Mr. Davies Gilbert’s observations on the steam engine. 33 
14 cubic feet of water may be converted into steam, by that 
given consumption of fuel, occupying about 1330 times more 
space than the water from which it was produced. The whole 
space therefore filled by the steam amounts to 18620 cubic 
feet, capable of containing F150410 pounds of water; and 
as 30 inches of mercury at a specific gravity of 13.568 cor- 
respond to a column of water 33-92 feet in length, through 
this space the i'i 50410 pounds of water may be supposed to 
be raised when a vacuum is formed, giving an efficiency of 
39^361000, or above thirty nine millions of pounds raised one 
foot high. 
But when this power of steam is applied through the 
medium of a piston, acting in the cylinder of a steam engine, 
large deductions must be made to arrive at the practical duty. 
The air pump is usually constructed of a size to require 
about one eighth part of the efficiency ; 
Some imperfection in the vacuum cannot be avoided ; 
And friction must exist to a considerable amount where 
bodies in motion have to confine an elastic vapour, ready to 
escape through the smallest aperture. So that thirty millions 
would probably have exceeded the attainable limit of duty, 
but for two expedients : 
First. Causing the steam to act expansively, after exerting 
its whole force through a certain part of the cylinder ; and 
Secondly. Raising the temperature much above 212 0 of 
Fahrenheit, and thereby communicating to the steam a power 
beyond what is termed atmospheric strength ; but this is, of 
course, accompanied by an additional expenditure of fuel. 
The plan of working expansively is founded on the follow- 
ing investigation. 
mdcccxxvii, F 
