SECT. vin.J MANAGEMENT OF THE STEAM ENGINE. 263 



they receive the stroke ; and when they are bent beyond a certain degree they 

 cause a bell to ring, which gives the attendant notice that the engine requires 

 regulation. 



THE CONICAL PENDULUM OR GOVERNOR. 



550. If two or more balls be suspended from a revolving axis so as to revolve 

 with it, the balls will rise when the velocity is increased, and fall when it is dimi- 

 nished ; and by connecting awns to the rods by which the balls are suspended, 

 their rising or falling may be made to move a lever so as to open or close a valve, 

 or the like, on any change taking place in the velocity of the machinery ; and 

 hence it is employed to render an engine the regulator of its own power to the 

 effect it is to produce. 



In the construction of this apparatus it is necessary to consider the place of the 

 balls corresponding to the mean velocity, the range of motion, and the weight and 

 velocity of the balls. 



Different modes of combining the parts are used by different engineers ; one of 

 these is shown in Plate vm. Fig. 1. where g is the revolving axis, /the point of 

 suspension, jj the balls, e e the rods by which the balls are suspended. These rods 

 are connected to the rods i i, and by that means raise or depress the sliding piece 

 h, and with it the lever /, which acts on the throttle valve. The parts marked k k 

 are two rests to receive the balls when the engine is not in motion. 



551. The vertical distance between the point of suspension and the plane 

 in which the centres of the balls revolve, is the same as the length of a pendulum 

 which makes one vibration, forward and back again, in the same time the balls 

 make one revolution. The usual velocity for the axis is 30 revolutions per 

 second, and therefore the height should be the same as the length of the seconds' 

 pendulum, that is, 39'14 inches. To find the height for any other number of 

 revolutions per minute, divide 35226 by the square of the number; thus, for 

 twenty revolutions, 20 x 20 = 400, and 



= 88 '065 inches, the height required. 



552. The range may be settled from considering the greatest change of 

 velocity the machinery may acquire without injurious effect on the work ; and 

 with this range the governor ought to be capable of completely cutting off the 

 acting power. Now the greatest variation should not generally exceed one-tenth 

 of the velocity, that is, one-twentieth on either side of the mean ; and the range 

 of the plane of revolution will, in that case, be nearly one-fifth of the height of 



