The laboratories consist of a series of rooms facing northward and westward, with special facilities for taxonomic, embryological and morphological investigations. Physiological and photographic darkrooms, the experiment room for living plants and chemical laboratories offer especially ample opportunities for the record and development of practically all phases of plant physiology. The laboratories, library and herbarium are open to the graduate students from Columbia University, in addition to those from other institutions of learning who may register directly at the Garden. The latter, in return, have the privileges of students at Columbia University.

A weekly convention of all of the workers in botany in New York City is held in the museum, at which the results of recent researches are given or an address is made by an invited speaker from out of the city.

The area of the Garden presents a very irregular topography, comprising, as it does, a half mile of the valley of the Bronx River, low marshes and swamps, artificial lakes, open glades, with heavy peaty soil, upland plains with gravelly sandy soil, granite ridges, and about seventy acres of natural forest. About forty acres of this forest consist of a dense grove of hemlocks, which has never been seriously disturbed by the hand of man. It is truly remarkable that the City of New York should include within its boundaries a primitive forest of this size, and this invaluable feature is to be preserved forever by a special contract between the Garden and the Department of Public Parks. Since a hemlock forest is a climactic formation, and is not replaced by any other growth unless cut down, it may be expected to endure through the present geological epoch, barring the accidents of flood, storm and fire. The great diversity of conditions offered by the natural features of the Garden gives it a very rich population of indigenous plants. A census of the ferns and seed-plants at the time the tract was converted to its present purpose showed nearly a thousand species.

The entire area has been handled most sympathetically by those in charge of the architectural features of the Garden. The buildings were erected in the more open western part of the grounds, which offered the least valuable landscape features, and the surface around them has been improved by plantings. The natural beauties of the tract have been most zealously guarded from disturbances of all kinds. The attractive panoramas of wild woodland and stream offered to the artist and lover of nature have been left absolutely untouched, but made more valuable by increased ease and safety of access.

A number of special biological groups of plants have been established in suitable places in various parts of the Garden. The trees are in the arboretum east of the Bronx on the side and summit of a long ridge; unassorted and reserve material of all kinds is kept in the nurseries on the eastern slope of the same ridge; the salicetum is established on the border of the marsh in the northern end of the Garden, giving the willows and poplars the conditions under which they grow best. The fruticetum occupies an adjoining upland plain underlaid with gravel to a depth of twenty feet, affording space for the cultivation of a large number of shrubs, while the conifers are located on slopes to the westward of the hemlock forest. The viticetum is along the western edge of the forest, and the trellises of logs and timbers, extending for a length of six hundred feet, give suitable support to the vines. The herbaceous plantation occupies an open glade to the westward of the forest, and lies between two granite ridges. It is traversed through the middle by a small stream widened at places into lagoons for aquatic forms. About twenty-two hundred species are now in cultivation in this plantation. The wide border plantations which are established along the boundaries also offer opportunities for the growth of a great variety of trees, herbs and shrubs.

The horticultural houses, also erected by the City for the Garden, are located in the western part of the grounds at some distance to the south of, and facing, the museum. A palm-house, with a total height of dome of ninety feet, is the central feature, from which lower ranges extend on either side, making a total length of front of five hundred and twelve feet. The horticultural houses, as well as the museum, are heated by steam furnished by a power house beside the railroad on the extreme edge of the Garden.

The collections of living plants in the plantations are arranged in the same system as the synoptic collection in the museum. Every plantation contains species of similar habit, and the horticultural houses are used for the cultivation of forms which may not endure the outdoor climate of this locality. Not only are the plants from warmer zones grown under glass, but when it is desired to develop native species out of their season, they may be forced and brought to full development and bloom in the winter.

The construction of driveways and paths is being prosecuted by the Park Department with all available funds at their commands.

Public appreciation of the natural beauties of the Garden, and of the phases of botany illustrated by its collections has been most gratifying, as shown by the great and constantly increasing number of visitors. The series of popular lectures given in the museum on Saturday afternoons have been well attended. The Journal of the Garden, which serves as a means of communication with its members, brings to the notice of its readers interesting facts in botany, horticulture and forestry, and records a constantly swelling list of gifts of books, specimens and plants.

The library, herbarium and laboratories have been open for only a few months, yet twenty-two students have taken advantage of the facilities thus afforded during the collegiate year now closing. Investigations of importance have been carried forward by these students, by members of the staff, and by the members of the staff of Columbia University. The results of some of these investigations have been published in the Bulletin of the Garden, which also contains the official reports of the organization. Papers written by members of the staff or students are reprinted from the periodicals in which they appear as contributions, while a fourth series of Memoirs has been found necessary for the presentation of papers of great length.

Not the least important of the investigating functions of a garden consists in its participation in the exploration of remote or unknown parts of the world in an effort to obtain a better knowledge of the plant population of the earth. During the brief period of its activity the Garden has already carried out work of this character in the Rocky Mountains and in Porto Rico.

The ordinary work of the Garden is maintained by the income from its endowment fund, by the annual dues of its members (now numbering over eight hundred) and by an annual appropriation by the City. Its board of managers is authorized to hold and administer trust funds, and it is hoped by the aid of gifts or bequests for special or general purposes to expand its usefulness in directing investigation. Already it has been favored by a bequest of a considerable sum of money by the late ex-Chief Justice Charles P. Daly, which may be devoted to any purpose determined by the board of managers.

GAS AND GAS METERS.
By HUBERT S. WYNKOOP, M. E.

What is the matter with our illuminating gas? Why is its quality so poor? Why is it that our bills are creeping up, in spite of the fact that the rate per thousand cubic feet is going down? These are questions that periodically recur to the mind of every householder.

Just why the public has not been educated into a correct understanding of the gas situation is hard to say, unless it be that an inbred prejudice against believing the word of any corporation has led to an utter repudiation of such explanatory statements as may emanate from time to time from the gas office. And it must be admitted that many of the explanations are misleading, either through the intention of the superior officials or by reason of the ignorance of their subordinates.

Hardly has the chill of shortening days driven us indoors in the early twilight before complaints of poor gas become epidemic. Now, what is ‘poor’ gas? Is the gas deficient in light-giving constituents, or is it merely burned in such a manner as not to afford a satisfactory illumination?

The charter of Greater New York requires that the illuminating gas supplied throughout the city shall be of at least twenty candle power, or illuminating quality, or richness—that is to say, if we burn this gas in a standard burner at the standard pressure (or at as near this pressure as may be), so that the rate of consumption is five cubic feet an hour, the flame thus produced shall be equivalent to twenty standard sperm candles, each burning at the rate of one hundred and twenty grains of sperm per hour, and all bunched—if such a thing were possible. There can be hardly any doubt but that all the gas sent out from modern gas works fulfills the above requirement. Indeed, my own tests give results ranging from twenty-two to twenty-eight candles, with an average of about twenty-four. Manifestly, the gas sent out is not ‘poor.’

Nevertheless, the fact that the gas as manufactured is of the required candle power is no indication that the product as delivered to the consumer will give a similarly satisfactory test. Distribution of gas is attended with many perplexities, not the least of which is condensation. The illuminating hydrocarbons, or light-giving constituents held in suspension in the gas, are not so firmly fixed therein as to be unaffected by the size of the pipe, the character of the internal pipe surface, and barometric and thermometric variations. The transmission of gas causes, therefore, a loss of candle power ranging from a small fraction to several candles, although it is possible to conceive of conditions so extraordinarily favorable that the illuminating quality of the gas might be actually improved by distribution.

It will be readily understood from this explanation that tests made at the gas works, or even at points arbitrarily selected at a certain distance from these works, are hardly calculated to satisfy the consumer. For this reason I have preferred, in conducting these tests, to sacrifice to some degree the accuracy that obtains in laboratory experiments, in order to test gas samples taken from the main directly in front of the complainant’s own premises. I argue that the consumer cares little or nothing as to whether the gas as manufactured complies with the law, or whether tests made at a point perhaps a mile away from the works show the required candle power; but that he does want to know what is the quality of the gas passing in at his service pipe. The method of collecting and transporting to a laboratory the gas samples enables one to say with positiveness that the gas at the point of complaint has an illuminating power of at least so many candles, and that it may be even one candle better than the tests indicate. The figures thus obtained range from twenty and a half to twenty-five. So, then, the gas delivered to the consumer is not ‘poor.’

Hygienic reasons demand that the impurities in the gas shall not exceed a definite percentage. Whatever effect these impurities may have upon the candle power has been covered by the tests above explained, so that any further consideration of these impurities may be omitted here.

It is always a difficult matter to convince an indignant householder that the quality of the gas supplied to him is satisfactory. He knows perfectly well that he is not getting the desired result, and no explanation, however elaborate, as to candle power will placate him, unless it be supplemented by a further statement detailing the cause of the trouble. When you are trying to draw water in the bathroom while the cook is filling the washtubs in the basement, do you say the water is ‘poor’? Why, then, should you characterize the gas as ‘poor,’ when people nearer to the gas works than you are happen to be drawing heavily upon the common gas main? Imagine, if you please, a long gas main, with consumers tapping in at points throughout its entire length, and with a gas holder forcing the gas in at one end. Since there is a loss of pressure, caused by the transmission, it follows that the pressure will be higher at the gas holder than anywhere else along the line, the difference in pressure depending, roughly, upon the size and length of the pipe and upon the amount of gas flowing. Now, for any one customer the size and length of pipe will remain constant, but the flow of gas along the line will vary from hour to hour, consequently the pressure at his house may be expected to vary from hour to hour.

The unit of measurement of gas pressure is that pressure which will cause a difference of water level of one tenth of an inch in the two legs of a V-shaped tube when one end is connected with the gas main and the other end is left open to the outer air. Ten tenths, or one inch, is the standard, or normal pressure.

Any appliance—even a gas-burner—operates to best advantage under certain well-defined conditions. Depart from these conditions, and the efficiency of the device is impaired to an extent depending largely upon the nature of the appliance under consideration. For example, burn an incandescent lamp at fifty per cent. above normal voltage and it breaks down; burn a gas jet at two hundred per cent. above normal pressure, and it still operates—how satisfactorily ‘deponent sayeth not.’ Now, the gas-burner is supposed to operate to best advantage at ten tenths of an inch. At this pressure the flame is neither so wavering as to be affected by every chance draught, nor so rigid as to permit the gas to blow through without being properly consumed. Below the normal the flame decreases; above, the light is increased somewhat, but not by any means in proportion to the increase in the gas flow. Thus we see that the satisfactory employment of gas as an illuminant depends upon the maintenance of a pressure high enough to deliver the required amount of gas, but not so high as to cause wasteful consumption.

Turning back now to the gas main, let us consider the pressures actually existing. Exhibit 1 is a photograph of a twenty-four-hour record of pressure at a point not far from the works. The radial lines represent time, and there is a line for each quarter of an hour. The circles represent pressure, there being one circle for each tenth of an inch. Starting at E, the point at which the record begins, and following the irregular line clockwise, one may readily determine the fluctuations of pressure and the time of their occurrence. Interpreting the diagram, we find that the pressure was slightly above the normal until 4.30 P. M. (A), when the works began to raise the pressure little by little, in order to compensate for the increased loss due to increased flow through the mains. At 6.15 P. M. (B), the works ceased increasing the pressure. While this increase lasted—from 6.15 P. M. (B) to 10.15 P. M. (C)—our friend near the works suffered under twenty-one tenths pressure, the gas blowing merrily through the tips and the meter conscientiously registering gas wasted as well as gas utilized. From 10.15 P. M. (C) the pressure falls by steps during the ensuing two hours, finally reaching eleven tenths just after midnight (D), which latter pressure is quite steadily maintained until the following forenoon. The service from bedtime to dinner time should have proved quite satisfactory. One would naturally expect to find this consumer complaining of high bills, however.

Visiting the fellow at the distant end of the line, we find conditions widely at variance from those already considered. Exhibit 2 tells a new story. The recording gauge was placed in service at 4 P. M. (E), and shortly afterward (A), the pressure began to fall. The jets grew dimmer and dimmer, while the Welsbach mantles became petticoats of red, with hems of white at the bottom. No wonder this man complains of ‘poor’ gas, while some learned friend, dropping in for an evening cigar, explains that there is ‘air in the pipes.’ The one consolatory reflection is that, at all events, the poor fellow had a good light to undress by (B to C).

Exhibits 3 and 4 come from my own residence. Together they form a ‘before-taking’ and ‘after-taking’ advertisement—not of medicine, but of a gas governor. The fact that I am located at a considerable distance—several miles—from the works, and am supplied through a main laid a number of years ago, when the territory was sparsely settled, enables me to present Exhibit 3. Comment on this record is unnecessary. After securing this diagram I installed a governor and set it at eleven tenths. Exhibit 4 shows what happened. I am now doing for myself, and at my own expense, that which the gas company fails to do for me. This governor, therefore, renders me almost entirely independent of the gas company; and, in order to demonstrate more clearly to what degree this independence extends, the gauge has been allowed to run for forty-eight hours without changing the card, thus super-imposing the record of the second day upon that of the first. Note how closely the readings for the two days agree. The governor is a protection against excess of pressure only; if the street pressure falls below eleven tenths—the point at which my governor is set—automatic regulation ceases, and my gas simply becomes subject to practically the same variations as exist on the main. Happily, the latter condition is infrequently realized in our neighborhood. No argument is needed to prove how successfully a governing device of this nature can cope with the trouble indicated by Exhibit 1, or how utterly inadequate it is to afford relief from the evil depicted in Exhibit 2. Increased pressure is the only remedy for the latter.

The gas company does not recommend the use of these house-to-house governors—presumably because such a recommendation would be in effect an admission that the service as now maintained by the company is not satisfactory. Indeed, the less enlightened officials—and it is these, unfortunately, with whom the consumer has generally to deal—positively and unreasoningly condemn all such regulating devices. In spite of this, there exist to-day several gas-reduction companies, whose sole occupation consists in exploiting various gas-pressure-regulating appliances, which are rented to consumers for a certain percentage of the monthly saving in the gas bills which their use effects.

It would appear to be a self-evident proposition that when one pays for gas delivered at his meter he is entitled to receive that gas under such a pressure as will afford the most satisfactory service. This pressure is found to be one inch. Making due allowance for reasonable fluctuations of a few tenths above the normal, any further departure from the standard may be taken as a sure indication of a disinclination on the part of the company to meet the expense of new pipes and regulating apparatus. The time is not far distant when the public will demand, not cheaper gas nor better gas, but a more satisfactory service. But before condemning the gas company one must look to his house piping. The company’s responsibility ends just inside the meter, and from that point the consumer must provide satisfactory appliances, giving the same attention to the gas pipes as he gives to the plumbing. This is seldom done and the company is frequently blamed for the neglect of the householder.

The gas engineer, steering between the Scylla of ‘poor’ gas and the Charybdis of excessive pressures, finds himself still ‘dangerous in the rapids’ of financial expenditure. At present he is doing the best he can with the money doled out to him by the management.

It will be observed that up to the present point the gas meter itself has played no part in the discussion. The meter, although greatly maligned, is in reality an eminently satisfactory piece of mechanism. Concerning this apparatus many erroneous notions prevail. One of these is that a householder may burn thousands of feet of gas without cost to himself, provided he keeps the company in blissful ignorance of the employment of gas for heating purposes upon his premises. The demonstration of the falsity of this idea lies within the reach of any one who will take the trouble to read his own meter on those days on which the company’s indexer pays his monthly visits.

Figs. 1, 2 and 3 represent different states of the index usually employed on the three, five and ten light meters, the sizes commonly found in our dwellings. The smaller dial, placed centrally above the other, is known as the ‘proving dial,’ and, being used merely for testing purposes, is not considered in reading the gas consumption. Although the index dials vary in nomenclature as well as in number, it is generally safe to consider that if the name is placed above the dial a complete revolution of the pointer is required to register the amount of gas indicated by the name; whereas if the name is placed below the dial each numbered division of the dial represents the amount corresponding to the name. If doubt still exists as to the value of each division of the lowest or right-hand dial, remember that no meter index is designed to read less than one hundred cubic feet for each division of the circle.

After one has indexed his own meter for a month or two he is in a position to begin checking the bills presented. The ‘present state of meter’ and the ‘previous state of meter’ are always specified, and the mere subtraction of the former from the latter gives the consumption. This is not invariably the case, however. After a meter has registered its maximum reading—100,000 in the smaller sizes—it passes over the zero point and begins to build up a new record. This happens at intervals as long as the apparatus is kept in service. Before me lies a bill giving the ‘present state’ as 1,700 and the ‘previous state’ as 96,300. Since the meter was continuously employed, it must have registered up to 100,000, so that it registered 3,700 cubic feet on the old score before recording 1,700 cubic feet on the new. Consequently, adding 1,700 to the difference between ‘previous state’ and the highest possible reading gives 5,400 cubic feet—the amount consumed during the month. By reading one’s own meter the detection of any error on the part of the indexer or of the clerical force at the gas office becomes possible. Errors of this nature are of rare occurrence, as those who have adopted this plan of checking gas bills will testify. The responsibility for excessive bills is thus taken from the gas employees and thrown entirely upon the gas-registering mechanism itself. Those people, then, who chuckle furtively over the fact that the gas company has not ‘caught on’ to the surreptitious use of gas ranges are either the fortunate possessors of ‘slow’ meters or are deluding themselves as to the amount of gas which they actually consume.

Fig. 4 is a photograph of the common dry meter, with the front, back, top and left side removed. It is called a ‘dry’ meter to distinguish it from those meters, having little vogue in this country, which employ a liquid in place of a valve motion. The apparatus shown consists of a case divided into three compartments by a horizontal partition one fourth of the way down from the top, and by a vertical partition centrally placed and extending upward from the bottom of the casing to the horizontal partition. The upper compartment contains the registering mechanism and a small valve chamber, the latter corresponding to the steam chest of an engine. In each of the lower compartments is a metal disk attached to the central partition by well-oiled flexible leathers, each disk, leather and the partition forming a bellows. As in a locomotive, the meter really consists of two separate mechanisms, set to operate out of phase and avoid dead centers.

Considering one mechanism only, recourse may be had to a diagrammatic representation of the action (Fig. 5). Gas entering the inlet passes into the valve chamber. Here an ordinary D-slide-valve closes two of the openings, leaving a third through which the gas may flow into the bellows or inner compartment. The bellows expands, gradually filling the outer compartment, and forcing the gas out under the valve into the outlet pipe, as indicated by the arrows. When the bellows is fully distended the valve shifts into the position shown in Fig. 6, admitting the inflowing gas to the outer compartment and collapsing the bellows, whose contents are forced into the outlet pipe by the paths traced by the arrows.

Thus, it will be observed, the meter is a volume measurer pure and simple, measuring cubic feet with as much deliberation as is required to deal water out of a cask by means of a pint dipper. Its percentage of error is the same at all pressures and under all loads within its capacity, and it measures cubic feet of gas regardless of whether that gas be expanded or compressed.

And so we are obliged to realize, as another fallacy is exposed, that the meter does not spin around most energetically under the higher pressures, cheerfully and accommodatingly serving its masters by adding a mythical cubic foot or two to the count at each revolution.

It remains, then, to consider the error of the meter. The custom is, in New York at least, not to set a meter that registers fast—that registers a greater volume of gas than actually passes through it. If it is found to be slow, however, and not more than three per cent., it is allowed to go out. As a result, the meter, when first placed, always favors the consumer, sometimes to the extent of recording only ninety-seven feet of gas for each one hundred feet actually passed. Owing to the aging of the mechanism and the drying out of the leathers, there exists a tendency to increase the registry for each cubic foot passed. In this way a slow meter may become a fast meter after a period of active service. From the meager data at my disposal, it would appear that every meter should be called in for a thorough overhauling and readjustment at periodic intervals of from three to five years.

Assuming that there are several million gas meters in Greater New York alone, it is but natural to expect that out of this vast number, in spite of any reasonable care that may have been exercised in their adjustment originally, many will be found subsequently to be defective—some because of mechanical injury, some through sheer old age. Unfortunately, it is not possible as yet to obtain a convincingly large array of figures; but in the Borough of Brooklyn, where there are in service nearly a quarter of a million meters, and where complaints against them have been studiously encouraged by the authorities, one hundred and eighty-seven meters have been carefully tested. Here are the results:

When one remembers that these one hundred and eighty-seven meters are presumably the worst of their kind, having been put in evidence by a naturally suspicious public, it is but fair to assume that the figures overrate rather than underestimate the errors of the average gas meter. Quoting from The Progressive Age, a journal devoted largely to the interests of the gas industry: “The meters made to-day will remain a long while in service before they begin to register incorrectly, and when we consider the dampness, extremes of temperature and hard usage they receive as they are transferred from cellar to attic, from among the dust, cobwebs and litter of a basement closet to the corner shelf of some coal cellar, to be the playground of rats, spiders and cockroaches, to be drenched in summer by sweating or leaky water pipes and wear a venerable beard of icicles in winter—to be, in fact, the worst-used machine about a gas plant—we can not fail but express surprise that it registers at all correctly.”

THE SUN’S DESTINATION.
By Professor HAROLD JACOBY,
COLUMBIA UNIVERSITY.

Three generations of men have come and gone since the Marquis de Laplace stood before the Academy of France and gave his demonstration of the permanent stability of our solar system. There was one significant fault in Newton’s superbly simple conception of an eternal law governing the world in which we live. The labors of mathematicians following him had shown that the planets must trace out paths in space whose form could be determined in advance with unerring certainty by the aid of Newton’s law of gravitation. But they proved just as conclusively that these planetary orbits, as they are called, could not maintain indefinitely the same shapes or positions. Slow indeed might be the changes they were destined to undergo; slow, but sure, with that sureness belonging to celestial science alone. And so men asked: Has this magnificent solar system been built upon a scale so grand, been put in operation subject to a law sublime in its very simplicity, only to change and change until at length it shall lose every semblance of its former self, and end perhaps in chaos or extinction?

Laplace was able to answer confidently: No. Nor was his answer couched in the enthusiastic language of unbalanced theorists who work by the aid of imagination alone. Based upon the irrefragable logic of correct mathematical reasoning, and clad in the sober garb of mathematical formulæ, his results carried conviction to men of science the world over. So was it demonstrated that changes in our solar system are surely at work, and shall continue for nearly countless ages; yet just as surely will they be reversed at last, and the system will tend to return again to its original form and condition. The objection that the Newtonian law meant ultimate dissolution of the world was thus destroyed by Laplace. From that day forward, the law of gravitation has been accepted as holding sway over all phenomena visible within our planetary world.

The intricacies of our own solar system being thus illumined, the restless activity of the human intellect was stimulated to search beyond for new problems and new mysteries. Even more fascinating than the movements of our sun and planets are all those questions that relate to the clustered stellar congeries hanging suspended within the deep blue vault of night. Does the same law of gravitation cast its magic spell over that hazy cloud of Pleiads, binding them, like ourselves, with bonds indissoluble? Who shall answer, yes or no? We can only say that astronomers have as yet but stepped upon the threshold of the universe, and fixed the telescope’s great eye upon that which is within.

Let us then begin by reminding the reader what is meant by that Newtonian law of gravitation. It appears all things possess the remarkable property of attracting or pulling each other. Newton declared that all substances, solid, liquid or even gaseous, from the massive cliff of rock down to the invisible air—all matter can no more help pulling than it can help existing. His law further formulates certain conditions governing the manner in which this gravitational attraction is exerted; but these are mere matters of detail; interest centers about the mysterious fact of attraction itself. How can one thing pull another with no connecting link through which the pull can act? Just here we touch the point that has never yet been explained. Nature withholds from science her ultimate secrets. They that have pondered longest, that have descended farthest of all men into the clear well of knowledge, have done so but to sound the depths beyond, never touching bottom.

This inability of ours to give a good physical explanation of gravitation has led numerous paradoxers to doubt or even deny that there is any such thing. But fortunately we have a simple laboratory experiment that helps us. Unexplained it may ever remain, but that there can be attraction between physical objects connected by no visible link is proved by the behavior of an ordinary magnet. Place a small piece of steel or iron near a magnetized bar, and it will at once be so strongly attracted that it will actually fly to the magnet. Any one who has seen this simple experiment can never again deny the possibility at least of the law of attraction as stated by Newton. Its possibility once admitted, the fact that it can predict the motions of all the planets, even shown to the minutest details, transforms the possibility of its birth into a certainty as strong as any human certainty can ever be.

But this demonstration of Newton’s law is limited strictly to the solar system itself. We may indeed reason by analogy, and take for granted that a law which holds within our immediate neighborhood is extremely likely to be true also of the entire visible universe. But men of science are loath to reason thus; and hence the fascination of researches in cosmic astronomy. Analogy points out the path. The astronomer is not slow to follow; but he seeks ever to establish upon incontrovertible evidence those truths which at first only his daring imagination had led him to half suspect. If we are to extend the law of gravitation to the utmost, we must be careful to consider the law itself in its most complete form. A heavenly body like the sun is often said to govern the motions of its family of planets; but such a statement is not strictly accurate. The governing body is no despot; ’tis an abject slave of law and order, as much as the tiniest of attendant planets. The action of gravitation is mutual, and no cosmic body can attract another without being itself in turn subject to that other’s gravitational action. If there were in our solar system but two bodies, sun and planet, we should find each one pursuing a path in space under the influence of the other’s attraction. These two paths or orbits would be oval, and if the sun and planet were equally massive, the orbits would be exactly alike, both in shape and size. But if the sun were far larger than the planet, the orbits would still be similar in form, but the one traversed by the larger body would be small. For it is not reasonable to expect a little planet to keep the big sun moving with a velocity as great as that derived by itself from the attraction of the larger orb. Whenever the preponderance of the larger body is extremely great, its orbit will be correspondingly insignificant in size. This is in fact the case with our own sun. So massive is it in comparison with the planets, that the orbit is too small to reveal its actual existence without the aid of our most refined instruments. The path traced out by the sun’s center would not fill a space as large as the sun’s own bulk. Nevertheless, true orbital motion is there.

So we may conclude that as a necessary consequence of the law of gravitation every object within the solar system is in motion. To say that planets revolve about the sun is to neglect as unimportant the small orbit of the sun itself. This may be sufficiently accurate for ordinary purposes; but it is unquestionably necessary to neglect no factor, however small, if we propose to extend our reasoning to a consideration of the stellar universe. For we shall then have to deal with systems in which the planets are of a size comparable with the sun; and in such systems all the orbits will also be of comparatively equal importance.

Mathematical analysis has derived another fact from discussion of the law of gravitation which perhaps transcends in simple grandeur everything we have as yet mentioned. It matters not how great may be the number of massive orbs threading their countless interlacing curved paths in space, there yet must be in every cosmic system one single point immovable. This point is called the Center of Gravity. If it should so happen that in the beginning of things, some particle of matter were situated at this center, then would that atom ever remain unmoved and imperturbable throughout all the successive vicissitudes of cosmic evolution. It is doubtful whether the mind of man can form a conception of anything grander than such an immovable atom within the mysterious intricacies of cosmic motion.

But in general, we can not suppose that the centers of gravity in the various stellar systems are really occupied by actual physical bodies. The center may be a mere mathematical point in space, situated among the several bodies composing the system, but nevertheless endowed with the same remarkable property of relative immobility.

Having thus defined the center of gravity in its relation to the constituent parts of any cosmic system, we can pass easily to its characteristic properties in connection with the inter-relation of stellar systems with one another. It can be proved mathematically that our solar system will pull upon distant stars just as though the sun and all the planets were concentrated into one vast sphere having its center in the center of gravity of the whole. It is this property of the center of gravity which makes it preëminently important in cosmic researches. For, while we know that center to be at rest relatively to all the planets in the system, it may, nevertheless, in its quality as a sort of concentrated essence of them all, be moving swiftly through space under the pull of distant stars. In that case, the attendant bodies will go with it—but they will pursue their evolutions within the system, all unconscious that the center of gravity is carrying them on a far wider circuit.

What is the nature of that circuit? This question has been for many years the subject of earnest study by the clearest minds among astronomers. The greatest difficulty in the way is the comparatively brief period during which men have been able to make astronomical observations of precision. Space and time are two conceptions that transcend the powers of definition possessed by any man. But we can at least form a notion of how vast is the extent of time, if we remember that the period covered by man’s written records is registered but as a single moment upon the great revolving dial of heaven’s dome. One hundred and fifty years have elapsed since James Bradley built the foundations of sidereal astronomy upon his masterly series of star-observations at the Royal Observatory of Greenwich, in England. Yet so slowly do the movements of the stars unroll themselves upon the firmament, that even to this day no one of them has been seen by men to trace out more than an infinitesimal fraction of its destined path through the voids of space.

Travelers upon a railroad can not tell at any given moment whether they are moving in a straight line, or whether the train is turning upon some curve of huge size. The St. Gothard railway has several so-called ‘corkscrew’ tunnels, within which the rails make a complete turn in a spiral, the train finally emerging from the tunnel at a point almost vertically over the entrance. In this way the train is lifted to a higher level. Passengers are wont to amuse themselves while in these tunnels by watching the needle of an ordinary pocket compass. This needle, of course, always points to the north; and as the train turns upon its curve, the needle will make a complete revolution. But the passenger could not know without the compass that the train was not moving in a perfectly straight line. Just so we passengers on the earth are unaware of the kind of path we are traversing, until, like the compass, the astronomer’s instruments shall reveal to us the truth.

But as we have seen, astronomical observations of precision have not as yet extended through a period of time corresponding to the few minutes during which the St. Gothard traveler watches the compass. We are still in the dark, and do not know as yet whether mankind shall last long enough upon the earth to see the compass needle make its revolution. We are compelled to believe that the motion in space of our sun is progressing upon a curved path; but so far as precise observations allow us to speak, we can but say that we have as yet moved through an infinitesimal element only of that mighty curve. However, we know the point upon the sky towards which this tiny element of our path is directed, and we have an approximate knowledge of the speed at which we move.

More than a century ago Sir William Herschel was able to fix roughly what we call the Apex of the sun’s way in space, or the point among the stars towards which that way is for the moment directed. We say for the moment, but we mean that moment of which Bradley saw the beginning in 1750, and upon whose end no man of those now living shall ever look. Herschel found that a comparison of old stellar observations seemed to indicate that the stars in a certain part of the sky were opening out, as it were, and that the constellations in the opposite part of the heavens seemed to be drawing in, or becoming smaller. There can be but one reasonable explanation of this. We must be moving towards that part of the sky where the stars are separating. Just so a man watching a regiment of soldiers approaching, will see at first only a confused body of men. But as they come nearer the individual soldiers will seem to separate, until at length each one is seen distinct from all the others.

Herschel fixed the position of the apex at a point in the constellation Hercules. The most recent investigations of Newcomb, published only a few months ago, have, on the whole, verified Herschel’s conclusions. With the intuitive power of rare genius, Herschel had been able to sift truth out of error. The observational data at his disposal would now be called rude, but they disclosed to the scrutiny of his acute understanding the germ of truth that was in them. Later investigators have increased the precision of our knowledge, until we can now say that the present direction of the solar motion is known within very narrow limits. A tiny circle might be drawn on the sky, to which an astronomer might point his hand and say: Yonder little circle contains the goal towards which the sun and planets are hastening to-day. Even the speed of this motion has been subjected to measurement, and found to be about ten miles per second.

The objective point and the rate of motion thus stated, exact science holds her peace. Here genuine knowledge stops; and we can proceed further only by the aid of that imagination which men of science need to curb at every moment. But let no one think that the sun will ever reach the so-called apex. To do so would mean cosmic motion upon a straight line, while every consideration of celestial mechanics points to motion upon a curve. When shall we turn sufficiently upon that curve to detect its bending? ’Tis a problem we must leave as a rich heritage to later generations that are to follow us. The visionary theorist’s notion of a great central sun, controlling our own sun’s way in space, must be dismissed as far too daring. But for such a central sun we may substitute a central center of gravity belonging to a great system of which our sun is but an insignificant member. Then we reach a conception that has lost nothing in the grandeur of its simplicity, and is yet in accord with the probabilities of sober mechanical science. We cease to be a lonely world, and stretch out the bonds of a common relationship to yonder stars within the firmament.