Prof. G. Quincke on Electrical Expansion, 31 



liquid in the tube was observed by the aid of a horizontal mi- 

 croscope provided with a micrometer-eyepiece ; and the dimen- 

 sions of the apparatus were so chosen that a change in volume 

 of To-g oo o o oo °f the original volume could be observed. 



The change of volume Av is greater the larger the volume 

 v of the bulb of the thermometer is. The change in volume 

 follows instantaneously with flint-glass, more slowly with 

 Thuringian glass (which is a better conductor of electricity). 

 Upon discharge, the fluid returns nearly to its original posi- 

 tion, immediately in the case of flint-glass, more slowly with 

 Thuringian glass. 



5. The residual displacement (in the same direction as the 

 original displacement) after discharge is very small with flint- 

 glass and larger with Thuringian glass, and appears to depend 

 upon the electric polarization of the glass. 



6. Under similar circumstances, the change of volume is 

 greater only by an insignificant amount when the thermometer 

 is filled with mercury instead of water. 



7. The volume of the exterior of the thermometer-bulb in- 

 creases simultaneously with the interior and to the same 

 extent. 



8. If the outer surface of the thermometer-bulb be covered 

 with a thin layer of silver, the change of volume produced by 

 electric force is the same, whether the bulb be surrounded by 

 water or by air. 



9. This change of volume is almost entirely independent of 

 hydrostatic pressure of the fluid on the walls of the bulb. 



10. With the same apparatus, under apparently identical con- 

 ditions, the change of volume is sometimes greater and some- 

 times less, according as the glass has remained a longer or a 

 shorter time without being charged with electricity. 



At 



11. The expansion — is nearly, but not exactly, propor- 

 tional to the square of the difference in electric potential of the 

 two coatings of the thermometer-bulb, and inversely propor- 

 tional to the square of the thickness of the walls of the ther- 

 mometer-bulb. 



With English flint-glass and a thickness of glass of from 

 0*142 to to 0*591 millim., the change in volume varied from 

 10*67 to 0*19 millionths of the original volume, with a spark- 

 distance of 2 millims. between spheres of brass of 20 millims. 

 diameter. With an equal spark-distance, the change in volume 

 for Thuringian glass varied from 4*61 to 0*36 millionths of 

 the original volume with a thickness of glass from 0*238 to 

 0*700 millim. 



With greater change of volume than 10 to 12 millionths of 



