Discharge of Electricity. 



401 



modes of discharge — by means of threads of solid particles, 

 by motion of the liquid, by a disruptive discharge, and by 

 motion of gas-bubbles. When a chain of particles was formed, 

 the index of the electrometer indicated the passage of a cur- 

 rent, which, when sufficiently great, broke the thread and 

 turned into a spark-discharge. The liquid was more easily 

 set in motion when its surface was not much above the upper 

 plate. The bubbles of gas were formed by the passage of the 

 spark. A disk, when used as the upper electrode, prevented 

 them from escaping ; and we observed that they were more 

 strongly repelled when the disk was electrified positively than 

 when negatively. At a diminished pressure they were ob- 

 served to effect the discharge by carrying the electricity with 

 them to the negative electrode. The bubble, when freely sus- 

 pended, was not spherical, but had its axis in the direction of 

 the line of force elongated. Similar phenomena were observed 

 in paraffin oil, a liquid paraffin, and olive oil. 



Measurement of the Difference of Potential required to pass a 

 Spark through a Liquid Dielectric at the Atmospheric Pres- 

 sure between Parallel Metal Plates at different Distances. 



We have investigated this experimental problem in the 

 cases of paraffin oil, oil of turpentine, and olive oil, for a length 

 of spark ranging from *1 to *4 centim. and, in the case of 

 the last, *5 centim. Two precautions were requisite in 

 making the observations: — one, to filter the liquid before begin- 

 ning, so as to get rid of all solid particles ; and the other, to 

 eliminate the gas-bubbles produced by one spark before ob- 

 serving for its successor. It was impossible to carry the series 

 of readings further than the above limits, because at the next 

 greater distance the electricity escaped from the conductor 

 and caused the image to be driven off the scale before the dis- 

 charge through the liquid took place. In each case the read- 

 ings gave a straight line, passing not exactly through the 

 origin, but having a small negative intercept on the axis of 

 ordinates. 



Liquid. 



Function for V. 





30G-4s- 6-1 

 332-4 s- 7-2 

 298 s-10 



Oil of turpentine 







The observations for paraffin oil are plotted on diag. 5. 

 Thus a liquid dielectric has the electrostatic force and the elec- 

 tric tension both sensibly constant. 



