156 Prof. Barnard on the Elastic Force of Heated Air. 
But, if we draw our supplies from the atmosphere directly, a 
very moderate pressure as compared with what is often employed 
with steam, will throw the regenerator entirely out of the ques- 
tion. ‘Taking the supply cylinder at two-thirds the working cyl- 
inder, as in Ericsson’s engines, supposing the external tem pera- 
ture to be 60°, and assuming that the tension of the air at the end 
of the stroke is, as economy requires, no higher than that of the 
atmosphere, the temperature at discharge is found by simple cal- 
culation to be 3199-5 F. Now air at 60° F. and density 1; will, 
on compression to density 2692, be raised to this same tempera- 
ture, and will have an elasticity of almost exactly four atmos- 
heres. An Ericsson engine working with this pressure would 
derive no advantage from a regenerator. And it is furthermore - 
evident that any approach to this limit must render the regenera- 
tor of no practical value. When, in addition to this, we take 
into consideration the imperfect manner in which this contrivance 
oes its work, the degree to which its numerous meshes of wire 
make 1, (the temperature of discharge) equal to 1’ (that of compression), and observe 
foe, ‘ 
7- It 2-2 
that atl, and Yo(T) (7) 
we shall have the equation, 
Ok 
wi ==") 7 
1 
Fred pra 
Whence I=(J,m a ¢ 
which is the value of % as shown further on, at the Maximum of power. The re- 
erator, therefore becomes useless, when the engine is producing the greatest ef 
eat sup- 
, & mai larger proportion of the heat su 
plied, is com erted into useful labor, than when a lower pressure te weed 
