1866.] Mi\ C,W. Siemens on Uniform Rotation, 71 



April 12, 1866. 

 Lieut-General SABINE, President, in the Chair. 



The following communications were read : — 



I. On Uniform Rotation." By C. W. Siemens, F.R.S. Received 



March 10, 1866. 



(Abstract.) 



The paper sets out with an inquiry into the conditions of the conical 

 pendulum as a means of obtaining uniform rotation. This instrument, as 

 applied by Watt to regulate the velocity of his steam-engines, is shown 

 to be defective, — first, because the regulated position of the valve depends 

 upon the angular position of the pendulums, and therefore upon the velocity 

 of rotation, which must be permanently changed in order to effect an ad- 

 justment of the valve; and secondly, because when the balance between force 

 and resistance of the engine at a given velocity is disturbed, the angular 

 position of the pendulums will not change until a power has been created 

 in them, through acceleration of the engine, sufficient to overcome the me- 

 chanical resistance of the valve, giving rise to a series of fluctuations before 

 a balance between the power and resistance of the engine is reestablished. 



These defects in Watt's centrifugal governor are shown to be obviated 

 in the chronometric governor, an instrument which was proposed by the 

 author of the paper twenty-three years ago, and which consists of a conical 

 pendulum proceeding at a uniform angle of rotation, and therefore at 

 uniform speed, which is made to act upon the regulating-valve by means 

 of a differential motion between itself and the engine to be regulated, which 

 latter has to accommodate itself to the rotations imposed by the indepen- 

 dent pendulum. The differential-motion wheels are taken advantage of 

 for imparting independent driving- or sustaining-power to the pendulum ; 

 and a constancy of the angle of rotation, notwithstanding unavoidable 

 fluctuations in the sustaining-power, is secured (within certain limits) by 

 caUing into play a break, or fluid resistance, at the moment when the angle 

 of rotation reaches a maximum, which maximum position is perpetuated by 

 increasing the sustaining-power beyond what is strictly necessary to over- 

 come the ordinary resistance of the pendulum. 



The chronometric governor is used by the Astronomer Royal to regulate 

 the motion of the large equatorial telescope and recording apparatus at 

 Greenwich, in which application a very high degree of regularity is at- 

 tained; but the instrument proved to be too delicate in its adjustments for 

 ordinary steam-engine use. 



After a short allusion to M. Foucault's governor, the paper enters upon 

 the description of a new apparatus which the writer has imagined for ob- 

 taining uniform rotation, notwithstanding great variations in the drivmg- 

 power, and which consists, in the main, of a parabolic cup, open at top and 



VOL. XV. H 



