Il6 THE SCIENTIFIC PAPERS OF 



1. The pedestal containing a battery of two " Marie Davy's 

 elements " suitably arranged. 



2. The body of the clock, with sides formed of plate glass, con- 

 taining an electro-magnet, by which rotatory motion is imparted to 

 an iron bar or keeper fixed upon the vertical main axis which 

 passes into 



3. the regulating chamber, consisting of a close cylindrical glass 

 vessel with domed glass top containing the rotating cup and a 

 certain quantity of paraffin oil, which fluid is particularly appli- 

 cable on account of its perfect fluidity and non-affinity for the 

 materials composing the regulator. 



The regulating cup is in this instance formed of vulcanite, and 

 is suspended from the top of the vertical axis by means of a spiral 

 spring, which, being fixed at both ends, not only supports the 

 weight of the cup but acts also as a torsional spring, enabling the 

 cup to descend upon its helical central guide whenever an increase 

 of driving-power calls into existence its equivalent of torsional 

 resistance. 



The rings of stationary and rotating vanes are dispensed with in 

 this instance, because no great variations in the driving-power are 

 contemplated. The electro-magnet acts by attraction of the 

 armature during a small portion of its rotation, and one contact 

 only is required, which is so arranged that no destruction of the 

 metallic surfaces can arise through the discharge of extra-current 

 sparks, which latter are received by an elastic point of platinum 

 slightly in advance of the proper contact surface and moved by 

 the same eccentric. By this simple arrangement the usual diffi- 

 culty attending dry contacts is avoided, and a continued action of 

 the instrument ensured. A train of reducing-wheels communi- 

 cates the motion of the cup-spindle to hands upon the face of the 

 clock, which record hours and minutes in the usual manner. 



The diameter of the rotating cup being = 0'040 metre, and the 

 height of its edge over the surface of the liquid = 0-034 metre, the 

 number n of its rotations per second in accordance with our 

 formula 



metre x -038 metre =6 . 9 reyolutions gecon(L 



Experiment gave, on the contrary, a speed of 7*5 revolutions 



