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



© 



He determined with a sort o£ liquid ther mo-rheostat the 

 heat evolved in the circuit, and having also measured in 



2 2 



the form ^° ^ (where q is the initial quantity of 



electricity, g 1 the residual electricity, and C the capacity of 

 the condenser) the total work of discharge, he could deduce 

 by difference the work spent in the spark. 



The main action of the spark would consist, according to 

 Heydweiller, not in its resistance, but in the work necessary 

 to maintain the discharge-potential. 



Cardani *, in investigating the resistance of the spark, 

 dealt indirectly with the distribution of energy in a circuit 

 of constant and small self-induction, where by varying the 

 capacity of the condenser the period of oscillation was also 

 altered between certain limits. Studying next the discharge 

 in rarefied gases, Cardani observed that the part of the energy 

 dissipated in the spark depends on the form of the discharge 

 and on the section of the spark itself, being much larger when 

 the discharge passes in the form of a luminous brush. 



But both Heydweiller's and Cardani's measurements fail 

 to afford the complete solution of this part of the problem, as 

 those of Heydweiller apply only to continuous discharges, while 

 those of Cardani are not relative to the energy disposable. 



For the solution of the problem it is necessary that the 

 determinations of the thermal energy evolved in the different 

 parts of the circuit should be executed simultaneously; as it is 

 important also that in measurements of this kind the sum 

 of such energies should be compared with the total energy 

 disposable in the discharge. 



As, moreover, the arrangement of our experiments for the 

 determination of the period of oscillation and for measuring 

 the various resistances was such as to allow of the necessary 

 measurements being made simultaneously, we also tried to 

 draw some conclusions relative to the energy found in the 

 different parts of the discharge-circuit, as compared with the 

 total disposable energy. 



On this account, in addition to the above-described deter- 

 minations of the capacity and the heat evolved in the metallic 

 parts and in the spark, we had to ascertain the discharge- 

 potential and the value of the residual charge. 



Electrometer. 

 39. In order to obtain the value of the potential at which 

 the discharge began, we availed ourselves of a Kighi f idio- 



* Nuovo Cimento [3] xxxv. p. 142 (1894) ; [4] xi. p. 113 (1900). 

 t Nuovo Cimento [2] xvi. p. 89 (1876). 



