WILLIAM SIEHfENS, F.R.S. 109 



in Watt's centrifugal governor, I proposed, twenty-three years 

 ago, in connexion with my brother, Werner Siemens, a governor 

 based also on the conical pendulum, which in this case was to be 

 independent in its action of change in its angular rotation, and, 

 moreover, was to be provided always with a store of power ready 

 to overcome the resistance of the valve at the first moment when 

 the balance between the power and load of the engine was dis- 

 turbed. This instrument (the chronometric governor) has been 

 applied with success in many cases where engines were required to 

 work with great regularity under varying conditions of load ; it 

 has also received an interesting application by the Astronomer 

 Royal for regulating astronomical and chronographical instru- 

 ments, proving the high degree of precision of which it is capable. 

 The leading idea involved in this governor consisted in providing 

 a conical pendulum in uniform rotation, and in establishing a 

 differential motion between it and the wheel driven by the engine, 

 which differential motion was made to act upon the source of 

 power of the latter. If this idea could be carried out, it was 

 evident that the engine, or machine to be governed, must suit its 

 motion closely to that of the independent rotating pendulum, 

 because the least retardation on its part must immediately result 

 in an enlargement of the valve-orifice (it being understood that an 

 increase of available power is always obtainable), and the least 

 motion in advance of the pendulum must automatically 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 

 to 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 necessarily 

 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 



