o~2 Trof. E. Wiedemann on the Behaviour of Gases 



the negative discharge is nearly the same, in spite of the 

 difference in the number of the discharges. 



At a pressure of 0*7 millim., for example, the proportion of 

 the number of positive discharges to that of the negative 

 discharges is about as 1 : 4, the quantities of heat produced are 

 about 0-40 and 0*43. 



With decreasing pressure the heating diminishes rapidly, 

 without p )ass ^ n 9 through a minimum corresponding to the 

 maximum number of discharges. A slight increase, however, 

 was observed in some of the other tubes. 



A special series of experiments had for their object to decide 

 whether the heating in a capillary tube is dependent on the 

 form of the electrodes or not. The arrangement of fig. 9 was 

 employed. The measurements were made at several pressures, 

 and with either positive or negative electrode put to earth, 

 but without any spark included. The conducting-wires from 

 the machine were plunged in c or d, the wires leading to the 

 galvanometer in a or b. 



The following table gives the amounts of heat produced : — 



p 



Spheres. 



Points. 



+ 



- 



+ 



- 



9-7 

 35 

 04 



X 



2-2 

 1-18 

 042 

 0-50 



2-4 



0-45 

 0-24 



2-2 

 1-17 

 0-44 

 0-33 



2-2 



0-44 

 0-24 



The amounts of heat, then, are in general nearly independent 

 of the form of the electrodes. 



This result agrees with ihat found when sparks are 

 included. 



Moreover the number of discharges alters very little with 

 the form of the electrodes. Since somewhat long and wide 

 portions of tube intervened between the electrodes and the 

 capillary tube, the discharges were somewhat irregular, as 

 they usually are in similar cases. 



G. Wiedemann * has shown by experiments with Holtz's 

 machine that the quantities of heat produced in a wide tube 

 and in a narrow tube per unit length are always equal — a result 

 which has since been confirmed by Naccari and Bellati f by 

 use of the induction-coil. 



I have, in the next place, made a further series of experi- 

 ments with different thick-walled capillary tubes. 



* Wiedemann, Pogg. Ann. clviii. p. 35, 187G 

 + Naccari and Bellati, Atti deW 



p. 720. 



1st. Ven. (o), vi. 1878 ; Beibl. ii. 



