In a recent number of the Journal we touched on the various methods of transmission of power, and showed how steam had been laid on in mains in the streets of American towns, and a house-to-house distribution thus effected. Loss has been found, however, to result from leakage and condensation, and these defects have militated against the system. Water under pressure has obtained extended application in this country where power was required in docks and warehouses; but up to the present time, a motor has not been introduced satisfying the necessary requirements of economy sufficiently to render the system of commercial value for supplying small power either for domestic purposes or to the lesser industries. Bursting of pipes, through frost or other cause, might result in serious damage, moreover, in dwelling-houses.

The problem of transmission of power may possibly find a solution in electricity in the future; but as regards the present, suffice it to say that the cost of production of such agency entirely precludes it from entering into the field of competition. Attempts now being made, in Paris and Birmingham, to distribute power by rarefied air in the former, and by compressed air in the latter city, possess no slight interest. In each case, the method adopted differs in no way in principle from that of the systems already touched on. Central pumping stations, furnished with boiler and steam-power, supply the requisite energy; whilst the transmitting medium—steam, water, or air, as the case may be—is distributed through the principal mains, which feed in their turn the lesser arteries of the system supplying the individual consumer.

In the case of rarefied air, though, theoretically, a pressure of fifteen pounds per square inch could be obtained, in practice it is found advisable to work at a pressure of about ten pounds, without approaching nearer to an absolute vacuum. Three classes of motors are employed to convert the vacuum in the mains into useful work; suffice it to say, however, that whilst differing in the details of construction, the principle involved throughout is the same, and consists essentially of modifications of the steam-engine to the requirements of air-pressure. Payment is made according to the power absorbed by each consumer, an ingenious arrangement actuating as counter, indicating how much work is actually done, irrespective of the number of revolutions made by the motor. Even where gas is available, the cost of engines for using it has not unfrequently militated against its adoption by the smaller industries; hence the Parisian Company for the distribution of power by rarefied air has elected not only to supply power but to lease out the motors as well. Their customers embrace such users of small power as hat-block makers, jewellers, wood-turners, comb-cutters, stay and clothing manufacturers, dentists, butchers, &c. The cleanliness of this system, and its excellent ventilating capabilities, should form an argument in its favour. Not only is all smell from combustion, as in the case of the gas-engine, avoided, but, by drawing at every stroke a given quantity of air from the room, the motor directly produces ventilation.

Time alone can show whether the system will prove a commercial success; in any case, its promoters could hardly have chosen a better field for its introduction than Paris, a city containing upwards of a million persons engaged in the minor industries already indicated, and which require small motive power.