of Electricity through Rarefied Air. 15 



Pressure of _. , 



the air. Distance between 



millim.' tne balls « 



117-5 1-30 



91-2 1-20 



68-3 1-15 



21-0 1-15 



14-1 1-12 



8-0 1-10 



6-1 0-95 



3-0 1-00 



2-38 1-05 



0-2 .... . 1-40 



In these last two series the minimum is found lower down 

 than in series 2 — namely, in the first between pressures of 

 2 and 4 millim ., and in the second between 3 and 8 millim. 

 This must probably be attributed to the distance between the 

 electrodes being 30 millim. instead of 5 as in series 2. If, 

 however, the pressure of the minimum be augmented to a 

 higher degree, the value increases more quickly when the dis- 

 tance is greater than when it is less. 



Experiment 5. The object of this experiment was to deter- 

 mine whether the electromotive force e is dependent on the 

 quantity of electricity traversing the spark in the rarefied-air 

 space. The electrodes consisted of platinum wires, the dis- 

 tance between which amounted to 30 millim. ; pressure of the 

 air 1*8 millim. A rheostat being inserted at iv (fig. 1) in the 

 wire that went to the galvanometer, a deflection of 12*6 scale- 

 divisions was obtained; while, if the rheostat was placed at p, 

 in the wire going to the spark, the deflection did not amount 

 to more than 7*1 divisions. When the rheostat was excluded 

 from the circuit, the deflection amounted to 42 divisions. 

 When the rheostat was intercalated at to, of course the quan- 

 tity of electricity passing through the spark was greater than 

 when the resistance was located at p, although the total resist- 

 ance of the closed circuit in the two cases was identical. 

 Consequently the electromotive force increases with the quantity 

 of electricity traversing the spark. These observations show, 

 further, as might have been expected, that the intensity of the 

 current xoill be diminished if a resistance be inserted in the closed 

 circuit. 



For the case of a constant current (from a sufficiently 

 powerful galvanic battery, for example) traversing the 

 rarefied-air space and producing there an electromotive force 

 e } we must take care not to draw from the foregoing result 



