478 Canadian Record of Science. 
that a higher degree of heating than is necessary merely to 
keep the exhausting air at atmopheric temperature is very 
conducive to economic working, as it can be effected at an 
insignificant cost. 
The pre-heaters used in Paris for this purpose are tiny 
little stoves, requiring an insensible amount of fuel and 
almost no attention. 
Notwithstanding this, the air delivered to motors, although 
at the same pressure, is 80 much increased in volume and 
temperature that all the losses due to leakage, friction and 
inefficiency of the operating machinery can be entirely 
wiped out at an additional expenditure almost infinitesimal, 
and without increasing the complexity or working diffi- 
culties of the system. . 
The air motors may be simply old steam engines, no 
alteration being necessary except the putting of them in 
good repair. lf the motors are specially designed for use 
with air, instead of steam, better results will, of course, be 
obtained ; and this is above all the case with the smallest 
sizes. For the larger sizes, however, a consumer who 
wishes to change from steam to air has only to discard his 
boiler, discharge his fireman, and couple his. steam pipe to 
the compressed air main. 
Turning to the commercial feasibility of a scheme for the 
supply of power by means of compressed air in a large in- 
dustrial centre, the author has estimated that a Centrat 
Station Power Supply Company could, in a city like Mont- 
real, supply to consumers, whether large or small, sufficient 
air to generate one horse power on their motor-brakes for 
$24.00 per annum; and secure at the same time 10 per 
cent. interest on their capital outlay. The price now paid 
for power by small cousumers ranges froin $60.00 to $120.00 
per annum, and is never less than $50.00. 
Reference may now be made to many advantages, apart 
from the question of cost, which attend the adoption of the 
pneumatic system. 
In the first rank we may place the elimination of 95 per 
cent: of the smoke which now renders manufacturing centres 
a 
a A 
