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.