28 



Prof. A. Battelli and Mr. L. Maori on 



The results are recorded in the following table, where 

 they are arranged for increasing values of frequency and 

 of the number of turns of wire in unit of length of the 

 spiral. & 











Values of ^ 

 P 









No. of 





30 large 





. 





Spiral. 



turns per 





glass 











cm. 



Con- 



leyden-jars 



Air-con- 



2 air-con- 









tinuous 



and air- 



densers in 



densers in 



One small 







current. 



condensers 

 in parallel. 



parallel. 



series. 

 1-18 



condenser. 



Spiral a 



2*42 



1 



102 



1-14 



1-30 



» b 



3-82 



1 



1-17 



131 



1-34 



1-70 



o 



6 22 



1 



1-48 



166 



1-68 



1-89 



d 



7-52 



1 



1-56 



1-72 



203 



2-37 



From these results it may be seen that for every spiral 

 the resistance will always increase with increase of frequency 

 and also with diminution of distance of the spires. 



This phenomenon leads us to suppose that, while in a rec- 

 tilinear conductor the current will pass through a thin super- 

 ficial layer only, it becomes localized in a still more reduced 

 space when the same conductor is wound into a spiral; and 

 this may be expected, considering the mutual induction 

 effects between the various portions of the circuit. 



This localization is likely to affect the value of the self- 

 induction coefficient of the circuit, but it may be easily 

 understood — a fact borne out ;by the experiments we under- 

 took for this purpose — that this influence is quite insignificant 

 in comparison with the effect upon the resistance. 



26. From all the facts above mentioned it thus results that 

 the true value of the resistance of our spirals for a given period 

 will be obtained by multiplying the value for the resistance 

 R T , exhibited by the same wire when drawn out to a straight 



line, for the same period, by the ratio - n as found experi- 

 mentally in the above manner. P 



We thus have for our experiments the following values 

 for It/:— 



For the calorimeter No. 2 : 



*v= 



6-7 .10-6 



=0-983 xl-79 = l'7.6, 



