36 Mr. Davies Gilbert's observations on the steam engine. 
40 of Fahrenheit above 212 0 doubles the steam's elastic 
lorce, and that 30° more treble it ; great expectations were 
consequently formed of the increased power that would be 
obtained, from a given consumption of fuel, by using high 
pressure steam ; but the following most important circum- 
stances were overlooked, till experience forced them into view. 
That the temperature of steam cannot be raised, with a 
speed suited to mechanical purposes, in any other way than 
through the medium of its generating water. 
And that water heated above 212 0 sends off more steam, 
with a proportionate absorption of latent heat, increasing the 
density of the steam previously generated of atmospheric 
elasticity, thus doubling its power at 212 0 -|- 40 0 ; but at an 
expense of fuel, not much inferior to the power gained. 
If steam could be heated, as an independent elastic fluid, ex- 
panding 4I0 th of its bulk for each degree of Fah.; and if its ca- 
pacity were the same as the capacity of water, a quantity of heat, 
equal to that rendered latent, would raise the power from unity 
g, v900 
to ~-j = 6 \. If the capacities of steam and water, according 
to some recent experiments, be as 1,55 to 1, the increase of 
900 
power will be from unity to ■—) 1,5 °— 31 But the non-con- 
ducting property, common to all elastic fluids, has hitherto 
prevented this advantage from being obtained. Heated 
through the medium of its generating water, high pressure 
steam is believed however to be advantageous ; and by its 
means additional power may be obtained, when an increase 
is requisite for any temporary use. 
A contrivance has recently been attempted, by which a 
given small quantity of water is forced into a minute boiler at 
each stroke of the engine, and the boiler, presenting a very 
large surface in proportion to its content, is kept at an equa- 
ble high temperature by immersion in a fuzed metal. Thus 
great degrees of elasticity and of rarity may be combined ; 
