Emission of Xegatively Electrified Corpuscles. 253 



About 3000 grammes of mercury were placed in a glass 

 beaker, and some cotton silicate was placed in the same 

 beaker above the mercury ; above the cotton silicate was 

 a cardboard disk which covered the silicate entirely, except 

 that a space was left for the insertion o£ the thermometer, 

 and a little space was allowed for the edge of the disk to 

 clear the sides of the beaker. On pressing down the disk 

 the cotton silicate was suddenly immersed in the mercury, 

 and in some experiments there was a fall of temperature 

 amounting to *016° C. But the results were not consistent, 

 for in other experiments there was a slight rise of tempera- 

 ture, caused probably by the cotton silicate being at a higher 

 temperature than the mercury. After leaving the cotton 

 silicate immersed in the mercury for some time, so as to take 

 the same temperature, it was suddenly released, and a rise of 

 temperature was the invariable result. With 11 grammes 

 of cotton silicate the rise of temperature was about *02° C, 

 and with 30 grammes of silicate the rise of temperature was 

 about "05° C, but the results varied considerably. 



These experiments do not lend themselves to quantitative 

 measurement, for the surface of the mercury cannot be deter- 

 mined. When the filaments of cotton silicate are put into 

 mercury they tend to cling together in bundles or tufts, and 

 the mercury breaks up into a great number of little globules 

 between the tufts of silicate. The surface exposed by the 

 mercury is thus large and indeterminate. The results show, 

 however, that the sudden contraction of a mercury surface 

 causes an evolution of heat and corresponding rise of tempe- 

 rature, and the effect can be regarded as a modification of 

 the Pouillet effect for a liquid which does not wet, or enter 

 into intimate contact with the solid. 



H.M. Dockyard School, Portsmouth, 

 March 1902. 



XXVIII. On some of the Consequences of the Emission of 

 Negatively Electrified Corpuscles by Hot Bodies. By J. J. 

 Thomson, M.A., F.R.S., Cavendish Professor of Experi- 

 mental Physics, Cambridge*. 



IT was shown by Elster and Geitelf that an incandescent 

 metal wire in a good vacuum emits negative electricity; 

 in 1899 I showed that the carriers of this negative electricity 

 were * ; corpuscles/' i. e. were identical with the carriers of 



* Communicated by the Author. 



t Elster and Geitel, Wied. Ann. xxxvii. p. 315.^ 



