upon the BtemuEnghu, $ 
It was also known, that evaporation caused the cooling of the 
evaporating liquid, and bodies in contact with it. 
I had myself made experiments to determine the following 
facts. 
l<Sif, The capacities for heat of iron, copper, and some sorts of 
wood, comparatively with water. Similar experiments had also 
subsequently been made by Dr Irvine, on these and other me^? 
tals. 
The bulk of steam was compared \nth that of water. 
Sdy The quantity of water which could be evaporated in a 
certain boiler by a pound of coals. 
4ifh, The elasticities of steam at various temperatures greater 
than that of boiling water, and an approximation to the law 
which it followed at other temperatures. 
5^7^, How much water, in the form of steam, was required 
every stroke by a small Newcomen’s engine, with a wooden cy-^ 
linder ax inches diameter, and twelve inches^ long -in the 
stroke. 
6th, I had measured the quantity of cold water required in 
every stroke to condense the steam in that cylinder, so as to ^ve 
it a working power of about 7 lb. on the inch. 
Here I was at a loss to understand how so much cold water 
could be heated so much by so small a quantity in the form of 
Steam, and applied to Dr Blacky and then first understood what 
was called Latent Heat. 
But this theory, though useful in determining the quantity of 
injection necessary where the quantity of water evaporated by 
the boiler, and used by the cylinder, was known, and in deter- 
mining, by the quantity and heat of the hot water emitted by 
Newcomen’s engines, the quantity of steam required to work 
them, did not lead to the improvements I afterwards made in 
the engine. These improvements proceeded upon the old-esta- 
blished fact, tiiat steam was condensed by the contact of cold 
bodies, and the later known one, that water boiled in vacuo at 
heats below 100°, and consequently that a vacuum could not 
be obtained unless the cylinder and its contents were cooled eve- 
ry stroke to below that heat. 
These, and the degree of knowledge I possessed of the elas^ 
tjcities of steam at various heats, were the principal things it wa^ 
