In the meantime, Watt had associated himself with a business partner named Boulton, under the firm name of Boulton and Watt. In 1776 a special act of legislation extending the term of Watt's original patent for a period of twenty-five years had been secured. All infringements were vigorously prosecuted, and the inventor, it is gratifying to reflect, shared fully in the monetary proceeds that accrued from his invention.
WATT'S ROTATIVE ENGINE.
The lower figure shows the earliest type of mechanism through which Watt applied his engine to other uses than that of pumping. The so-called sun-and-planet gearing, through which rotary motion was attained, is seen at the lower right-hand corner of the figure. The upper figure shows a later and much improved type of the Watt engine, in which the sun-and-planet gearing has been supplanted by a simple crank.
Notwithstanding the early recognition of the possibility of securing rotary motion with Watt's perfected Newcomen engine, it was long before the full possibilities of the application of this principle were realized, even by the most practical of machinists. Watt himself apparently appreciated the possibilities no more fully than the others, as the use of his famous engines "Beelzebub" and "Old Bess" in the establishment of Boulton and Watt amply testifies. It appears that Boulton had been an extensive manufacturer of ornamental metal articles. To drive his machinery at Soho he employed two large water wheels, twenty-four feet in diameter and six feet wide. These sufficed for his purpose under ordinary conditions, but in dry weather from six to ten horses were required to aid in driving the machinery. When Watt's perfected engine was available, however, this was utilized to pump water from the tail race back to the head race, that it might be used over and over. "Old Bess" had a cylinder thirty-three inches in diameter with seven-foot stroke, operating a pump twenty-four inches in diameter; it therefore had remarkable efficiency as a pumping apparatus. But of course it utilized, at best, only a portion of the working energy contained in the steam; and the water wheels in turn could utilize not more than fifty per cent. of the store of energy which the pump transferred to the water in raising it. Therefore, such use of the steam engine involved a most wasteful expenditure of energy.
It was long, however, before the practical machinists could be made to believe that the securing of direct rotary power from the piston could be satisfactorily accomplished. It was only after the introduction of higher speed and heavier fly-wheels, together with improved governors, that the speed of rotation was so equalized as to meet satisfactorily the requirements of the practical engineer, and ultimately to displace the wasteful method of securing rotary motion indirectly through the aid of pump and water wheel. It may be added, that the centrifugal governor, with which modern engines are provided to regulate their speed, was the invention of Watt himself.
FINAL IMPROVEMENTS AND MISSED OPPORTUNITIES
In the year 1782 Watt took out patents which contained specifications for the two additional improvements that constituted his final contribution to the production of the steam engine. The first of these provided for the connection of the cylinder chamber on each side of the piston with the condenser, so that the engine became double acting. The second introduced the very important principle,—from the standpoint of economy in the use of steam—of shutting off the supply of steam from the cylinder while the piston has only partially traversed its thrust, and allowing the remainder of the thrust to be accomplished through the expansion of the steam. The application of the first of these principles obviously adds greatly to the efficiency of the engine, and in practise it was found that the application of the second principle produces a very great saving in steam, and thus adds materially to the economical working of the engine.