226 



Messrs. AV. Macnab and E. Pdston. 



A A is the datum line; the point of departure a of the spot of 

 light from it shows when the first charge was fired ; the spot of light, 

 owing to the deflection of the galvanometer, travelled rapidly to the 



Fig. 3. 



left, imtil the maximum point Pi was reached, then more slowly- 

 returned, as cooling set in, towards its normal position, h, c, Po, P3, 

 are the corresponding points in the other two experiments. 



The maximum deflections, as shown by Pi, Po, P3, are seen to be 

 in inverse order to the thickness of the couples used, the greatest 

 deflection being obtained with the thinnest couple. 



