[From the Proceedings of the Royal Society, No. 100, 1868.] 



XXXIV. On Governors. 



A GOVERNOR is a part of a machine by means of which the velocity of 

 the machine is kept nearly uniform, notwithstanding variations in the driving- 

 power or the resistance. 



Most governors depend on the centrifugal force of a piece connected with 

 a shaft of the machine. When the velocity increases, this force increases, and 

 either increases the pressure of the piece against a surface or moves the piece, 

 and so acts on a break or a valve. 



In one class of regulators of machinery, which we may call moderators*, 

 the resistance is increased by a quantity depending on the velocity. Thus in 

 some pieces of clockwork the moderator consists of a conical pendulum revolving 

 within a circular case. When the velocity increases, the ball of the pendulum 

 presses against the inside of the case, and the friction checks the increase of 

 velocity. 



In Watt's governor for steam-engines the arms open outwards, and so 

 contract the aperture of the steam-valve. 



In a water-break invented by Professor J. Thomson, when the velocity is 

 increased, water is centrifugally pumped up, and overflows with a great velocity, 

 and the work is spent in lifting and communicating this velocity to the water. 



In all these contrivances an increase of driving-power produces an increase 

 of velocity, though a much smaller increase than would be produced without 

 the moderator. 



But if the part acted on by centrifugal force, instead of acting directly 

 on the machine, sets in motion a contrivance which continually increases the 



* See Mr C. W. Siemens "On Uniform Rotation," Phil. Trans. 1866, p. 657. 

 VOL. II. 14 



