Page:Popular Science Monthly Volume 12.djvu/149

Rh his first and his greatest invention—the separate condenser. His object in using it was, as he says himself, to keep the cylinder as hot as the steam that entered it. He was therefore the first to apprehend and to state a problem which the modern engineer is still vainly endeavoring completely to solve.

Watt was, at this time, twenty-nine years of age. Having taken this first step and made such a radical improvement, the success of the invention was no sooner determined than others followed in rapid succession as consequences of the exigencies arising from the first radical change in the old Newcomen engine.

But in the working out of the forms and proportions of details in the new engine, even Watt's powerful mind, with its stores of happily-combined scientific and practical information, was occupied for years. 35. In attaching the separate condenser, he first tried surface condensation, as in Fig. 14, which is a sketch of his first model; but this not succeeding well, he substituted the jet. Some provision became at once necessary for preventing the filling of the condenser with water.

Watt at first intended adopting the same expedient which worked satisfactorily with the less effective condensation of Newcomen's engine, i. e., leading a pipe from the condenser to a depth greater than the height of the column of water which could be counterbalanced by the pressure of the atmosphere; but he subsequently employed the air-pump, which relieves the condenser, not only of the water, but of the air which also usually collects in considerable volume, and vitiates the vacuum.

He next substituted oil and tallow for the water previously used in lubrication of the piston and keeping it steam-tight, in order to avoid the cooling of the cylinder incident to the use of water.

Still another cause of refrigeration of the cylinder, and consequent waste of power in its operation, was seen to be the entrance of the atmosphere, which came in at the top and followed the piston down the cylinder at each stroke.

This the inventor concluded to prevent by covering the top of the cylinder, and allowing the piston-rod to play through a "stuffing-box," which device had long been known to mechanics. He accordingly not only covered the top, but surrounded the whole cylinder with an external casing or "steam-jacket," and allowed the steam from the boiler to pass around the steam-cylinder and to press upon the upper