“ 
Prof. Barnard on the Elastic Force of Heated Air. 163 
effectual methods of roe the evil may be devised by ingen- 
ious mechanics, I have no doubt. Upon this point I shall pres- 
ently have something more to say. 
s it is perhaps too much to expect that the air engine will ever 
Ye wnictoant lly employed to propel the largest ships, on account 
its weight and bulk, it is obvious that the effective pressures 
which we have already seen are considerable, may be materially 
increased by resorting to the expedient which Capt. Ericsson is 
said to have adopted in his engines now in process of construc- 
tion, of employing air which has been previously condensed in a 
suitable chamber to such a pressure as may be thought expedient, 
A double density only, given to such a confined mass, might fu fur- 
nish to the engine a mean effective pressure of more than twenty 
pounds; whereas not more than three or four at the outside are 
attainable in the engines of the ‘ Ericsson,” and only between 
two or three appear to have been attaine 
It follows of course that engines worked on the principle of 
in er July number ‘of hues s pd e, by ‘ia neal an 
pansion of the top and bottom of the working cylinders. 
I have observed that the working temperature assumed by Mr. 
Joule is higher than is necessary. It remains to consider what 
* Still, I cannot but think that the leakage has nel ees a and that the 
ck of power which has been to such a degree imput o this cause, has resulted 
from the impossibility of heating the air by the contrivances bite ie ed in the aban- 
doned engines. The idea that “the regenerators were e the principal source of 
heat” led to me ee eg of furnace arrangements viandhuelly uae, IS to the 
eae — n them 
every stroke. t 10 revihakiods am inute, wo 40° 95 ¢ 
Now the velocity with which air under pressure escapes into the per tlt ard is rep- 
ion 
viavV B'-P 
p’ 
in which v is the Hoge hs beep which the atmospheric 
(= 1299 ft. des ) P e elastic force of the confined s air, rand iP gore of the Ps 
mosphere. h Z, gies ain in the case in hand, v’ = 765 «hes nches, 
And 40-95 eu. ft. Sabai 70761 cubic inches, which would ala an apert 
to wear sq. inches to admit of their escape in one second. Such we as 
this is incredible. Maj. ‘Barmard Lhgrision Mie July, ee reo the so." 
e to +}, , which is still 11-373 cu. in. per sec—equal to @ escape from 
in the reservoir of one of his engines, 
