Stories of Invention, Told by Inventors and their Friends

by Edward Everett Hale

When Watt found that water in its conversion into vapor became such a reservoir of heat, he was more than ever bent on economizing it; for the great waste of heat involving so heavy a consumption of fuel was felt to be the principal obstacle to the extended employment of steam as a motive power. He accordingly endeavored, with the same quantity of fuel, at once to increase the production of steam and to diminish its waste. He increased the heating surface of the boiler by making flues through it; he even made his boiler of wood, as being a worse conductor of heat than the brickwork which surrounds common furnaces; and he cased the cylinders and all the conducting pipes in materials which conducted heat very slowly. But none of these contrivances were effectual; for it turned out that the chief expenditure of steam, and consequently of fuel, in the Newcomen engine, was occasioned by the reheating of the cylinder after the steam had been condensed, and the cylinder was consequently cooled by the injection into it of the cold water. Nearly four fifths of the whole steam employed was condensed on its first admission, before the surplus could act upon the piston. Watt therefore came to the conclusion that to make a perfect steam-engine it was necessary that the cylinder should be always as hot as the steam that entered it; but it was equally necessary that the steam should be condensed when the piston descended, nay, that it should be cooled down below 100°, or a considerable amount of vapor would be given off, which would resist the descent of the piston, and diminish the power of the engine. Thus the cylinder was never to be at a less temperature than 212°, and yet at each descent of the piston it was to be less than 100°,—conditions which, on the very face of them, seemed to be wholly incompatible.

Though still occupied with his inquiries and experiments as to steam, Watt did not neglect his proper business, but was constantly on the look-out for improvements in instrument-making. A machine which he invented for drawing in perspective proved a success; and he made a considerable number of them to order, for customers in London as well as abroad. He was also an indefatigable reader, and continued to extend his knowledge of chemistry and mechanics by perusal of the best books on these sciences.

Above all subjects, however, the improvement of the steam-engine continued to keep the fastest hold upon his mind. He still brooded over his experiments with the Newcomen model, but did not seem to make much way in introducing any practical improvement in its mode of working. His friend Robison says he struggled long to condense with sufficient rapidity without injection, trying one experiment after another, finding out what would not do, and exhibiting many beautiful specimens of ingenuity and fertility of resource. He continued, to use his own words, "to grope in the dark, misled by many an ignis fatuus." It was a favorite saying of his that "Nature has a weak side, if we can only find it out;" and he went on groping and feeling for it, but as yet in vain. At length light burst upon him, and all at once the problem over which he had been brooding was solved.

THE SEPARATE CONDENSER.

One Sunday afternoon, in the spring of 1765, he went to take an afternoon walk on the Green, then a quiet grassy meadow used as a bleaching and grazing ground. On week days the Glasgow lasses came thither with their largest kail-pots to boil their clothes in; and sturdy queans might be seen, with coats kilted, trampling blankets in their tubs. On Sundays the place was comparatively deserted; and hence Watt, who lived close at hand, went there to take a quiet afternoon stroll. His thoughts were as usual running on the subject of his unsatisfactory experiments with the Newcomen engine, when the first idea of the separate condenser suddenly flashed upon his mind. But the notable discovery is best told in his own words, as related to Mr. Robert Hart, many years after:—

"I had gone to take a walk on a fine Sabbath afternoon. I had entered the Green by the gate at the foot of Charlotte Street, and had passed the old washing-house. I was thinking upon the engine at the time, and had gone as far as the herd's house, when the idea came into my mind that as the steam was an elastic body, it would rush into a vacuum, and if a communication were made between the cylinder and an exhausted vessel, it would rush into it and might be then condensed without cooling the cylinder. I then saw that I must get rid of the condensed steam and the injection water if I used a jet, as in Newcomen's engine. Two ways of doing this occurred to me. First, the water might be run off by a descending pipe, if an off-let could be got at the depth of 35 or 36 feet, and any air might be extracted by a small pump. The second was to make the pump large enough to extract both water and air." He continued: "I had not walked farther than the Golf-house when the whole thing was arranged in my mind."

Great and prolific ideas are almost always simple. What seems impossible at the outset appears so obvious when it is effected, that we are prone to marvel that it did not force itself at once upon the mind. Late in life Watt, with his accustomed modesty, declared his belief that if he had excelled, it had been by chance, and the neglect of others. To Professor Jardine he said that when it was analyzed the invention would not appear so great as it seemed to be. "In the state," said he, "in which I found the steam-engine, it was no great effort of mind to observe that the quantity of fuel necessary to make it work would forever prevent its extensive utility. The next step in my progress was equally easy,—to inquire what was the cause of the great consumption of fuel: this, too, was readily suggested, viz., the waste of fuel which was necessary to bring the whole cylinder, piston, and adjacent parts from the coldness of water to the heat of steam, no fewer than from fifteen to twenty times in a minute." The question then occurred, How was this to be avoided or remedied? It was at this stage that the idea of carrying on the condensation in a separate vessel flashed upon his mind, and solved the difficulty.

Mankind has been more just to Watt than he was to himself. There was no accident in the discovery. It had been the result of close and continuous study; and the idea of the separate condenser was merely the last step of a long journey, a step which could not have been taken unless the road which led to it had been traversed. Dr. Black says, "This capital improvement flashed upon his mind at once, and filled him with rapture,"—a statement which, in spite of the unimpassioned nature of Watt, we can readily believe.

On the morning following his Sunday afternoon's walk on Glasgow Green, Watt was up betimes, making arrangements for a speedy trial of his new plan. He borrowed from a college friend a large brass syringe, an inch and a third in diameter, and ten inches long, of the kind used by anatomists for injecting arteries with wax previous to dissection. The body of the syringe served for a cylinder, the piston-rod passing through a collar of leather in its cover. A pipe connected with the boiler was inserted at both ends for the admission of steam, and at the upper end was another pipe to convey the steam to the condenser. The axis of the stem of the piston was drilled with a hole, fitted with a valve at its lower end, to permit the water produced by the condensed steam on first filling the cylinder to escape. The first condenser made use of was an improvised cistern of tinned plate, provided with a pump to get rid of the water formed by the condensation of the steam, both the condensing-pipes and the air-pump being placed in a reservoir of cold water.