RELATION BETWEEN THE VARIATION OF RESISTANCE IN BISMUTH. 251 



Next it was filed down till a thickness 1 "56 mm. was obtained. The constants were now — 



c 1 = --42 c 2 = + 171. 



That is, the pure Hall effect has slightly increased ; the second effect has remained constant. 



From the above we conclude that when a plate is slit along the middle line, as Ia, the 

 transverse effect changes in numerical value, but not in sign ; the fact also that the effect 

 decreases, but qualitatively does not change as we pass from the middle towards the ends, 

 admits of a similar explanation. For, suppose we have a plate with electrodes (transverse) 

 at a and h (fig. 4), the rotatory effect may be represented as in the figure. When the 

 slits are made, several lines are interrupted (fig. 5) ; and when we approach the ends, the 

 complete number of lines is given only on one side of the connecting line. The single 

 safe conclusion to be drawn seems to be that the state of the plate, when it gives a 

 transverse effect, is symmetric with respect to the middle line of its length. 



The causes of the pure Hall effect and of the second effect seem to be very intimately 

 connected. Only by hammering or by filing a plate does it seem possible to vary one 

 without varying the other. 



Evidently the relations obtained between the transverse effect and the resistance 



variation for the various plates do not allow us to compare the values of the constants 



A fi 



in different plates, even when we use ; for this latter is a variable standard, depend- 



n 



ing on the plate and the temperature. 









