194 Mr. H. Pender on the Magnetic 



M 3 , motor driving commutator. 



V, Yoss machine. 



L, leyden-jars. 



C, commutator. 



S, a high potential reversing switch. 



K, key in galvanometer circuit. 



T, resistance-boxes and cell forming test circuit. 



G, galvanometer. 



s, scale of same. 



X, counter shaft. 



The advantage of this galvanometer method of detecting 

 the existence of the magnetic action of electrical convection 

 over the magnetometer methods, is clearly seen in this possible 

 arrangement. Instead of having the delicate magnetic 

 detector which must be employed, up close to the rotating 

 disks, where it is subject to all kinds of disturbing elements, 

 as is necessary when a magnetometer is used, it can in this 

 method be placed as far as one may desire from all the rest 

 of the apparatus. The three motors M, M 2 M 8 were so placed 

 as to reduce their action on the coil and galvanometer to a 

 minimum. When placed as shown, there was no appreciable 

 action on the coil ; but on turning the current on the large 

 motor M 2 , the zero of the galvanometer was changed about 

 15 mm. As the speed of the motor was kept constant, how- 

 ever, during a series of observations, this was a perfectly 

 steady deflexion, and consequently of no particular dis- 

 advantage. The disks were set up at right angles to the 

 meridian, for convenience in placing the rest of the apparatus. 

 There was no appreciable effect due to tbeir thus cutting the 

 lines of force of the earth's field ; i. e., there was no effect on 

 running the apparatus with the disks uncharged. 



In the figure all connexions are omitted for the sake of 

 clearness. These, however, can be readily described in con- 

 nexion with the various figures. 



Galvanometer Circuit. — This circuit was completely in- 

 closed in a continuous metal shield throughout its entire 

 extent. This shield was connected to earth. The lead wires 

 from the galvanometer lead first to a specially constructed 

 mercury- switch K, inclosed in a wooden box, lined with tin- 

 foil — the switch was thus protected both from thermal and 

 from electrostatic effects. One of the leads was connected 

 to the earth. From the switch ran two lead wires to the 

 springs of the commutator. The rods of the commutator 

 were connected to the terminals of the coil. 



Charging Connexions. — All high potential wires were sus- 



