On the Electrical Phceti07nena exhibited in Vacuo, 185 



the passage of the electricity of the charged Leyden phial 

 through the vacuum produces. 



When the intense heat produced by electricity is considered, 

 and the strong attractive powers of differently electrified sur- 

 faces, and the rapidity of the changes of state, it does not seem 

 at all improbable, that the superficial particles of bodies, which, 

 when detached by the repulsive power of heat, form vapour, 

 may be likewise detached by electrical pov»ers, and that they 

 may produce luminous appearances in a vacuum, fiee from all 

 other matter by the annihilation of their opposite electrical 

 states. 



In common cases of electrical action, the quantity of the heat 

 generated by the anniliilation of the different electrical states 

 depends, as I stated in my last communication to the Society, 

 upon the nature of the matter on which it acts; and in cases 

 when electrical sparks are taken in fluids, vapour or gas is al- 

 ways generated ; and in elastic fluids, the intensity of the light 

 is always greater, the denser the medium. The luminous ap- 

 pearances therefore, it is evident from all the statements, must 

 be considered as secondary ; whilst the uniform exertions of 

 electrical attractions and repulsions, under all circumstances, 

 in rare and dense media and hi vacuo, and with respect to 

 solids, fluids, and gases, point them out (whether they be sj>e- 

 cific affections of a subtile imponderable fluid, or peculiar pro- 

 perties of matter) as primary and invariable electrical plijieno- 

 mena. 



I have mentioned in the last page the suspicion, that melted 

 tin may contain air. I sliall conclude this paper by stating the 

 grounds of this suspicion, and noticing a circumstance which 

 appears to be of considerable importance, both in relation to 

 the construction of barometers and thermometers, and to the 

 anal3'sis of gaseous bodies. Recently distilled mercury that 

 has been afterwards boiled and cooleil in the atmosphere, and 

 which presents a perfectly smooth surface in a barometer tube, 

 emits air when strongly heated in vacuo, and that in quantities 

 sufficient to cover the whole interior of the tube with globules; 

 and on keeping the stop-cock of one of the tubes used in the 

 experiments on the mercurial vacuum open for some hours, it 

 was found that the lower stratum of mercury had imbibed air, 

 for when heated in vacuo, it emitted it distinctly from a space 

 of a (jiiarter of an indi of the column: smaller (|uantities were 

 disengaged from the next part of the cohnun ; and its pro- 

 duction ceased at about an inch high in the lnl)e. There is 

 great reason to believe, tiiat this air exists in jnercury in the 

 same invisible state as in water, that is, distributed through its 

 pores; and the fact shows ihe necessity ol long boiling the 



V'«I. 00. No. 293. .SVy^/. 1822. A a jucrciuv 



