108 GOVERNORS. 



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 below the 

 centre of motion, which ensures a constant normal velocity. The break is: 

 in the first place, the variable friction between the combination 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 principle 

 for the chronograph and equatorial of Greenwich Observatory depend 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 pendulum 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 uniform 

 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. 



