154 Prof. Barnard on the Elastic Force of Heated Air. 
economically much superior to the steam engine.* One of these, 
Mr. Joule, has even published an outline of a plan which he 
would adopt in order to secure the advantages to be attained by 
the use of this motive power ;} and he has shown, by the appli- 
cation of the convenient formula of Prof. Thompson, for deter- 
mining what fraction of the heat expended is converted into 
power by thermo-dynamic engines, that an engine constructed on 
his plan would produce an amount of mechanical efiect greater 
in the ratio of 6 to 5 than a condensing steam engine with four- 
teen atmospheres of pressure in the boiler, and sin which the 
steam expands itself in the cylinder to the temperature of 80°. 
Compared with steam expanding in like manner from the press 
ure of a atmospheres, the economy would be nearly as 3 to 2; 
and taking the steam at the original pressure of two atmospheres 
it would be almost as 2 to 1(L: 18). But in these computa- 
tions, the expansion of steam in the cylinder is presumed to carry 
the temperature down to 80°, a condition never fulfilled 1 in aes 
gine as 34 to 1. And if we compare it with a non- eee 
engine at two atmospheres, we shall find that the air engine 
would be mee times and upward superior to the other in point 
of econom 
In all she discussions. which the engines. ok Capt. Ericsson 
have provoked, certain propositions, which are rendered true by 
stroke, there te in the natur Sex be a great waste of 
heat, — the ide of the he aoe air. 
be too and too Penervs be well suited ie rapid we cs tt 
may nevertheless be yoo great advantage in driving machinery or serving 
and Ed. Phil. Phil Mag. Jan, 1868; and Phil. Trae, 1868, Pat T 
