THE EXHIBITION OP 1862. 
143 
as exhibited by the different makers, showing the space they 
occupy in the ship, length of cranks, &c., as per sketch, taken 
from Mr. Mallet's report in the Practical Mechanics’ Journal . 
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No. l. 
No. 2. 
No. 3. 
No. A. 
From the above it will be seen that No. 1, with the double 
piston-rod and reversed connecting-rod, occupies the least 
space in length; No. 3, with a three-crank connecting-rod, the 
next ; and subsequently follows No. 2, trunk engine, in the 
order of length ; and, lastly. No. 4. Mr. Mallet classes them 
differently by taking the crank as the unit of measure ; from 
which it follows, that the direct-acting engine, with short con- 
necting-rod, occupies a much less total length than either of 
the others. This saving of space on board ship is always a 
desideratum in the construction of marine engines, and is a 
point carefully attended to in the British navy. 
Most of the engines are of the screw-propeller kind, and 
