Luminosity of Gases through Electrical Discharges. 249 



The inductorium was excited by two Bunsen elements. The 

 calorimetric determinations were carried out in the following 

 manner: — First, for 5-10 minutes before the experiment the 

 course of the thermometer was observed ; then, exactly at the 

 minute, the primary circuit of the inductorium was closed. 

 When with the play of the interruptor a sufficient augmentation 

 of the temperature of the calorimeter had taken place, the cur- 

 rent-circuit was again opened, at a moment which was read off, 

 and the course of the thermometer followed again during 

 5-10 minutes. From the rise of temperature which had 

 taken place, corrected in the well-known manner, and from 

 the number of the discharges, counted on the strip of paper 

 of the marker, the quantity of heat generated at each single 

 discharge in the capillary tube could be calculated. From 

 this, and from the dimensions of the capillary tube, the tem- 

 perature of the gas can be approximately ascertained, pro- 

 vided that its specific heat does not alter much with the tem- 

 perature. 



From the older experiments of Gr. Wiedemann and the newer 

 ones of A. Naccari and Bellati, however, it follows that the 

 quantity of heat generated in each cross section of a discharge- 

 tube at the passing of the discharge is independent of the 

 magnitude of the section, and in very wide tubes is somewhat 

 less. It thence follows, further, that the increments of tem- 

 perature must be inversely proportional to the cross section, 

 and so the increments of temperature of the gas in the wider 

 tube can be calculated from those observed in the narrower 

 one. 



If p is the pressure of the gas, V the volume of the heated 

 gas in the capillary tube below the surface of the oil of tur- 

 pentine, z the number of discharges in a minute, Z the time, 

 in minutes, during which the discharges pass through the gas, 

 t the corrected increase of temperature generated in the calo- 

 rimeter, c the specific heat of the gas, s its specific gravity at 

 0°, w the waterworth of the calorimeter, then the increment 

 of temperature T of the gas, to be calculated from the above 

 quantities, at each discharge in the capillary tube is very 

 nearly 



T= tt#.760 g 

 YscpZz 



* For c I have introduced the specific heat at a constant pressure, 

 0*237. It might, however, be possible for the heating in a part, at least' 

 of the capillary tube to take place at constant volume ; the numbers found 

 for T and r would then become J higher. In face of this uncertainty the 

 error vanishes completely which we have committed in putting for s the 

 specific gravity at 0° and not that at the temperature of the experiment. 



