(46.)

In 1762, Watt tried some experiments on the force of steam at a high pressure, confined in a close digester; and he then constructed a small model to show how motion could be obtained from that power. The practicability of what has since been called the High Pressure Engine, was demonstrated by him on this occasion; but he did not pursue the inquiry, on account of the supposed danger of working with such compressed steam as was required.

It is usual to provide, in the cabinets of experimental apparatus for the instruction of the students of universities, [Pg084] small working models of the most useful machines. In the collection for the illustration of the lectures delivered to the Natural Philosophy class in the University of Glasgow was a working model of Newcomen's atmospheric engine, applied to a pump for raising water; which, however, had never been found to work satisfactorily. The Professor of Experimental Philosophy of that day, Dr. John Anderson (the founder of the celebrated Andersonian Institution), sent this model in 1763 to Watt's workshop, to be repaired. Its defects soon disappeared, and it was made to work to the satisfaction of the professor and students.

This simple discharge of his duty, however, did not satisfy the artisan; and his wonted activity of mind rendered this model a subject of profound meditation, and led him into a course of practical inquiry respecting it, which formed the commencement of a most brilliant career of mechanical discovery. The improvement—we might almost say the creation—of the steam engine, by this great man, must not therefore be regarded, as so often happens with mechanical discoveries, as the result of fortuitous observation, or even of a felicitous momentary inspiration. Watt, on the other hand, conducted his investigation by a course of deep thought, and of experiments marked by the last refinement of delicacy and address. If he had received a more extended and liberal education, one would have thought that he had adopted for his guide the celebrated maxim of Bacon:—

"To write, speak, meditate, or act, when we are not provided with facts to direct our thoughts, is to navigate a coast full of dangers without a pilot, and to launch into the immensity of the ocean without either rudder or compass."

The model which he had repaired, had a cylinder of only two inches diameter, and six inches stroke. After he had put it in complete order, he found, that although the boiler was much larger in proportion to the cylinder than those of real engines, yet, that it was incapable of supplying the cylinder with steam in sufficient quantity to keep it at work. To enable it to continue to move, he found it necessary to lessen the quantity of water raised by its pump, so as to [Pg085] reduce the load on its piston very much below the proper standard according to the common rules for large engines.

He ascribed the great inferiority in the performance of the model, compared with the performance of the large engines, to the small size of the cylinder, and to its material. The cylinder of the model was brass, while those of large engines were of cast iron; and brass being a better conductor of heat than iron, he concluded that more heat in proportion was lost from this cause in the model, than in the larger engines. He observed that the small cylinder was so heated when the steam was admitted into it, that it could not be touched by the hand; but, nevertheless, that this heat contributed nothing to its performance, inasmuch as before the piston descended, the cylinder required to be cooled.