1868.] Mr. J. C. Maxwell on Governors. 



273 



Governors have been constructed on this principle by Sir "W. Thomson 

 and hj M. Foucault. In the first, the force restraining the centrifugal piece 

 is that of a spring acting between a point of the centrifugal piece and a 

 fixed point at a considerable distance, and the break is a friction-break 

 worked by the reaction of the spring on the fixed point. 



In M. Foucault's arrangement, the force acting on the centrifugal piece 

 is the weight of the balls acting downward, and an upward force produced 

 by weights acting on a combination of levers and tending to raise the balls. 

 The resultant vertical force on the balls is proportional to their depth be- 

 low the centre of motion, which ensures a constant normal velocity. 

 The break is : — in the first place, the variable friction between the com- 

 bination of levers and the ring on the shaft on which the force is made 

 to act ; and, in the second place, a centrifugal air-fan through which 

 more or less air is allowed to pass, according to the position of the 

 levers. Both these causes tend to regulate the velocity according to the 

 same law. 



The governors designed by the Astronomer Royal on Mr. Siemens's prin- 

 ciple for the chronograph and equatorial of Greenwich Observatory de- 

 pend on nearly similar conditions. The centrifugal piece is here a long 

 conical pendulum, not far removed from the vertical, and it is prevented 

 from deviating much from a fixed angle by the driving-force being rendered 

 nearly constant by means of a differential system. The break of the pen- 

 dulum consists of a fan which dips into a liquid more or less, according to 

 the angle of the pendulum with the vertical. The break of the principal 

 shaft is worked by the differential apparatus ; and the smoothness of motion 

 of the principal shaft is ensured by connecting it with a fly-wheel. 



In the third kind of governor a liquid is pumped up and thrown out over 

 the sides of a revolving cup. In the governor on this principle, described by 

 Mr. C. W. Siemens, the cup is connected with its axis by a screw and a 

 spring, in such a way that if the axis gets ahead of the cup the cup is 

 lowered and more liquid is pumped up. If this adjustment can be made 

 perfect, the normal velocity of the cup will remain the same through a 

 considerable range of driving-power. 



It appears from the investigations that the oscillations in the motion 

 must be checked by some force resisting the motion of oscillation. This 

 may be done in some cases by connecting the oscillating body with a body 

 hanging in a viscous liquid, so that the oscillations cause the body to rise 

 and fall in the liquid. 



To check the variations of motion in a revolving shaft, a vessel filled with 

 viscous liquid may be attached to the shaft. It will have no effect on uni- 

 form rotation, but will check periodic alterations of speed. 



Similar effects are produced by the viscosity of the lubricating matter 

 in the sliding parts of the machine, and by other unavoidable resistances ; 

 so that it is not always necessary to introduce special contrivances to check 

 oscillations. 



