Experiments ivitfi Alternating Currents. 215 



increase. In general we might expect a temperature to be 

 soon reached at which the latter action is greater than the 

 former. 



I should expect the curves which give the relation between 

 temperature and resistance, in the case of a steady current, to 

 be somewhat (to express myself loosely) asymptotic, the 

 asymptote being the line which gives the relation between 

 the temperature and resistance when the bismuth is in zero 

 field. 



In addition, taking my theory — which may be applied to 

 currents of the frequencies under consideration or to those of 

 10,000 per second as imagined, perhaps correctly, by Lenard — 

 as a working hypothesis, I have formed the expectation that 

 the difference between the resistances as measured by tele- 

 phone and galvanometer would diminish with increase of 

 temperature ; this is perhaps worthy of investigation. 



There is another action which may exist, — perhaps also 

 worthy of research ; I have not had the advantage of study- 

 ing the original paper, but Geronza and Finzi * find that an 

 alternating current influences the susceptibility of iron, nickel, 

 and steel ; possibly the susceptibility of bismuth may be 

 influenced in like manner, and indirectly affect the resistance. 



I hope at some future time to carry on some experiments 

 with alternating currents perfectly harmonic in character, 

 a telephone responding only to the frequency under considera- 

 tion, and to endeavour to determine what is the lowest 

 frequency at which a change in resistance is perceptible ; 

 also to examine whether the shape of the section of the bismuth 

 wire is of any importance. 



Summary. 



The paper contains a few new experiments dealing with 

 the action of alternating currents when sent through the coils 

 of a galvanometer. 



A convenient and satisfactory arrangement is described for 

 diminishing the spark on breaking a galvanic circuit. 



A description is given of experiments, made with the 

 bismuth spiral, all of which (and others of which no descrip- 

 tion is given) gave negative results. 



A theory is elaborated which explains, to a limited extent, 

 the fact that in a strong field the resistance of bismuth is 

 greater when measured with an alternating than with a 

 constant current. 



* Beiblatter, vol. xviii. No. 3, p. 375. 

 Phil Mag. S. 5. Vol. 39. No. 238. March 1895. S 



