On Central-Station Power Supply. 479 
so obnoxious from an esthetic point of view, and.of the dan- 
gers and responsibility attending the use of steam boilers 
by unskilled persons: these being done away with or re- 
moved from the more crowded parts of the city. The pos- 
sibility of running air motors in the centre of the city, 
where a supply of water for condensing or even feed is 
extremely expensive, is an obvious advantage. 
The extreme handiness of the working medium and its 
suitability for use by technically unskilled attendants may 
be adverted to. In this respect the air motor bears away 
the palm frem the electric motor, the gas engine, and even 
the much-enduring steam engine, all of which require a 
certain modicum of knowledge or experience. The repair 
also of such a machine requires only a knowledge of per- 
fectly well understood mechanical details. 
The use of the exhaust for either refrigeration, ventil- 
ation or even heating renders the rejected air a beneficial 
by-product instead of a nuisance, as the exhaust from a 
steam engine certainly is in summer. 
The suitability of compressed air for the working of lifts 
ought not to escape mention; a cheapening of the first cost 
by at least 10 per cent. and of running expenses at the rate 
of 75 over other systems can be easily attained. 
Tram cars worked by compressed air are now in use in 
Nantes, Brussels. Chester and other places; they have there 
proved both serviceable and economical, in spite of the fact 
that the power they use is generated in small compressing 
stations. A reservoir capacity with air at perfectly safe 
pressures can be obtained with an ordinary sized car to do 
a return journey of five miles without any intermediate 
charging station; and the consequent removal of a danger- 
ous overhead wire, such as is used on the electric trolly 
system, is not to be despised in a populous city. The 
difficulty of snow could be overcome by having a car 
devoted to clearing the tracks alone; but this will be pre- 
ferably effected by having a light overhead railroad, as the 
ruts in the streets caused by keeping a clean tramroad in 
