24 Prof. A. Battelli and Mr. L. Magri on 



In the case, however, of circuits wound into a spiral we 

 cannot say, a priori, that the same formulae will hold which 

 give the true resistance for rectilinear wires, and as a 

 theoretical investigation of this problem is wanting, we had 

 to undertake experimental researches in order to compare 

 the resistance presented by a spiral with the resistance opposed 

 to the same discharge by a wire drawn out into a straight 

 line. 



We determined the heat evolved in two successive parts of 

 the same circuit made up of two wires of the same diameter 

 and of the same substance — the one drawn out into a straight 

 line, the other wound into a spiral — first in the case of both 

 being traversed by a continuous current, next both being 

 traversed by an oscillatory discharge. 



For this purpose we used the calorimeters Nos. 1, 2, 3, 4, 5, 

 previously described. 



Let n and n' denote the displacements of the meniscus in 

 the capillary tubes of the spiral calorimeter and in the 

 rectilinear-wire calorimeter respectively, in the case of the 

 same continuous current traversing both of them ; let n T and 

 n- 1 denote the displacements produced in the same calori- 

 meters by the passage of a certain number of discharges. 



Accordingly, let Q, Q', Q 7 , Qr' denote the amounts of heat 

 evolved in the four cases above mentioned respectively. 



From the relations 



Q 



n 

 nS 



Q' 

 Qr' 





place 









nr 



n~r' 1 



n 



.Q' 



"Qr 



Q 

 Q" 



we have in the first place 



On the Other hand, denoting by I, I' the lengths of the 

 spiral wire and the rectilinear wire respectively, by R and R 

 their resistances, we have for the current with the period t 









Q 

 Q'~ 



1 



Qr 



Qr' 



R 



" R ; 



we 



may 



write 

















n? 



n 

 n' 



R 



: V 



