32 Prof. G-. Quincke on Electrical Expansion. 



the original volume, the glass was generally perforated and the 

 apparatus broken. A change of volume of 68 millionths with- 

 out fracture was observed only with a particular kind of 

 German glass. 



12. Similar changes of volume were observed upon electri- 

 fying thermometer condensers of mica, quartz, and caoutchouc 

 filled with water. 



The changes of volume observed with many kinds of mica, 

 and with caoutchouc which had remained in contact with 

 water for a long time, were comparable with those observed 

 with glass ; but with fresh caoutchouc the change is about 

 ten times as much. 



13. In experiments with vessels of caoutchouc there is ob- 

 served at the same time a percolation of water through the 

 pores of the caoutchouc under the influence of the electricity. 



Alteration of Length wider the Influence of Electricity. 



14. Narrow glass tubes 1000 to 1200 millims. long were 

 coated inside and out with silver ; the two coatings were insu- 

 lated from each other and connected with the coatings of a 

 charged Ley-den jar. On charging such a tube condenser, 

 expansion took place, which disappeared again almost entirely 

 upon discharge. 



The expansion was measured best with Oertling's contact- 

 lever, by means of which an expansion of 0*004 millim. could 

 be measured directly, and a tenth of this amount could be es- 

 timated with certainty. 



The expansion Al of glass rods under electric influence, 

 already investigated by Righi*, takes places essentially ac- 

 cording to the same laws as the change in volume of the ther- 

 mometer condensers. Its magnitude increases with the length 

 I of the rod. 



The electric expansion -j- is nearly, but not exactly, pro- 

 portional to the square of the difference in electric potential of 

 the coatings of the tube condenser, and inversely proportional 

 to the square of the thickness of the glass. With a difference 

 of potential corresponding to a spark-distance of 2 millims. 

 between brass spheres of 20 millims. diameter, the electric ex- 

 pansion of tubes of English flint-glass varied from 2*26 to 0-72 

 millionths of the original length for the thickness of glass of 

 0-097 to 0-186 millim. 



15. Under similar circumstances the electric expansion was 

 the same, and attained its maximum in the same time, whether 

 the glass tubes were surrounded with air or water. 



* Comptes Eendus, lxxxviii. 1879, p. 1263. 



