232 Prof. Barnard on a modification of the Ericsson Engine. 
Art. XXVI.—Proposed Modification of the construction of the 
Ericsson Engine, with a view to increase its available power ; 
by Frepericx A. P. Barnarp, Professor of Chemistry and 
Natural History in the University of Alabama. 
The deep interest with which the public have regarded the 
recent attempt of Capt. Ericsson to employ the elastic force of 
air expanded by heat, for the propulsion of vessels at sea, appears 
to have given place to a feeling almost of disappointment. What- 
ever hopes might still have been entertained by observers whose 
opinions are governed by visible results only, and not by theoretic 
deductions, of the practicability of attaining a materially higher 
degree of power with greater experience, such anticipations can 
hardly be indulged with any confidence by those who have read 
with attention the searching examination of the performance of 
the experimental engines of the “ Ericsson” ship, made by Prof. 
Norton, in the last number of this Journal. 
f, in connection with the article of Prof. Norton, we refer to 
the theoretic investigation of the general question by Major Bar- 
nard, of the U. S. Engineers, in the April number of Appleton’s 
Mechanics’ Magazine, we shall be satisfied that there are difficul- 
ties in the way of increasing the efficiency of the engine in its 
present form, too serious to be easily surmounted. As to the fact 
that it has not yet been brought up nor nearly up, to the 
original estimate of the inventor, no doubt can possibly be enter- 
tained in any quarter. . 
Taking the engine in its present form, there appear to be three 
modes, and only three, by which its power may be increased ; 
and all these are attended by practical disadvantages of such a 
nature as greatly to limit their availability. The first is, ob- 
viously, to increase its size; but, in so doing, we increase the 
weight proportionally, and thus unfit the engine for the uses of 
locomotion. The second, is to enlarge the supply cylinder only, 
increasing the quantity of air employed at each stroke; but this, 
besides requiring a similarly increased amount of fuel, necessarily 
increases rapidly the irregularity, or rather, inequality of action 
of the driving power, at different periods of the stroke. The 
third mode, isto diminish the fractional part of the stroke during 
which the air is admitted to the working cylinder, or to place the 
cut-off earlier in the stroke. But here a practical limit very 
shortly presents itself, in the occurrence of a resistance towar 
the close of the stroke, superior to the pressure on the working 
piston. With double engines connected as are those of the 
“ Briesson,” such a resistance is not inadmissible within certain 
imits; because the negative pressure in either engine may be 
overcome by the positive power of the other; but even with such 
