Prof. Barnard on the Elastic Force of Heated Air. 167 
If however, we adopt the higher temperature of 626° F. to 
which there is as yet no well established objection, we may ob- 
tain an equal power with much smaller cylinders. The tables 
show that it is practicable to obtain nearly 9 pounds of available 
mean pressure under this temperature, when working only against 
the atmosphere ; and this moreover with an economy which, 
though not absolutely the highest, is considerably higher than any 
that is attainable under a lower temperature, and nearly two and 
a half times —— to that of steam of five atmospheres. Now 
if we compress air into the air chamber to the extent of five at- 
mospheres, and als two cylinders of each set against this pres- 
sure, while the third works against the atmosphere alone, we shall 
require no larger diameter than 45 inches for each of our cylin- 
ders to enable. us to obtain 1750 horse power, which is equal to 
that of a first class steamer. If then we increase the diameter to 
48 inches, we shall have more than 2000 aggregate horse pow- 
er, which enables us to allow nearly a sixth part for friction and 
other drawbacks.* The weight of the cylinders themselves will 
no longer be an objection. That of the air-chamber, heaters and 
refrigerators may be a more serious matter ; how far it wilf be so 
ocean steamers 7 
In making these estimates of power, I have not overlooked the 
manner in which the velocity of the piston is controlled by the 
increased or diminished resistance, as pointed out by Maj. Barnard 
in Appleton’s Magazine ‘for October. It will be found, upon the 
principles of estimate adopted by hi. that too low rather than 
too high a velocity of piston is here assumed. I admit ine con- 
clusiveness of all that Maj. Barnard has said in regard to the in- 
sufficiency of the original Ericsson engines to perform the task 
* Tfagain all these cylinders work against the reservoir, 38 inches will be as large 
a diameter as is necessary, and 40 inches will afford nearly 200 horse power surplus. 
+ All the estimates of power salty in this paper have been founded on suppositions 
pressure ich no serious objection can be take as the power is always 
directly as the pressure in the air chamber, there is plainly no limit to its increase 
except the rials. The question of mpactness is also de- 
ndent upon the same considerations. With a pres 0 atmospheres in the 
air ch a single twenty-inch cylinder (the other suppositions remaming as m h 
text) would give 300 horse power; and a forty-inch, . Two thirty-six inch cyl- 
eg would give 1950 horse oh cds more than enough to drive the Jar rgest ocean- 
ture o er. 
Two six-foot cylinders “would sfarish equal power with but five peers ospheres of 
pressure in the air-chamber. om themselves would have to are a 
pressure of more than twenty pragcn ti eres. These are the dimensions adopt by 
oes 
them also less, (as it must te so long as it is proposed to make the regenerators of 
id use,) the — which th engines will develope mnst be co 
re considered and compared wi with the lead gin nn a 
lished in the last number of this Journal. 
