In 1775 Watt was sent to London to a mathematical instrument maker, but could not stay on account of his health, and soon afterwards came back to Glasgow.  He then got rooms in the College, and was made mathematical instrument maker to the University, and he afterwards opened a shop in the town.  He was but twenty-one years of age when he was appointed to this post in the College, and his shop became the lounge of the clever and the scientific.  The first time that his attention was directed to the agency of steam as a power was in 1734, when a friend of his, Mr. Robinson, who had some idea of steam carriages, consulted him on the subject,—­little is said of this, however.  In 1762 Watt tried some experiments on high-pressure steam, and made a model to show how motion could be obtained from that power; but did not pursue his experiments on account of the supposed danger of such pressure.  He next had a model of Newcomen’s engine, which would not work well, sent him to repair.  Watt soon found out its faults, and made it work as it should do.  This did not satisfy him, and setting his active mind to work, he found in the model that the steam which raised the piston had of course to be got rid of.  This, as a natural consequence, caused great loss of heat, as the cylinder had to be cooled so as to condense the steam; and this led him at last, after various plans, to adopt a separate vessel to condense this steam.  Of course, if you wish to save fuel, it is necessary that the steam should enter a heated cylinder or other vessel, or else all the steam is lost,—­or in other words, condensed,—­that enters it, until it has from its own heat imparted so much to the cylinder as to raise it to its own temperature, when it will no longer condense, and not till then does it begin to exert its elastic power to produce motion.  This was the great object gained by James Watt, when, after various experiments, he gave up the idea altogether of condensing steam in its own or working cylinder, and then made use of a separate vessel, now called the condenser.

The weight of steam is about 1800 times less than water.  I may here perhaps mention also that water will boil at 100 degrees Fahr. in vacuo, whereas in atmosphere it takes 212 degrees to boil.  There is also a thing perhaps worth knowing to all who wish to get the most stock out of bones, &c., that if they are boiled in a closed vessel, that is to say, under a pressure of steam, a very large increase in quantity of the stock will be produced, because the heat is increased.  A cubic inch of water, evaporated under ordinary atmospheric pressure, will be converted into a cubic foot of steam; and a cubic inch of water, evaporated as above, gives a mechanical force equal to raising about a ton a foot high.