212 Report on Miscellaneous Implements at Newcastle. 
piston clears the cylinder of the products of combustion. The speed is 
governed, as in the Gas Engine, by cutting off the supply of oil when the 
engine is running too fast, and readmitting it when she falls below the 
proper number of revolutions. 
An experimental test of Spiel's engine, made by Dr. Hop- 
kinson, F.R.S., seems to demonstrate that, with oil at Id. a 
Fig. 1 2.— The " Essex " Steam Boiler. 
[See p. 213.] 
gallon, the cost of fuel would be about \\d. per horse-power per 
hour. This is somewhat more than the cost of fuel in a gas 
engine, but where small motors, doiug intermittent duty, are 
