"And whereas, in order to manufacture these engines with the necessary accuracy, and so that they may be sold at moderate prices, a considerable sum of money must be previously expended in erecting mills and other apparatus; and as several years and repeated proofs will be required before any considerable part of the public can be fully convinced of the utility of the invention, and of their interest to adopt the same, the whole term granted by the said letters patent may probably elapse before the said James Watt can receive an advantage adequate to his labour and invention:
"And whereas, by furnishing mechanical power at much less expense, and in more convenient forms, than has hitherto been done, his engines may be of great utility, in facilitating [Pg133] the operations in many great works and manufactures of this kingdom; yet it will not be in the power of the said James Watt to carry his invention into that complete execution which he wishes, and so as to render the same of the highest utility to the public of which it is capable, unless the term granted by the said letters patent be prolonged, and his property in the said invention secured for such time as may enable him to obtain an adequate recompense for his labour, time, and expense:
"To the end, therefore, that the said James Watt may be enabled and encouraged to prosecute and complete his said invention, so that the public may reap all the advantages to be derived therefrom in their fullest extent: it is enacted,
"That from and after the passing of this Act, the sole privilege and advantage of making, constructing, and selling the said engines hereinbefore particularly described, within the kingdom of Great Britain, and his majesty's colonies and plantations abroad, shall be, and are hereby declared to be, vested in the said James Watt, his executors, administrators, and assigns, for and during the term of twenty-five years," &c. &c.
(76.)
It is necessary to recollect, that notwithstanding the extensive and various application of steam power in the arts and manufactures, at the time to which our narrative has now reached, the steam engine had never been employed for any other purpose save that of raising water by working pumps. The motion, therefore, which was required was merely an upward force, such as was necessary to elevate the piston of a pump, loaded with the column of water which it raised. The following then is a description of the improved engine of Watt, by which such work was proposed to be performed:—
Fig. 21.
In the cylinder represented at C ([fig. 21.]), the piston P moves steam-tight. It is closed at the top, and the piston [Pg134] rod, being accurately turned, runs in a steam-tight collar, B, furnished with a stuffing-box, and is constantly lubricated with melted tallow. A funnel is screwed into the top of the cylinder, through which, by opening a stop-cock, melted [Pg135] tallow is permitted from time to time to fall upon the piston within the cylinder, so as to lubricate it, and keep it steam-tight. Two boxes, A A, called the upper and lower steam boxes, contain valves by which steam from the boiler may be admitted and withdrawn. These steam boxes are connected by a tube of communication T, and they communicate with the cylinder at the top and bottom by short tubes represented in the figure. The upper steam box A contains one valve, by which a communication with the boiler may be opened or closed at pleasure. The lower valve box contains two valves. The lower valve I communicates with the tube T′, leading to the condenser D, which being opened or closed, a communication is made or cut off at pleasure, between the cylinder C and the condenser D. A second valve, or upper valve H, which is represented closed in the figure, may be opened so as to make a free communication between the cylinder C and the tube T, and by that means between the cylinder C, below the piston and the space above the piston. The condenser D is submerged in a cistern of cold water. At the side there enters it a tube, E, governed by a cock, which being opened or closed to any required extent, a jet of cold water may be allowed to play in the condenser, and may be regulated or stopped, at pleasure. This jet, when playing, throws the water upwards in the condenser towards the mouth of the tube T′, as water issues from the rose of a watering pot. The tube S proceeds from the boiler, and terminates in the steam box A, so that the steam supplied from the boiler constantly fills that box. The valve G is governed by levers, whose pivots are attached to the framing of the engine, and is opened or closed at pleasure, by raising or lowering the lever G′. The valve G, when open, will therefore allow steam to pass from the boiler through the short tube to the top of the piston, and this steam will also fill the tube T. If the lower valve H be closed, its circulation beyond that point will be stopped; but if the valve H be open, the valve I being closed, then the steam will circulate equally in the cylinder, above and below the piston. If the valve I be open, then steam will rush through the tube T′ into the condenser; but this escape of the steam will be [Pg136] stopped, if the valve I be closed. The valve H is worked by the lever H′, and the valve I by the lever I′.