244 Mr. Albert Griffiths : Some 



VII. Let ^=210°. Reading=491. 



VIII. Let pt = 240°. Reading = 505. 



IX. Let ^=270°. Reading = 512. 



X. Let ^=310°. Reading=519. 



XL Let ^=330°. Reading =532. 



The theoretical results indicate a sudden change at 0°, 

 involving an impossibility of reading for small values of pt 

 ( r must lie between + 1 and 0) ; later a gradual rise in 

 reading to 180°, again a sudden change, and a repetition of 

 the preceding. 



The measurements of the angles of lead are confessedly 

 rough (they were made with the unassisted eye), theory 

 would indicate an addition of 5° to each reading. I en- 

 deavoured to make more observations, but owing to difficulties 

 decided to leave more accurate determinations to a future 

 time. 



Theory indicates that difficulties might be expected at the 

 position with which I always started, viz., a lead of about zero. 



I may mention that the telephones I employed were not 

 nearly so useful with currents of low frequency as with 

 higher. In fact a current from the alternator, which was none 

 too powerful for use with the telephones and bridge, heated 

 the bismuth spiral so as to perceptibly alter its resistance. I 

 found that in a strong field the resistance of bismuth, as 

 measured by a telephone, diminishes with increase of tempera- 

 ture : the same is true with a constant current, as, I found 

 out after making my own experiments in May, was noticed 

 by Van Aubel* a year or more ago, and later (with more 

 detail) by Henderson f. 



That the resistance of bismuth in a strong field should 

 diminish with increase in temperature is what one would expect 

 if, as surmised, the increase of resistance is due to changes con- 

 nected with the diamagnetism of bismuth. I do not know 

 of any researches, but it is probable that the susceptibility of 

 bismuth will diminish (numerically) with increase of tempera- 

 ture : assuming this, we should expect that the effect of an 

 increase in temperature will be complex in character — that, so 

 far as the effect of the demagnetization due to rise in tempera- 

 ture is concerned, the resistance will diminish; that, so far as 

 the ordinary action of heat is concerned, the resistance will 



* Journal de Physique, September 1893, p. 108. 

 t Phil. Mag. November 1894. 



