"Second, the bulk of steam compared with that of water.
"Third, the quantity of water evaporated in a certain boiler by a pound of coals.
"Fourth, 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.
"Fifth, how much water in the form of steam was required every stroke by a small Newcomen's engine, with a wooden cylinder six inches diameter, and twelve inches stroke.
"Sixth, the quantity of cold water required in every stroke to condense the steam in that cylinder, so as to give 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 of water in the form of steam; and I accordingly applied to Dr. Black, 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 [Pg096] evaporated by the boiler, and used by the cylinder, was known, and in determining, 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 established fact, that 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 every stroke to below that heat."
LOCH LOMOND.