ME. C. W. SIEMENS ON TJNIFOEM KOTATION. 663 



Automatic Dip of Cup. — We have assumed hitherto a rigid connexion between the 

 cup and its driving-spindle, and unless the cup does overflow, we are, indeed, justified in 

 this assumption, the spring E being too rigid to yield to the resistance of the cup in 

 motion when no work is performed. With an increase of power the resistance of the 

 cup also increases, and an ovei-flow of liquid proportionate to the power is produced ; 

 the connecting spring E must yield, at the same time, proportionately to the torsional 

 resistance thus created, and in the same ratio the cup will descend upon the helical 

 surface which serves for its guide. While, therefore, on the one hand, the h of our 

 formula increases with the overflow, it is diminished, in the same ratio, by the descent 

 of the cup, both depending directly upon the driving-power. When the stiffness and 

 length of the spring are so adjusted that the one action equals the other for any given 

 increase of power, it must equal it also for other amounts of increase within reasonable 

 limits, and strictly uniform rotation must be the result. The " reasonable limits " to this 

 automatic adjustment are imposed by the restricted orifice through which the liquid has 

 to penetrate into the cup, and also by the range of action of the spring, for which the 

 law of Mariotte is applicable. Experiments, to be hereafter described, have shown that 

 the driving-power may be varied between wide limits without producing any sensible 

 variation of speed. The final adjustment of the instrument to the normal velocity 

 required is moreover easily effected by raising or lowering the cup while it is running, 

 for which purpose the lower end of the upright spindle S is supported in the axis of an 

 adjusting screw E, as will be seen by inspection of Plate XXIX. fig. 1. 



Mange of power increased. — The range of power through which uniform rotation can 

 be obtained, may be further increased by an arrangement which is represented in Plate 

 XXIX. figs. 2 and 6, and which consists in arresting the liquid projected over the edge 

 of the cup by a belt of fixed vanes M, whence it drops through the zone of rotating radial 

 vanes L, which again impart tangential motion to it at the expense of the supei-fluous 

 driving-power of the cup of which they form part. It is hardly necessary to add that 

 these fixed and rotating vanes only increase the range of power of the instrument, without 

 in any way affecting its rate of rotation, and that a second set of fixed and rotating vanes 

 might be added with the same effect as the first. Although the rotating cup repre- 

 sented in Plate XXIX. figs. 2 and 6, is not provided with the automatic dip, it is equally 

 evident that the fixed and moveable vanes do not preclude that arrangement, which is 

 only dispensed with in such cases where great uniformity of motion is not required. 



An interesting application of such a " Liquid Gyrometer," as this instrument may 

 appropriately be called, would be that of obtaining synchronous motion at different 

 places connected by a telegraphic wire, for philosophical or telegraphic purposes ; but 

 in order to test its fitness for such purposes, I have constructed a clock of which it con- 

 stitutes the regulating principle, the moving power being obtained by electro-magnetism. 



Clock regulated by liquid in rotation.. — This clock is represented by Plate XXX. figs. 

 7 <& 8, and consists of three principal parts : — 



MDCCCLXVI. 4 Y 



