140 
POPULAR SCIENCE REVIEW. 
understood; and is in almost every case resorted to, witli a 
great saving of fuel. Of late years the principle of expansive 
working was very imperfectly understood, and the result of its 
introduction was an immense economy ; for more than double 
the quantity of work is now done with the same quantity of 
fuel, of what was formerly accomplished on the old non-expan- 
si ve principle. It must, however, be borne in mind, that this 
cannot be effected without an increase of the pressure of steam, 
and hence follows the necessity of having the boilers of in- 
creased strength and improved construction. The neglect of 
these precautions has resulted in serious and fatal accidents, 
attended with a considerable loss of life and property. 
Irrespective of increased pressure, and working the steam 
expansively, the speed of the engine has been increased about 
one-third since the days of Watt. In his time the piston of 
the stationary engine travelled at the rate of 240 feet per minute; 
now it averages from 300 to 320 feet, and this, combined 
with high-pressure steam worked expansively, increases the 
power of the engine, in some cases, upwards of twofold, and, as 
already stated, doubles the quantity of work done with the 
same quantity of fuel. Thus an important saving is effected 
to tins and every other country where steam is employed as an 
agent of power and motive force. 
Having ushered in our observations with these necessarily 
technical remarks, we may state that the Exhibition of this 
year does not present any new nor original conception in the 
construction of stationary engines, with the exception of the 
non-condensing- engines, which, in this case, have their cylinders 
horizontal instead of vertical, as exhibited in the old construc- 
tion. There are some advantages in this, as the cylinders of 
the non-condensing engines are comparatively small, and are 
less liable to wear oval than would be the case in the large con- 
densing engines. These engines are, however, chiefly used as 
assistants to the stationary condensing engine, and effect a 
saving by the steam being employed twice over, for it first 
propels the piston of the high-pressure horizontal engine, after 
which it is conveyed to the cylinder of the large condensing 
engine, where it finishes the work at a considerably reduced 
pressure. 
These double engines are mere substitutes for the com- 
pound engine of Woolf,* with this disadvantage, that con- 
siderable loss is sustained by condensation in the transfer 
from one engine to the other ; and taking into account 
the back pressure and other causes, this combination is less 
effective than the united compound engine. But exclusive of 
Woolf is the inventor of the double-cylinder engine. 
