DISRUPTIVE DISCHARGE OF ELECTRICITY. 681 
TABLE IT.—Oil of Turpentine, 18th June 1878. 



Length of Spark Difference of Mean Difference 
in Centimetres. Deflection. Zero. Potential. of 
3: n. nv. v—n. Potential. 
383 458 75 \ 
= (390 ; 68 ra 
§ 300 ¢ 158 
z | 290 4 168 Los 
F 200 a 258 
: | 200 i 258 298 
: 110 a 348 
: | 105 ‘ 353 ay 
45) —-4.()* 290. 


Before putting in the liquid we took readings for sparks through the air, 
and we have plotted them along with the above in diagram 2. The curve for 
turpentine is precisely similar to that for paraffin. We deduce— 
V = 922 s—20, 
where V denotes the relative difference of potential, and s the length of the 
spark. Hence— 
R = 922, 
that is, the electrostatic force is constant. In absolute measure R = 338C.G.S. 
units. 
Thus, in the case of a liquid, the electrostatic force is constant ; while in 
| the case of a gas it is variable; and this is, probably, because the liquid 
cannot be condensed on the surfaces of the electrodes, while the gas can. 
Liffect of Heating the Electrodes upon the Passage of the Electric Spark. 
For the purpose of studying minutely the effect of heating the electrodes 
upon the passage of the spark, we constructed an apparatus suggested by 
| Professor CLerk Maxwett. Two pieces of thick platinum wire, p p (fig. 1), 
| Were insulated in a brass plate b, by means of vulcanite plugs v7, and placed so 
- * Escape from the connections of the positive conductor of the Holtz began. 
