rli Rcn/al Astronomical Society. 



*^^he first is, the amount of friction in the rotation of the balls, 

 •which, indeed, is so great, that in the clock-work used for equatoreal 

 motion it consumes by far the greater part of the power. In the 

 shape in which Sieman's regulator is usually applied to steam-engines, 

 with one ball revolving by a rod whose support is a ball-and-socket 

 joint, the friction is intolerably great. When balls are mounted on 

 a vertical spindle, the friction, although much diminished, is still far 

 too great. The Astronomer Royal had therefore directed his 

 thoughts to the mounting of the conical pendulum, so as greatly to 

 diminish the friction. In the summer of 1846 he chanced to see at 

 the Gewerbe Aufstellung of Wiesbaden* a beautiful centrifugal-ball 

 clock, intended for a drawing-room. The maker had acutely re- 

 marked that the circular motion might be resolved into two rectan- 

 gular motions, and that each of these might be produced by the vi- 

 bratory motion of a knife-edge. The pendulum, therefore, vibrated 

 immediately by a knife-edge upon concave agates carried by a small 

 frame, and this frame itself was furnished with knife-edges in the 

 direction transversal to the former, which vibrated upon concave 

 agates carried by the fixed frame of the clock. The pendulum thus 

 moved with so much freedom that it was kept in conical vibration 

 by a small maintaining power, acting ultimately by a light radial arm 

 to maintain the rotation. The arc of expansion was determined (as 

 in ordinary pendulums) merely by the resistance of the air. 



This motion on knife-edges is liable to the same objections as the 

 use of knife-edges for clock- pendulums. The Astronomer Royal 

 therefore proposes to substitute for them a mounting by springs. 

 The pendulum is immediately supported by two springs from a frame, 

 and this frame is itself supported from the fixed parts of the clock- 

 frame by two springs whose relative position is transversal to that 

 of the former, and whose plane of vibration is transversal to that of 

 the former ; the form of the intermediate frame being such that, when 

 the pendulum hangs in a vertical position, the upper ends of the 

 four springs will be in one horizontal plane, and the lower ends 

 will also be in one horizontal plane. A model of this mounting was 

 exhibited. The motion is most satisfactory ; the pendulum revolves 

 many times before the diameter of its circle is diminished to one-half. 

 In the complete clock-work the power of the train is to act on this 

 by a radial arm. 



The second defect, which will only be sensible when the mecha- 

 nism has received these improvements (but of the distinct effect of 

 which the Astronomer Royal has no doubt), is the want of compen- 

 sation for the thermal expansion of the pendulum rod. Supposing 

 the limiting arc of vibration determined by rotation within a ring, 



* The mechanical talent of inland Germany, having had little employ- 

 ment in the construction of powerful engines or manufacturing machinery, 

 appears to have developed itself in the invention of clock-work. The 

 Museum in the Schioss of Gotha contains a remarkable collection of 

 clocks embodying every conceivable device. None, however, has appeared 

 to the Astronomer Royal so remarkable for the accuracy of its mechanical 

 conception as that which is described in the text. 



