244 Prof. Barnard on a modification of the Ericsson Engine. 
demand for heat. T'o avoid protracting this discussion, this 
whole subject is reserved for future consideration. 
In regard to the power actually developed by the engines of 
the “Ericsson” ship, it is much below what, from the data, 
might have been expected. The inventor was justified in believ- 
to a deficient heating power. It seems impossible to ascribe it 
wholly to leakage. It is worth consideration, whether, after all, 
it is not ina great degree a consequence of the expenditure of 
much of the force developed, upon a portion of the stroke where 
it acts at the highest mechanical disadvantage ; and of another 
portion, in the mutual aid which these engines are required to 
furnish each other, after their power has become very much re- 
duced, and when they are precisely in the position in which they 
ought to act most efficiently. 
One advantage which must result from the adoption of the im- 
provement which it is the object of this paper to propose, has not 
thus far been alluded to. It consists in the unintermitting and 
uniform flow of the supply of condensed air into the reservoir.* 
As a consequence of this fact, indeed, we may be enabled to 
dispense with a reservoir almost entirely, without increasing the 
disadvantge of a perceptible fluctuation in the pressure on the 
working pistons. 
Thus far no notice has been taken of the important fact, that 
the temperature of the air which is driven into the reservoir by 
the supply cylinder, is very materially changed by the compression 
to which it is subjected. This circumstance cannot but exert an 
important influence on the working of the engine. Bui as yet 
nothing which has been written on this subject, and which has 
fallen under the notice of the present writer, has touched this 
t. 
material poin 
should be the legitimate influence of heat developed by compres- 
sion, and to modify the formule used in completing power, so as 
to allow for that influenee. Hitherto the tension of the com- 
is constant. But, in double engines, employing but a single reservoir, this fluctuation 
will nearly disappear. It is evident that the pressure might be rendered absolutely 
constant, if the case required it, by means of a large piston working in a cylinder at- 
: Pay ages weighted to the exacted pressure required 
trivance similar to this is employed to equalize the blast of tub-bellows in furnaces. _ 
F brous and undesirable attach- 
‘or a locomotive engine, however, it would be a cumbro 
ment. 
