AT4 Canadian Record of Science. 
power by means of air under pressure, the chief parts are: 
the source of power, the prime mover, the air-compressor; 
the air reservoir and mains, the distributing pipes, the pre- 
heaters, and the motors. 
Source of power.—This may be either a waterfall or simply 
coal. So long as coal retains its present position as the 
cheapest vehicle of energy we possess, our cataracts and 
rapids must continue to occupy the secondry place as cheap 
sources of power. This is due to the fact that the interest 
on the first cost of the plant necessary to intercept, as it were, 
the power from the falling water and to transmit it to the 
required locality is usually greater than the annual outlay 
due to capital expended on boilers and engines and the 
price of coal used. The cost per annum per horse-power 
delivered by a turbine (for the dam, hc¢ad- and tail-races, 
penstocks, gates and wheel-pit) varies from $2.00 to $25.08, 
according to the height of the water-fall impounded. On 
the other hand, the sum of $20.00 will amply cover the cost 
per annum of one horse-power delivered by a large steam 
engine. The difference between these figures, varying from 
$18.00 to $5.00 per horse-power, is what remains available 
to cover the expense of transforming the power at the 
water supply into a form suitable for transmission, for its 
subsequent conveyances, and for its retransformation into 
mechanical work at the point where it is required to be 
employed. The interest on the capital outlay and running 
expeuses of any such transmission system usually exceeds 
the balance above shown available, a.d allows the steam 
engine to win the race. 
The great transmitters of energy are, indeed, our railways 
and steamships, which transport, at a rate vastly cheaper 
than by any other means, the enormous stores of mechanical 
energy accumulated in our coal fields; and that in any 
amount and to any distance, unhampered by the losses of 
“power which inevitably accompany every transportation. 
Prime-movers.—When water is the source of power the 
prime-moyer is a turbine, which is turned by either the 
