MB. C. W. SIEMENS ON UNIFOEM ROTATION. 



659 



is always obtainable), and the least motion in advance of the pendulum must automa- 

 tically reduce the source of power. This action would be effected instantly, notwith- 

 standing a considerable resistance in the valve, because the weight of the pendulum in 

 rotation represents, in this case, a store of power, inasmuch as its angular velocity would 

 have to be suddenly checked or increased as the case may be, unless the valve obeyed 

 the first appearance of a differential motion. In order to realize these conditions, it 

 was necessary to maintain the conical pendulum in question at a uniform angle of 

 rotation, notwithstanding the changes of driving- or sustaining-power which must neces- 

 sarily arise through its action upon the regulating valve of the engine ; and this could 

 only be accomplished by providing the means of destroying or absorbing any excess of 

 driving-power beyond what was necessary to overcome the friction of the instrument, 

 and which must tend otherwise to increase its angle of rotation. On the other hand, a 

 surplus of driving-power had to be provided to prevent an occasional collapse of the 

 pendulum in opening the valve. The sustaining- or driving-power of the pendulum was 

 obtained in taking advantage of the differential motion, a weight being attached to a 

 horizontal lever upon the throttle-valve spindle, which, in exerting a pressure of the 

 differential wheel against the two principal wheels, caused 

 an impulse to be given to the one connected with the pen- 

 dulum, whereas the third wheel was driven by the engine in 

 the direction proper to raise the weight continually. The 

 excess of driving-power imparted to the pendulum was 

 destroyed by calling into action a friction between two 

 solid substances at the moment when the angle of rotation 

 had reached its intended maximum ; or a liquid resistance 

 was introduced, such as a fan, rotating with the pendulum, 

 being dipped into a bath of mercury or other liquid, at the 

 moment when the extension of the pendulum was attained 

 (see fig. 2). 



The governors constructed on this principle are remark- 

 able for their instantaneous action upon the supply-valve 

 of the engine, when a sudden disturbance of the balance 

 between load and power takes place; and they possess 

 also, to the fullest extent, the power of maintaining the 

 regulated machine at the same speed, when the load 

 reaches its maximum, as when it is at its minimum. In 

 the hands of the Astronomer Eoyal the uniformity of 

 motion obtained by the use of this governor approaches 

 indeed that of an ordinary chronometer, yet it is not free 

 from objections resulting from the delicate adjustment and 

 frequent attention requisite to maintain it in good working 

 condition. In its application to the regulating of physical 



