446 



THE STEAM-ENGINE. 



patent was taken out by them for the application of the crank to steam-engines. 

 This fact the said workman confessed, and the engineer who directed the works 

 acknowledged it ; but said, nevertheless, that the same idea had occurred to 

 him prior to his hearing of mine, and that he had even made a model of it be- 

 fore that time ; which might be a fact, as the application to a single crank was 

 sufficiently obvious. 



" In these circumstances, I thought it better to endeavor to accomplish the 

 same end by other means, than to enter into litigation ; and if successful, by 

 demolishing the patent, to lay the matter open to everybody. Accordingly, 

 in 1781, I invented and took out a patent for several methods of producing 

 rotative motions from reciprocating ones ; among which was the method of the 

 sun-and-planet wheels. This contrivance was applied to many engines, and 

 possesses the great advantage of giving a double velocity to the fly-wheel ; but 

 is perhaps more subject to wear, and to be broken under great strains, than a 

 simple crank, which is now more commonly used, although it requires a fly- 

 wheel of four times the weight, if fixed upon the first axis ; my application of 

 the double engine to these rotative machines rendered the counterweight un- 

 necessary, and produced a more regular motion." 



Watt's second patent here referred to, was dated 25th of October, 1781, and 

 was entitled, " A patent for certain new methods of applying the vibrating or 

 reciprocating motions of steam or fire engines to produce a continued rotative 

 or circular motion round an axis or centre, and thereby to give motion to the 

 wheels of mills and other machines." 



All the methods specified in this patent were intended to be worked by the 

 single-acting engine, already described, a counterweight being applied to impel 

 the machinery during the returning stroke of the engine, which weight would 

 be elevated during the descent of the piston. There were five different ex- 

 pedients proposed in the specification for producing a rotatory motion ; but, of 

 these five, two only were ever applied in practice. 



Suppose a rod or bar attached by a pin or joint at the upper extremity to the 

 working end of the beam of the engine, and by a similar pin or joint at the 

 lower extremity to an iron wheel fixed on the extremity of the axis of the fly- 

 wheel. One half of this wheel is formed of a solid semicircle of cast iron, 

 while the other half is constructed of open spokes, so as to be as light as is 

 consistent with strength. The position of the wheel on the axis is such that 

 during the returning stroke of the piston, when the operation of the steam is 

 suspended, the heavy semicircle of the wheel will be descending, and by its 

 weight will draw down the connecting bar, and thereby draw down the working 

 end of the beam, and draw up the piston in the cylinder. When the piston 

 descends and is driven by the power of the steam, the heavy semicircle of the 

 above-mentioned wheel will be drawn upward, and in the same way the motion 

 will be continued. 



The second method of producing a rotatory motion, which was subsequently 

 continued for many years in practical operation, was that which was called 

 the sun-and-planet wheels. A toothed wheel, A, fig. 13, called the sun- wheel, 

 was fixed on the axle of the fly-wheel, to which rotation was to be imparted. 

 The wheel B, called the planet-wheel, having an equal diameter, was fastened 

 on the end I of the connecting rod H I, so as to be incapable of revolving. 

 During the descent of the piston, the working end of the beam was drawn 

 upward, and the end I of the connecting rod travelled from C to D, through 

 the dotted semicircle C I D. The wheel B not being capable of revolving on 

 the centre I, would, during this motion, drive the sun-wheel A. During the 

 ascent of the steam-piston, the working end of the beam would descend, and 

 the centre I of the planet- wheel B. would be driven downward from D to C, 



