184 On the Electrical Behaviour of Solid Insulators. 



manifests itself in the opposite ways in which changes of tempe- 

 rature affect the electrical behaviour of each. 



Whereas a rise of temperature diminishes the conductivity of 

 solid conductors, electrical movements take place in insulators 

 much more quickly at high temperatures than at low ones, and 

 indeed very small variations of temperature exert a most marked 

 influence on the formation of the residual charge. 



It had been previously observed that glass became capable of 

 transmitting the galvanic current at 200° C. ; but that changes 

 of temperature, such as occur in our rooms, could affect in an 

 important degree the formation of the residual charge is a thing 

 which, so far as I am aware, no one had suspected. 



Experiment has, however, demonstrated that an elevation of 

 temperature from 10° to 20° C. lessens the, time in which the 

 same diminution of the charge takes place to one-half in the case 

 of a glass plate, and to one-tenth in the case of wax. 



As to the practical execution of these experiments, they were 

 all made in the Physical Institute of the University of Munich, 

 and by means of a Kohlrausclr's sine-electrometer. Since, how- 

 ever, the alterations frequently took place so quickly* that it 

 would have been impossible to make an observation according 

 to Kohlrausclr's method, it was needful to employ a slight (but, 

 as the author thinks, not unimportant) modification of the instru- 

 ment. 



This consisted in a divided paper scale suspended in the in- 

 side of the case. By reducing the values of the scale-divisions 

 by empirical comparison to the direct indications of the electro- 

 meter, it was possible to make observations without touching 

 the instrument. This arrangement enabled me, under favour- 

 able circumstances, to make ten observations in a minute, while 

 by the original method it was not possible, even in the most 

 favourable case, to make more than four readings in the same 

 time. 



The results obtained may be briefly stated thus : — 



(1) Electrical movements can take place in the interior of 

 insulators. 



(2) These movements are occasioned in part only by the 

 action at a distance of the electricities collected upon external 

 conductors. 



(3) They take place much more quickly at high temperatures 

 than at low ones. 



* With the thinnest plate (1*6 millim. thick) the charge sank in twenty 

 seconds from 100 to 15, and in sixtv seconds to - 92. 



