicates the average electro-motive force of all the generators; therefore if any one of the instruments V V V V is higher or lower it shows at once that the generator to which it is attached is out of adjustment and not doing its proper share of the work. The switches b b b, by means of which the current is turned on to the several external circuits, are shown at the extreme end of the switch board.

The instrument marked W, located between the a switches, is called a wattmeter, and its office is to indicate the amount of power furnished by the generators. This instrument is not always used, as it is a convenience but not a necessity. It can be seen at once that whether it is used or not, the amount of power required to operate the roads will be the same, but it is thought by most railroad managers that it is desirable, for then the relation between the coal consumed and the power developed can be seen; and if the showing is not as good as it should be, the engineer can remind the firemen that they are not exercising as much care in feeding the boilers as they should. Considered in this light, the watt-meter acts as a check to wastefulness on the part of the employees.

The instruments marked C C C C serve the same purpose in connection with the generators as the safety fuses do with respect to the car motors; they are electro-magnetic devices used to open the generator circuits whenever the current reaches a strength that is sufficient to injure the machine. These devices are called circuit breakers. As will be noticed, there are four located directly above the four a switches, and, at the farther end of the board, a large number located directly above the b switches. The latter act to open the individual circuits when the currents flowing in them become too strong, and the former are controlled entirely by the current of the generator circuits. A circuit breaker is more reliable than a safety fuse, because it acts quicker. With the fuse the current must act for some time before it can melt the metal, as a sufficient amount of heat can not be generated instantly. With the circuit breaker, however, the action is instantaneous, for as soon as the current reaches the predetermined strength the magnetism of the operative parts of the device becomes sufficiently strong to cause it to act. A circuit breaker is simply a switch that is arranged to be opened automatically by the action of a magnet, instead of by the hand of the operator. The switch part of the apparatus is held in place by a catch that is set much after the fashion of the catch in a mouse trap—that is, so that the least pressure will disengage it. A strong spring acts to throw the switch open, and as soon as the catch is tripped by the actuating magnet the force of the spring comes into action and the circuit is opened.

The circuit breaker is a very valuable apparatus, for it frequently happens that, through delays of one kind or another, a large number of cars concentrate at one point on the road, and, as all the motormen are anxious to make headway, they all start up at once at the first opportunity. If there were no circuit breakers at the power house the result would be that some of the generators would be greatly overloaded and perhaps disabled; but, owing to the presence of the circuit breakers, the actual result is that the circuit is broken, and then the motormen have to wait until the current is turned on again. If too many of them try to start their cars at the second trial the current will again stop. After two or three ineffectual efforts have been made to start all the cars together the motormen will conclude to go easy, and set a few in motion at a time. In this way the cars will become more evenly distributed along the line, and the demand for current at the point of blockade will reduce to the normal amount, or nearly so, and the running of the cars will continue without further interruption, for the current drawn by the motors having been reduced to the average amount, the circuit breaker will cease to act.

The bus bars and all the connections between them and the generators and external circuits, as well as with all the instruments, are located behind the switch board. All these connections are so secured that they can not come in contact with each other except where contacts are required; care is also taken to prevent any connection being made with the iron framing that supports the marble slabs. The front of a switch board is generally very attractive, the surface being of highly polished marble, while all the switches and instruments are finely finished and, as a rule, of decidedly ornamental design.

The switch board might be looked upon as the fountain head from which the entire operation of an electric railway system is controlled. By the movement of one set of switches upon it the generators are thrown in or out of service, and by the movement of another set of switches the several branches of the road are rendered active or inactive.

IS THE CHRISTIAN RELIGION DECLINING?
By the Rev. CHARLES AUGUSTUS BRIGGS, D. D.,
PROFESSOR OF BIBLICAL THEOLOGY, UNION THEOLOGICAL SEMINARY.

The question whether the Christian religion is declining is agitating the public mind in some measure at the present time. This is due to the many changes that are taking place in the forms of religion, the types of doctrine, and the methods of action in the numerous religious organizations which bear the name of Jesus Christ. Are these changes symptoms of disease and decay in the Christian religion, or are they evidences of renewed vitality and enlargement by growth? It is quite evident that many things which have been regarded as important and even essential in the past have declined in importance, and some of them seem to be on the eve of disappearing altogether. It is not surprising that those who have been trained to regard these as essential to Christianity should think that the Christian religion is declining with them. If, however, these things are not so important as has been supposed, but have gained for a time an exaggerated importance, then their decline to their normal position and the advance of other things to their rightful place, as more important things than has hitherto been supposed—all this is evidence of a healthful advance in Christianity. This question, therefore, will be answered in accordance with the point of view of the one who considers it. If it is to be answered correctly we must put aside all prejudice, and examine the whole situation candidly and with a critical scientific spirit. It is impracticable within the bounds of this article to examine this question on all sides. We can only make a few suggestions relating to it.

It is necessary at the outset to approach the question aright. We must distinguish between what is essential to the Christian religion and what is non-essential. This is not so easy a task as one might imagine. We can only make this distinction generally, and not with scientific precision. In the study of religions we have to distinguish (1) the more fundamental things in the historical institutions and experience in life; (2) the doctrines which express the popular belief or scientific knowledge of the adherents of the religion; and (3) the expression of the religion in ethical principles and moral conduct. The order of development is always life, doctrine, morals. The earlier stages of the Christian religion and of Christian experience at any time and in any community is the vital experience and the institutional organization. Doctrines of faith and knowledge presuppose the vital relation, and morals presuppose both, and conduct is the final aim and crown of the whole development. And yet there are some scholars who exaggerate the relative importance of each one of the three in its relation to the other two and to the whole.

In our age greater attention is given to Christian ethics and sociology than ever before. A man who has the ethical enthusiasm of our times is inclined to criticise historical Christianity with great severity, because of its failure to realize the highest ethical ideals, and especially those presented by Jesus in his teaching and his example. Historical Christianity is so far below these ideals, even in its best types, that one is inclined to say if the Church has failed so badly in nineteen centuries, what prospect has it in the present or the future? Some good men in our times are disgruntled with historical Christianity for its ethical failures, and keep aloof from the Church on that account; but these are after all proportionately few, and they are unreasonable, for they exaggerate the ethical phase of Christianity over against the doctrinal and the vital; they fail to see what is necessarily involved in the development of the Christian religion, that the ethical age should come last of all; and they also are not just in their estimate of Christian history, for, notwithstanding the failure of the Church, there has been a wonderful and steady ethical advance through the centuries. Indeed, it is Christianity itself which is chiefly responsible for the ethical enthusiasm of the present time, and this is an evidence that Christianity is about to enter upon the last and highest stage of its development. Holy love in principle and practice in the liberty of self-sacrifice is better understood in the Church to-day than ever before, and it is becoming more influential in the Church and in the world. The Church is about to put forth the supreme ethical influence of holy love to transform society and the lives of men.

In large sections of the Church the greatest stress is still laid upon Christian doctrine, especially as expressed in dogmatic forms. If a man thinks that orthodox doctrine is the test of a healthful and vigorous church, he will make that the determining element in his judgment whether Christianity is advancing or declining. In this sphere we have to distinguish three things: (1) The popular orthodoxy, which is determined by the consensus of teaching from the pulpit; (2) the scholarly orthodoxy, which is determined by the teaching of the theologian from the chairs of the theological schools and in text-books of dogmatic theology; (3) the official orthodoxy, which is determined by creeds, liturgies, confessions of faith, and canons of the Church.

There can be no doubt that there has been a great overturning of dogma in our times, and it is altogether probable that this will assume much greater dimensions. Many think that dogma has had an exaggerated importance in the past, and, from their point of view, the Christian religion has made an advance by pushing dogma back to a less dominant position. Those who maintain that dogma is of supreme importance naturally think that the Christian religion declines when dogma is discredited in the Christian community. There can be little doubt that a large number of men absent themselves from church attendance because they dislike the popular orthodoxy, which seems to them antiquated, unscientific, and untrue. Many refuse to unite with religious organizations which are dominated by an orthodoxy representing the theories of scholastic theology. Many remain apart from the churches because they are unwilling to be responsible in any way for their official orthodoxy. Many, born and trained in Presbyterian families, refuse to remain in an organization which is responsible for the hard doctrines set forth in the Westminster Confession. Many Methodists refuse to be compromised by Wesley’s doctrines and Wesley’s rules of life. Many refuse to remain Baptists because of what is involved in close communion. Many refuse to be Episcopalians because they resent the doctrines and practices of sacerdotalism. And so we could find, more or less in all religious communions, a dissatisfaction with dogmas—sometimes superficial, giving a plausible excuse for absence, sometimes profound, inciting active hostility to the Church. If all of these dissatisfied ones are to be regarded as hostile or indifferent to Christianity, then it is evident that an army of Christians have practically separated themselves from the Church in our time, and we must say that Christianity has in this respect declined. If, on the other hand, we think that these dissatisfied and disgruntled ones are yet Christians, and that they are maintaining their faith in Christ in opposition to an unreasonable church, that they are exerting an important influence in the transformation of the dogmas of the Church, then we may say that this is an evidence that Christianity is in a state of transition, that it is on the move away from an untenable position of exaggerated dogma to a truer and stronger position, in which dogma will be transformed and given its normal place and importance.

The effort to throw off the bondage of the popular and the scholastic dogma is an advance, and not a decline; it is an advance into the realm of freedom. It first gives the possibility of a critical re-examination of the dogmatic faith of the Church. Only by the application of the scientific methods of our age to dogma is it possible for our age to verify dogma and accept it as valid and reliable. We can not rely on anything that is merely traditional or the product of the logical analysis of premises which remain themselves unverified. The revolt against the confessional orthodoxy, especially in the Presbyterian, Reformed, and Lutheran Churches, is not a sign of decline, as some think, but a wholesome movement which indicates a determination to know the truth and to hold nothing but the truth.

The Chicago-Lambeth articles, adopted by the whole Anglican communion throughout the world, reduces the essential doctrines of Christ’s Church to the Nicene Creed and the Apostles’ Creed; those creeds in which all the great historical churches, the Greek and the Oriental, the Roman and the Protestant, agree. This marks a dogmatic advance, not a dogmatic decline, because it makes the distinction between the essential and unessential doctrines, it defines essential doctrines by holding up ancient fundamental historical creeds; it thereby represents all other matters as within the realm of the unessential doctrines, the province of Christian liberty.

The churches are therefore readjusting themselves in their relation to Christian doctrine, and the Christian community is readjusting itself likewise. The offensive features of Christian dogma, while still retained and advocated by some theologians and some communions, have been in great measure removed by other theologians and communions, and the process is going on with great rapidity. The war against science, criticism, literature, and art—all that is characteristic of our age—is gradually being limited to a smaller number of theologians and denominations, and there is ever an increasing number of theologians and churches which fully recognize all the achievements of modern times and who are at work in harmonizing them with the verified Christian dogmas in a larger, grander system—in a new theology representing all that is noblest and best in Christianity as applied to the modern world. While this process is going on, the dissatisfied ones will take some little time to find their new church homes and to adjust themselves to new conditions and circumstances.

So far as the great mass of mankind is concerned, the chief factor in the Christian religion is the fundamental one of the Christian life and the Christian institution, and the advance or decline of Christianity will be judged from this point of view. Here, however, we must recognize that there are several types of religious life which sometimes combine in one community, but which ordinarily exist apart as characteristic of different temperaments, different nations, different races. The lines of cleavage in historical Christianity are for the most part racial, national, or temperamental. We have to take this into account when we consider the religious life and institutions of different countries. What a difference there is in religion from this point of view in the great centers, such as Rome, St. Petersburg, Berlin, London, Edinburgh, New York! That man would go far astray who should undertake to use any one of these as a test of any or of all the others.

Let us consider, for example, the question of participation in the services of the Church. Rome has apparently, from a Protestant point of view, an abnormal number of churches, and in these churches an extraordinary number of chapels and altars. The reason for this is that there is an immense number of clergy in Rome, and all these altars are needed that they may perform the most important of their duties—the sacrifice of the mass. The churches, chapels, and altars are not erected for the people merely—if so, vastly fewer would be necessary—but for the priests who sacrifice for the people even when they are absent. Berlin has apparently very few churches, and these are not always well attended by the people, and are used infrequently except on Sundays. Judging from this, it would be a very irreligious city; but any one who really knows Berlin would not say that it is less religious than Rome. The religion of the German people finds its expression in a mystic type of personal piety and of family and social life; it maintains and propagates itself without frequent attendance upon public worship.

In London regular attendance upon public worship is commonly regarded as indispensable for the maintenance of the Christian religion. Therefore Christian people frequent the churches to an extent that is unknown on the continent of Europe. But to make the British habit of frequenting the Church for public worship a test of the vitality of the Christian religion in the great cities of the Continent would be altogether unjust and untrue. The historical development of religion in Great Britain has brought about an entirely different state of affairs there from that which we find everywhere else in the world. The situation in Great Britain is therefore special, peculiar, and, one might say, abnormal as compared with the situation in other parts of the world. In the United States the original population was chiefly British, and therefore followed British methods in religion. But in the present century our land, and especially our cities, have filled up with a population from the continent of Europe, bringing with them Continental methods of worship which would not yield to or readily adopt British methods. Intermarriage with the British stock and familiar converse in society have tended to assimilation, and therefore the situation has gradually and inevitably emerged that the Christianity of New York and Chicago and our other great cities has assumed an intermediate position between that of the Continent and that of Great Britain. The religious customs characteristic of British Christianity have undoubtedly declined—they have yielded to the influence of Continental Christianity. If British Christianity is the norm by which we are to judge, then Christianity has declined in the United States. If, however, it is not the norm, then it might appear that an intermediate position, such as we have attained by the assimilation of the British and the Continental types, may be a real advance and gain, because of the appropriation of some of the best features of both methods and the rubbing off of some of the eccentricities and excrescences of both. A decline in the relative attendance upon the public worship, and especially upon the second service on Sunday, is exactly what we would anticipate under the circumstances. It is altogether probable that the decline is much less than we had the right to expect in view of the vast influence exerted upon us by Continental types of Christianity during the past half century. And it is altogether probable that the decline has not reached its normal goal. Especially is this the case when we take into consideration other influences which tend to diminish the attendance upon public worship.

1. In Great Britain, where the churches were established by law, the state and Church were so entwined that it was a badge of good citizenship to attend upon public worship. In antithesis with this, attendance of the nonconformists upon public worship was regarded as a standing by their principles and a test of fidelity and courage. These influences worked also in the United States during the colonial period; but during the present century this motive has lost its influence, and it is to be feared that politicians as such feel under no special obligation to attend church, especially in view of the attitude of many of the ministry as to political life and political questions.

2. In Great Britain it has been a badge of social propriety to attend public worship. Social influences still prevail greatly in the United States, in villages and small cities, and even to some extent in the churches in the great cities, where they are organized and conducted in social lines as social religious clubs. But this influence is much weaker than it used to be, and it is gradually passing away.

3. The pulpit was once the chief means of instruction and of intellectual and moral stimulation for the people. The preacher was the people’s orator. The pulpit has in great measure lost its attractive power in this regard. The daily and weekly press have a greater influence in public instruction. The multiplication of cheap books also takes from the preacher a large share of his influence in this regard. Oratory in legislative bodies has to a great extent lost its influence. Its place has been taken by simple, compact, time-saving statements, often printed but not delivered. Committees do the work which used to be done after discussion before the public. So the people will not listen now to the pulpit orator of former generations. They demand short, crisp sermons that bristle with points, and are practical and helpful. In other words, the oratorical and highly intellectual character of the pulpit which used to attract worshipers no longer attracts them. They feel that they can get more benefit in this regard by reading in the comfort of the home. Multitudes of people can no longer be induced to attend church to be instructed by the minister or to get his judgment on topics of the time, or to be stirred by his eloquence; they can get all these things cheaper and easier by reading at home. When, now, this is re-enforced by the fact that multitudes dislike the doctrines of the Church, and resent them when they are preached, we can easily understand that church attendance should decline very greatly from this reason.

But this is no evidence that the Christian religion has declined. If men absent themselves from public worship because it is no longer necessary for them, as good citizens and as respectable members of society, to attend, or because they may get their instruction and stimulation elsewhere easier and with less expenditure of time and money, that is simply an evidence that attendance upon church in the past has been due in great measure to other than religious reasons, and that, these no longer holding, attendance has disappeared with them. The attendance upon public worship, though reduced so far as number is concerned, is now more simply and purely for religious reasons, and therefore minister and people may with greater freedom make the services more distinctly religious.

This is indeed the real situation that has emerged. The sermon has declined relatively in importance, and rightly so. It had an exaggerated importance in the Protestant Church, especially in the non-liturgical churches. There is a world-wide tendency now, which is increasing in power, to improve and enlarge the worship of the Church. Liturgies and ceremonies of worship are more discussed now in the Protestant world than are sermons and lectures, because it is becoming every day more evident that the Church is organized for common prayer and for public worship, and not merely to furnish a pulpit for a minister. The pulpit is more and more being merged in the worship, and is losing its domination over the worship. With this tendency goes increased attention to the Holy Sacraments, especially the Holy Communion, more frequent celebrations and more frequent participation, increased opportunity of worship during Sunday and during the week, and also therewith the greatly increased attention to the organization of the Church for aggressive Christian work. Those who think that the pulpit is everything in the public service naturally suppose that with the decline of the pulpit Christianity declines, but those who think that public worship is the essential thing in the Church rejoice at the changes that are taking place, and hold that Christianity is advancing. They maintain that it is not so important for the Church to gather large crowds to listen to the sermon as it is for the church doors to be ever open, with frequent services for the convenience and help of worshipers at any time, without regard to whether they are few or many, assured that thereby a much greater number of people are reached and benefited than by the former limited methods.

It is sometimes said that biblical criticism has undermined faith in Holy Scripture, and that, therefore, many absent themselves from public worship. But there is no real evidence for it. I doubt not that the opponents of biblical criticism drive many people from their congregations, just as they do when they attack the sure results of modern science, or expose their ignorance in the discussion of political and economical questions in which they have not been trained; but these people simply remove to other congregations where they will not be offended by obscurantism and intolerance. Biblical criticism really makes the Bible more attractive to the people, and its reading and exposition more interesting and influential in the Church.

A careful study of the situation makes it evident that the Christian religion is not declining in our land; but it is passing through a transition state, putting off antiquated dogmas, customs, and methods, and adapting itself to the modern world, and transferring itself so as to better accomplish its work. In no age has Christianity made more advance than in the century now drawing to a close.

The Indians of Bolivia are described by Sir Martin Conway as “an exceedingly bigoted folk, retaining under a mask of Christianity their ancient superstitions, little altered,” and are kept in order by priestly management rather than by force. Mr. Conway was seriously interfered with by them in the prosecution of his researches because the nature of his undertaking involved some outrage to their superstitions. They regard the mountains above the level of habitation as part of the other world, and holding, among other fancies, that a golden bull and a golden cross planted by supernatural agency stood on the summit of one of the peaks round the base of Mount Serata, thought that the object of the explorer’s expedition could be nothing else than to obtain possession of these priceless treasures. Hence they offered formidable opposition to him.

A CENTURY OF GEOLOGY.A
By Prof. JOSEPH LE CONTE.

Geology is one of the youngest of the sciences. It may almost be said to have been born of the present century. It is true that knowledge concerning the structure of the earth had been accumulating ever since the time of the Greeks and Romans; it is true that these materials became more abundant and were better organized in the eighteenth century; but this knowledge had not yet taken form as a distinct branch of science until about the end of that century. There are two distinctive marks of scientific as compared with popular knowledge: First, that its fundamental idea is clearly conceived; and, second, that its method is distinctly inductive.

1. Fundamental Idea.—The fundamental idea underlying geological thought is the history of the earth. Now, until the beginning of the present century the earth was not supposed to have any history. It was supposed to have been made at once, out of hand, about six thousand years ago, and to have remained substantially unchanged ever since as the necessary theater of human history. Changes were known to have taken place and in less degree to be still taking place, but these were not supposed to follow any law such as is necessary to constitute a history, and thus to constitute a science distinct from geography. Buffon, about the middle of the last century, did indeed bring out dimly the idea of an abyss of time, preceding the advent of man, in which the earth was inhabited by animals and plants wholly different from those of the present day, but he was compelled by the priests of the Sorbonne to retract these supposed irreligious views. So tardily was the fundamental idea of geology clearly conceived that Comte, the great originator of scientific philosophy, in his classification of the sciences in 1820, denied a place to geology because, according to him, it was not a distinct science at all, but only a field for the application of all the sciences. It is evident that he did not perceive the fundamental idea underlying geology and distinguishing it from geography—viz., a life history of the earth through all time. The claim of geology to a place in a scheme of classification is exactly the same as that of astronomy. As astronomy is a field for the application of mathematics, mechanics, physics, and, recently, chemistry, but is distinguished from them all by its characteristic fundamental idea of illimitable space, so geology is a field for the application of all other lower sciences, but is distinguished from them all by her characteristic fundamental idea of illimitable time. As all other sciences are terrestrial, but astronomy alone celestial, so all other sciences belong to the present—the “now”—but geology alone belongs to the illimitable past. The fundamental idea of the one is infinite space, of the other infinite, in sense of inconceivable, time. All other sciences, including astronomy, are but a flash-light view of Nature. Geology alone is a view of Nature in continuous movement, a life history—an evolution of Nature. This mode of thought began to dawn only in the closing years of the last and the opening years of the present century. It seems to have been first clearly conceived by the mind of Hutton in the last part of the eighteenth century.

2. Inductive Method Applied.—When the true idea underlying geology was clearly conceived and geology thus distinctly separated from other departments of science, geology may be said to have been born. But it was still in helpless infancy, its growth irregular, and even its continuous life uncertain, because a solid basis of inductive method was not yet laid. That basis was laid mainly by Hutton in 1795,B and still more clearly by Charles Lyell in 1830, in the principle that the study of causes now in operation is the only true foundation of geology.

Geological changes, of course, belong to the irrevocable past, and are therefore hopelessly removed from direct observation. Their causes and process must be reconstructed by the skillful use of the scientific imagination. Until Lyell, more or less probable hypotheses seemed all that was possible. What a field was here for the conflict of opposite extreme views! But Lyell showed that “causes now in operation” are producing similar effects under our eyes, if we will only observe. From that moment geology became a truly inductive science and its indefinite progress assured.

These two events, then—viz., the conception of geology as a distinct science, and the introduction of a true scientific method—are the greatest epochs in the history of geological science. Some dim adumbrations of these appear before this century, especially the former in the mind of Buffon, and the latter somewhat fully in the mind of Hutton, but they were not generally accepted and had not become working principles until the beginning and even some time after the beginning of the nineteenth century. These must be borne in mind in all we have further to say of the progress of geology through the century.

When the century opened, the war between the Neptunists and the Plutonists, between the Wernerites and the Huttonites, was still going on, but was approaching the usual result in such cases of dispute—viz., the recognition of the fact that there was truth on both sides, and they must be combined into a more comprehensive view. The chief difference of opinion still remaining was as to the relative importance of the two agencies, aqueous and igneous. Two great advances took place about the beginning of this century: William Smith, by patient, painstaking field observation and mapping, laid the foundation of stratigraphy; and Cuvier, by his profound and brilliant studies of the wonderful discoveries of extinct mammals in the Eocene basin of Paris, laid the foundations of paleontology. These researches placed in clearer light than ever before the existence of other time-worlds before the present one. William Smith published his tabular view of the British Strata in 1790, but his map was not completed and published until 1815. Cuvier’s great work on the Organic Remains of the Paris Basin was published in 1808.

Thus, early in the century the two bases of our science were laid by Smith and Cuvier. We now proceed to touch lightly only the main steps of subsequent growth through the century.

As, in the previous century and the early part of this, the discussion was between the opposite schools of Neptunists and Plutonists, with the final result of reconciliation in a more scientific view which combined these two surface views into a stereoscopic reality, so now the discussions began between catastrophism and uniformitarianism, and ended with a similar final result. Geologists, in the early part of the century, before the study of causes and processes now in operation was generally acknowledged as the only rational basis of a true scientific geology, seeing the frequent unconformities in the geological series and the apparently sudden changes of life forms associated with these unconformities, were naturally led to the conclusion that the whole history of the earth consisted of a series of sudden and violent catastrophes by which the bed of the ocean was suddenly raised and its waters precipitated on the land as a great wave of translation, carrying universal ruin and extermination of all life in its course. Such catastrophes were supposed to be followed by periods of quiet, during which the new earth was repeopled, by direct act of creation, with new forms of life adapted to the new conditions.

This view was in perfect accord with the then accepted doctrine of the supernatural origin and the permanence of species. Species were supposed to have been created at once, out of hand, without natural process, in some place (center of specific origin), spread in all directions as far as physical conditions would allow, but remained unchanged and unchangeable as long as they continued to live or until another universal exterminating catastrophe. Species are “medals of creation.” They are successive individuals struck from the same die, until the die is worn out or broken. Then a new die is made, and the process of coinage of identical individuals is renewed.

Thus the whole history of the earth was supposed to consist of a succession of alternate supernatural and natural events. The catastrophes were supernatural; the times of quiet were natural. The creation of new dies or creation of first individuals was supernatural; the coinage of individuals of successive generations was natural. But on the whole the successive conditions of physical geography and the successive faunas and floras were higher and more complex according to a preordained plan. The great apostles of catastrophism were Cuvier in France and Buckland in England. According to Buckland, the last of these great catastrophes was the Quaternary or drift period, and this period was, by him and by many others since, associated with the Noachian Deluge.

Lyell opposed this view with all his power. According to him we can not judge of geological causes and processes except by study of causes and processes now in operation and producing effects under our eyes. The slow operation of similar causes and processes is sufficient—given time enough—to account for all the phenomena in geological history. Thus arose the extreme opposite doctrine of uniformitarianism. Things have gone on from the beginning and throughout all time much as they are going on now. This view, of course, required illimitable time, and was of great service in enforcing this idea. But, in revulsion from the previous idea of catastrophism, it undoubtedly was pushed much too far.

Meanwhile the theory of evolution was incubating in the mind of Darwin. Even Lyell, while he established the doctrine of slow uniform changes so far as inorganic Nature was concerned, was still compelled to admit supernatural catastrophic changes in organic Nature. Species, even for Lyell, were still immutable—still there were supernatural creation of first individuals, and continuance of similar individuals by natural process of generation. On the publication of Darwin’s Origin of Species by Descent with Modification, Lyell at once embraced the new view as a completion of his principle of causes now in operation and his doctrine of uniformitarianism. In a certain superficial sense evolution is certainly confirmatory of the doctrine of uniformity of causes and processes in the past and the present, but in a deeper sense it is quite contrary in its spirit. Uniformitarians of the Lyell school look upon geology as a chronicle of events—evolutionists as a life history of the earth. The one regards the slow changes as irregular, uncertain, without progress or purpose or goal; the other as an evolution to higher and higher conditions, as a gradual movement onward toward the present condition and toward man as its goal. The recognition of this is only now approaching clearness. If geology is the history of the evolution of the earth from primal chaos until now, then the conditions have changed at every step, and absolute uniformity is impossible. Extreme uniformitarianism is therefore untenable. Catastrophism and uniformitarianism are opposite extremes which must be combined and reconciled. This reconciliation is only now being completed, and we therefore put off its discussion for the present. Suffice it to say now that geologic thought in this regard has passed through three stages—catastrophism, uniformitarianism, and evolutionism. And this latter is the final stage, because (1) it is a complete reconciliation between the other two, and (2) because it is plastic and indefinitely modifiable and progressive, while the other two are equally rigid and unchangeable by their mutual antagonism.

With these fundamental principles in mind, we proceed to touch briefly the most important advances during the century.

EVOLUTION OF EARTH FORMS.

The idea of the progressive development of the earth in its greater features throughout all geologic time by the action of forces resident in the earth itself preceded the acceptance of the evolution of organic forms. We have said that the fundamental idea of geology is that of the evolution of the earth through all time. Now, it was Dana who first studied geology wholly from this point of view. For him geology was the development of the earth as a unit. Before him, doubtless, geology was a kind of history—i. e., a chronicle of thrilling events—but Dana first made it a philosophic history. Before Dana, geology was an account of the succession of formations and their fossil contents. Dana made it an account of the evolution of earth forms and the concomitant and resulting evolution of organic forms. It is true that first and for a long time his evolutional conception was incomplete. It is true that while he attributed the evolution of earth forms to natural causes and processes, he still shrank from applying similar causes to the changes in life forms, but this was the almost necessary result of the then universal belief in the supernatural origin and the unchangeableness of organic forms. He lived to make his conception of evolution as a natural process, both of the earth and of organic forms, complete.

Ocean Basins and Continents.—If we divide geological causes and processes into two general kinds as to their origin—viz., internal, or earth-derived, and external, or sun-derived—evidently the former is the original and fundamental kind. These determine earth forms, while the other only modify them; these determine the great features, the other only the lesser features; the former rough-hews the earth features, the latter shapes them. It is the effects of these interior earth forces which are the most important to study. And among these effects the most fundamentally important of all is the formation of those greatest features—the ocean basins and continental arches. The most probable view is that they are formed by unequal radial contraction in the secular cooling of the earth. The earth was certainly at one time an incandescently hot mass, which gradually cooled and contracted to its present temperature and size. Now, if it were perfectly homogeneous both in density and in conductivity in all parts, then, cooling and contracting equally in every part, it would retain its symmetric oblate-spheroid form, though diminishing in size. But if there were any, the least, heterogeneity either in density or especially in conductivity over large areas, then the more conductive areas, contracting more rapidly toward the center radially, would form hollows or basins, and the less conductive areas would stand out as higher arches. Thus were formed the oceanic basin and the continental arches of the lithosphere. The same causes which produced would continue to increase them, and thus the ocean basins would increase in depth and the continents in height.

The hydrosphere is still to be added. In the beginning of this process doubtless the lithosphere was hot enough to maintain all the water in the form of vapor in the atmosphere. But when the surface was cool enough the water would precipitate and partly or wholly cover the earth—whether partly or wholly would depend on the amount of precipitated water and the amount of inequality which had already taken place. The amount of water, as we know, is sufficient, if the inequalities were removed, to cover the whole surface two and a half miles deep. Inasmuch as the forming of the inequalities is progressive and still going on, it seems improbable that the inequalities had become sufficiently great, at the time of precipitation, to hold the waters. If this be so, then the primeval ocean was universal and the future continents existed only as continental banks in the universal ocean.

However this may have been, there seems little doubt that the same cause which produced the inequalities continued to operate to increase them. The ocean basins, so far as these causes are concerned, must have become deeper and deeper, and the continents larger and larger. In spite of many oscillations producing changes mostly on the margins, but sometimes extending over wide areas in the interior of the continent, this, on the whole, seems to be in accordance with the known geological history of the earth. If so, then the oceanic basins have always been oceanic basins, and the places of the continents have always been substantially the same. This introduces a subject on which there has been much discussion recently—viz.:

The Permanency of Ocean Basins.—Closely associated with the Lyellian uniformitarianism was the doctrine of extreme instability of earth features, especially the forms and places of sea and land. Crust movements were irregularly oscillating to such a degree that in the course of geologic history sea and land frequently and completely changed places. Abundant evidence of this was supposed to be found in the unconformities so frequent in the stratified series. The tendency of that time was toward a belief in up-and-down movements, back-and-forth changes, without discoverable law, rather than progressive onward movement. On first thought it might seem that such lawless movement was rather in keeping with catastrophism than uniformitarianism. But not so, for the movements are supposed to be very slow. Again, it might seem on first thought that gradual progressive change—in a word, evolution—would be peculiarly in accord with uniformitarian ideas. But again not so, because this doctrine was, above all, a revulsion from the idea of supernatural purpose or design or goal contained in catastrophism. Uniformitarianism strongly inclined toward purposelessness, because of its supposed identity with naturalism. Thus for a long time, and still with many geologists, the tendency is toward a belief in irregular movements without discoverable law, toward instability of even the greatest features of the earth—viz., sea basins and continental arches. Geology for them is a chronicle, not a life history.

The contrary movement of thought may be said to have commenced with Dana. Dana studied the earth as a unit, as in some sense an organism developing by forces within itself. The history of the earth is a life history moving progressively toward its completion. The forces originating oceanic basins and continental arches still continue to deepen the former and enlarge the latter. From this point of view, oceanic basins and continental arches must have always been substantially in the same places. Oscillations there have been at all times and in all places, but they affect mainly the outlines of these great features, though sometimes affecting also the interior of continents and mid-sea bottoms, but not sufficiently to change greatly their general form, much less to interchange their places.

Such is the doctrine of permanency of oceanic basins. It is undoubtedly a true doctrine, but must not be held in the rigid form characteristic of early thought. The forces originating oceanic basins still continue to deepen them and to increase the size and height of continents, but other forces are at work, some antagonizing (i. e., cutting down the continents and filling up the ocean beds), and still others determined by causes we little understand, by oscillations over wide areas, greatly modifying and often obscuring the effects of the basin-making movements. Here, then, we have two kinds of crust movements: the one fundamental and original, determining the greatest features of the earth and moving steadily onward in the same direction, ever increasing the features which it originates; the other apparently lawless, uncertain, oscillating over very wide areas, modifying and often obscuring the effects of the former. The old uniformitarians saw only the effects of the latter, because these are most conspicuous; the new evolutionists add also the former and show its more fundamental character, and thus introduce law and order into the previous chaos. The former is the one movement which runs ever in the same direction through all geologic time. The latter are the most common and conspicuous now and in all previous geologic time. The former underlies and conditions and unifies the history; the latter has practically determined all the details of the drama enacted here on the surface of the earth. Of the causes of the former we know something, though yet imperfectly. Of the causes of the latter we yet know absolutely nothing. We have not even begun to speculate profitably on the subject, and hence the apparent lawlessness of the phenomena. A fruitful theory of these must be left to the coming century.

Mountain Ranges.—If oceanic basins and continental domes constitute the greatest features of the earth’s face, and are determined by the most fundamental movements of the crust, surely next in importance come great mountain ranges. These are the glory of our earth, the culminating points of scenic beauty and grandeur. But they are so only because they are also the culminating points, the theaters of greatest activity, of all geological forces, both igneous and aqueous—igneous in their formation, and aqueous both in the preparatory sedimentation and in the final erosive sculpturing into forms of beauty. A theory of mountain ranges therefore lies at the bases of all theoretical geology. To the pre-geologic mind mountains are the type of permanence and stability. We still speak metaphorically of the everlasting hills. But the first lesson taught by geology is that nothing is permanent; everything is subject to continuous change by a process of evolution. Mountains are no exception. We know them in embryo in the womb of the ocean. We know the date of their birth; we trace their growth, their maturity, their decay, their death; we even find in the folded structure of the rock, as it were, the fossil bones of extinct mountains. In a word, we are able now to trace the whole life history of mountains.

Mountains, therefore, have always been a subject of deepest interest both to the popular and the scientific mind—an interest intensified by the splendors of mountain scenery and the perils of mountain exploration. The study of mountains is therefore coeval with the study of geology. As early as the beginning of the present century Constant Prevost observed that most characteristic structure of mountains—viz., their folded strata—and inferred their formation by lateral pressure. All subsequent writers have assumed lateral pressure as somehow concerned in the formation of mountains. But that the whole height of mountains is due wholly to this cause was not generally admitted or even imagined until recently. It was universally supposed that mountains were lifted by volcanic forces from beneath, that the lifted strata broke along the top of the arch, and melted matter was forced through between the parted strata, pushing them back and folding them on each side. And hence the typical form of mountain ranges is that of a granite axis along the crest and folded strata on each flank. But attention has lately been drawn to the fact that some mountains, as, for example, the Appalachian, the Uintah, etc., consist of folded strata alone, without any granite axis. In such ranges it is plain that the whole height is due not to any force acting from below, but to a lateral pressure crushing and folding the strata, and a corresponding thickening and bulging of the same along the line of crushing. Then the idea was applied to all mountain ranges. So soon as the prodigious amount of erosion suffered by mountains, greater often than all that is left of them, was fully appreciated, it became evident that the granite axis so characteristic of mountains was not necessarily pushed up from beneath and protruded through the parted strata, but was in many cases only a sub-mountain core of igneous matter slowly cooled into granite and exposed by subsequent erosion greatest along the crest.

Next, attention was drawn to the enormous thickness of the strata involved in the folded structure of mountains. From this it became evident that the places of mountains before they were formed were marginal sea bottoms off the coasts of continents, and receiving the whole washings of the continents. Thus the steps of the process of mountain formation were (1) accumulation of sediments on offshore sea bottoms until by pari passu subsidence an enormous thickness was attained. This is the preparation. (2) A yielding along these lines to the increasing lateral pressure with folding and bulging of the strata along the line of yielding, until the mountain emerges above the ocean and is added to the land as a coast range. This is mountain birth. (3) As soon as it appears above the water it is attacked by erosive agents. At first the rising by continuance of the crushing and bulging is in excess of the erosion, and the mountain grows. This is mountain youth. (4) Then supply and waste balance one another, and we have mountain maturity. (5) Then the erosive waste exceeds the growth by up-bulging, and mountain decay begins. (6) Finally, the erosive forces triumph and the mountain is clean swept away, leaving only the complexly folded rocks of enormous thickness to mark the place of a former mountain. This is mountain death. Such briefly is the life history of a mountain range.

In all this we have said nothing about causes. In this connection there are two points of especial importance: (1) Why does the yielding to lateral pressure take place along lines of thick sediments? (2) What is the cause of the lateral pressure?

1. Cause of Yielding to Lateral Pressure along Lines of Thick Sediments.—The earth was once very hot. It is still very hot within, and still very slowly cooling. If sediments accumulate upon a sea bottom the interior heat will tend to rise so as to keep at the same distance from the surface. If the sediments are very thick, say five to ten miles, their lower parts will be invaded by a temperature of not less than 500° to 1,000° F. This temperature, in the presence of water (the included water of the sediments), would be sufficient to produce softening or even fusion of the sediments and of the sea floor on which they rest. This would establish a line of weakness, and therefore a line of yielding, crushing, folding, bulging, and thus a mountain range. In the first formation of a range, therefore, there would necessarily be a sub-mountain mass of fused or semifused matter which by the lateral crushing might be squeezed into cracks or fissures, forming dikes. But in any case the sub-mountain mass would cool into a granite core which by erosion may be exposed along the crest. The explanation seems to be satisfactory.

2. Cause of the Lateral Pressure.—No question in geology has been more discussed than this, and yet none is more difficult and the solution of which is more uncertain. But the most obvious and as yet the most probable view is that it is the result of the secular contraction of the earth which has gone on throughout its whole history, and is still going on.

It is admitted by all that in an earth cooling from primal incandescence there must come a time when the surface, having become substantially cool and receiving heat also from the sun, would no longer cool or contract, but, the interior being still incandescently hot, would continue to cool and contract. The interior, therefore, cooling and contracting faster than the exterior crust, the latter following down the ever-shrinking nucleus, would be thrust upon itself by a lateral or tangential pressure which would be simply irresistible. If the earth crust were a hundred times more rigid than it is, it still must yield to the enormous pressure. It does yield along its weakest lines with crushing, folding, bulging, and the formation of mountain ranges.

This is the barest outline of the so-called “contractional theory of mountain formation.” Very many objections have been brought against it, some of them answerable and completely answered, but the complete answer to others must be left to the next century. Perhaps the greatest objection of all is the apparent insufficiency of the cause to produce the enormous amount of folding found not only in existing mountains but in the folded structure of rocks where mountains no longer exist. But it will be observed that I have thus far spoken only of contraction by loss of heat. Now, not only has this cause been greatly underestimated by objectors, but, as shown by Davison and especially by Van Hise, there are many other and even greater causes of contraction. It would be out of place to follow the discussion here. The subject is very complex, and not yet completely settled.

We have given the barest outline of the history of mountain ranges and of the theory of their formation as worked out in the last third of the present century, and, I might add, chiefly by American geologists. So true is this, that by some it has been called the “American theory.”

Oscillatory Movements of the Earth’s Crust over Wide Areas.—We have already spoken of these as modifying the effect of the ocean-basin-making movements, and therefore now touch them very lightly. These differ from the movements producing oceanic basins on the one hand and mountain ranges on the other, by the fact that they are not continuously progressive in one direction, but oscillatory—now up, now down, in the same place. Again, they do not involve contraction of the whole earth, but probably are always more or less local and compensatory—i. e., rising in one place is compensated by down-sinking in some other place. Nevertheless, they often affect very wide areas—sometimes, indeed, of more than continental extent—as, for example, in the crust movements of the Quaternary period or ice age.

These are by far the most frequent and most conspicuous of all crust movements—not only now, but also in all geological times. If ocean-basin-forming movements are the underlying cause and condition of the evolution of the earth, these wide oscillations, by increasing and decreasing the size and height of continents and changing greatly their contours, have determined all the details of the drama enacted on the surface, and were the determining cause of the varying rates and directions of the evolution of the organic kingdom. These were the cause of the unconformities and the corresponding apparent wholesale changes in species so common in the rocky strata, and which gave rise to the doctrine of catastrophism of the early geologists. These also have so greatly modified the contours of the continents and their size by temporary increase or decrease that they have obscured the general law of the steady development of these, and therefore their substantial permanency.

Although the most important of all crust movements in determining the whole history of the earth, and especially of the organic kingdom, we shall dwell no further on them, because no progress has yet been made in their explanation. This, too, must be left to the workers of the twentieth century.

The Principle of Isostasy.—The principle of static equilibrium as applied to earth forms was first brought forward (as so many other valuable suggestions and anticipations in many departments of science) by the wonderfully fertile mind of Sir John Herschel, and used by him in the explanation of the sinking of river deltas under the increasing weight of accumulating sediments.C It was afterward applied to continental masses by Archbishop PrattD and by the Royal Astronomer Professor Airy.E But for its wide application as a principle in geology, its clear definition, and its embodiment in an appropriate name, we are indebted to Major Dutton, United States Army.F