Prof. Barnard on a modification of the Ericsson Engine. 249 
+4 1 wVAY—1)  4(1—p 7-1) 
P=15al 4 (2—-1)+ “a See snd 1] 
If, in this, we put 4=-8, we shall obtain P=3-69a=81550 lbs., 
or 296 horse power. 
With 4=%, we have P=3-38a=74700 lbs., or 271 horse power. 
It thus appears, that, when m and m are equal, the variation is 
slow below J or m==8. But the uniformity of action is in favor 
of the higher numbers. 
In the expression above, at its maximum value, 
} 
-1 =| 
i= (Co +" = 71226. 
uy 
But the value of P is hardly perceptibly greater at this point, 
than for some distance on either side of it. 
The comparison of these results, however, with those which 
may be obtained by making m greater than /, will show that it is 
not true economy to make these two numbers equal. If m be 
put=75, while / remains=%, the power will ascend to 4-415a= 
97570 \bs., which, supposing two revolutions and six feet stroke 
_as before, gives a horse-power of 354. Putting m =°85, an 
2, the pressure becomes 4:92a= 108700 lbs. =395 horse-power. 
Values of Z and m like these cannot possibly be employed with 
advantage in an engine constructed on the plan of Ericsson’s ; 
since they would render the action almost spasmodic in character. 
and reduce the minimum power of the pair of connected engines 
below zero. We have seen that a cut-off was actually used in 
the ship, which was considerably less than %; but it is very evi- 
dent the defects of the machinery prevented the attainment of 
the tension due to such a cut-off; which, therefore, failing to 
secure the advantage aimed at, failed also to make the evil very 
conspicuously manifest. But this evil is sure to occur, and is 
likely to interfere seriously with, if not completely to counteract, 
the advantages presented by this means of gaining power, just 1n 
proportion as leakage is stopped, or other causes which may keep 
down the tension are removed. 
The construction now proposed will be, in a great manner, 
free from these disadvantages ; and hence the powers last stated, 
ranging from 350 to 400, are obtainable without difficulty. Such 
powers are more than sufficient, according to the investigations 
of Prof. Norton, to make these engines available for purposes of 
speed in ocean navigation. 
Nor are these increments of power accompanying enlargement 
of supply cylinder, attended with an economical disadvantage. 
If we compare the powers on the two suppositions, /=3, m=, 
and 1=%, m=, we shall see that, while, in the latter case, the 
power is increased 30 per cent, the volume of air to be heated is 
Szconp Serres, Vol. XVI, No. 47.—Sept, 1853. 32 
