20 



Pro f . A. Battelli and Mr. L. Ma cm 



Fi°\ 5. 



offered by the metallic parts to the oscillatory discharge was 

 indispensable to us as an element of comparison, in order to 

 derive from it the effective resistance of the spark. 



This comparison was made by measuring the amount 

 of heat evolved by the same discharge either in the single 

 metallic portions of the circuit or in the spark, and for this 

 purpose we made use of special calorimeters. 



(3. Calorimeters. 



20. Calorimeters for metallic circuit. — Those adopted by 

 us for measuring the energy evolved in the 

 metallic portions of the circuit had the form 

 shown in tig. 5. 



The rectilinear wire or the spiral through 

 which the condenser was discharged, termi- 

 nated in two short platinum wires fused to 

 both ends of a glass tube. To this tube 

 there was connected in a A~ertical position 

 the uniform capillary tube C, conveniently 

 divided and soldered by its lower part to a 

 wider tube, to which the cock R was con- 

 nected, the latter being, by means of a 

 rubber tube, put into connexion with the 

 small mercury reservoir M. The whole of 

 the tube T, the interior of the tube on 

 which the spiral was wound, and part of 

 the capillary tube C were filled up with 

 toluol. 



The mercury reached at least one centi- 

 metre above the cock R, allowing thus ol 

 the height of toluol in the capillary tube C 

 being regulated, and preventing its leaving 

 by the cock R. Round the calorimeter thus 

 formed a glass jacket was placed, in order 

 to regularize the interchange of heat with 

 the atmosphere. 



21. Calorimeter for spark. — This was 

 made up of two ovoidal recipients RR' (fig. fi), 

 one of which was interior to the other, the in- 

 terval being filled up with toluol occupying 

 also the capillary tube T. 



The latter was, on the other hand, connected to a reservoir 

 P containing mercury by a tube furnished with a cock 

 and a rubber tube. By raising or lowering P, the height 

 of mercury in the tube, and thus that of the toluol in 

 the tube T could be varied. 



QAR 



