Up to recent years there was no reason for putting the question that
forms the title of this article, for it was admitted by all that the
conversion of thermic energy, or heat produced by the combustion of
coal, into mechanical energy or work could no longer be effected
economically except by having recourse to steam. In ordinary language,
and even to manufacturers, steam engine was the equivalent of thermic
motor, and it would not have occurred to any one to use anything else
but steam to effect the transformation.
The progress that has been made during the last twenty years in the
thermatic study and construction of gas motors (without speaking of hot
air motors) has shown that the use of steam is not absolutely
indispensable for the production of work, and it has demonstrated that,
as regards dynamic product, the gas motor preserves the advantage,
although the relatively high price of the illuminating gas employed in
the production of the motive power generally renders the use of this
combustible more costly than steam, especially for high powers.
The economic truth of twenty years ago, when gas motors absorbed 1,500
liters per horse hour and exceeded with difficulty an effective power of
from 8 to 10 horses, has become less and less certain, when the
consumption has successively descended to 1,200, 1,000, 800 and even to
600 liters of gas per horse hour, the power of the motors rising
gradually to 25, 50 and 100 horses with a motor having a single cylinder
of a diameter of 57 centimeters.
[Illustration: FIG. 1.--CORLISS ENGINE AND BOILER OF 100 INDICATED
H.P.--ELEVATION AND PLAN.