WILL/AM SIEMENS, F.R.S. 



119 



that the compensation is effected, under all circumstances, by one 

 or two turns of the regulating screw supporting the vertical spindle. 



\Ylien the regulation of the cup is once effected, it continues to 

 rotate at a remarkably uniform rate. Change of temperature 

 affects the density of the liquid considerably, but does not in- 

 fluence the rate of the cup otherwise than inasmuch as it affects 

 the level in the cup-chamber, which will rise with increase of 

 temperature proportionately to the depth of liquid it contains, and 

 which is inconsiderable. The lineal dimensions of the cup, and 

 the length of the suspending spring, will also increase, all tending 

 to lower the rate with increase of temperature ; but, on the 

 other hand, the length of the upright cup-spindle increases with 

 increase of temperature, and in regulating the length and com- 

 position of that spindle properly, entire compensation for change 

 of temperature is effected. The cup-chamber being entirely closed 

 against the atmosphere, no fault can arise through evaporation or 

 dispersion of the liquid within moderate periods of time. 



In the case of the clock under consideration, no compensation 

 for change of temperature was provided, nor is the cup entirely 

 balanced by the spring, yet its rate is as uniform as that of the 

 common clock with which it has been compared ; but in order to 

 test the regulating-power of the instrument, the driving-power 

 was varied by the introduction of artificial resistances into the 

 galvanic circuit, when the following results were observed : 



