f 



the hight of Badics ?/? a Siate of Cornkfrju^ z-^t 



did In a barometer at the fltme inftant, owing to the Yapour 

 which was formed by the water. But through this rarefied wa- 

 ter the ele£lrical fpark palled as luiniiioudy as ii; does through 

 air equally rarefied. 



EXP. V. If, inflead of water, a few drops of fpirits of wine ari 

 placed on the furface of the mercury, phi^enomena fimilar to 

 thofe of the preceding experiment will be difcovered, with 

 this difference only, that as the vapour in this cafe is more 

 denfe, the ele6lrical fpark in its paffage through it is not q^uite 

 fo luminous as it is in the vapour of water. 



EXP. VI. Good aether fubftituted in the room of the fpirits 

 of wine will prefs the mercury down fo low as the height of 

 1 6 or 17 inches. The eledrical fluid in pafling through this 

 vapour (unlefs the force be very great indeed) is fcarcely lumi- 

 ,nous. But if the preffure on the furface of the mercury in the 

 bafon be gradually leflened by the aid of an air-pump, the va- 

 pour will become more and more rare, and the eledric fpark in 

 pafling through it more and more luminous. 



EXP. vii. I could not difcover that any vapour efcaped from 

 the mineral acids when expofed in vacuo, To give them, 

 therefore, greater rarity or tenuity, I found different methods 

 neceflary. With a fine camel-hair pencil, dipped in the vi- 

 triolic, the nitrous, or the marine acid, I drew upon a piece of 

 glafs a line about one-eighth of an inch broad. In fome in- 

 ftances I extended this line to the length of 27 inches, and 

 found that the contents of an elecShric battery, confifliing of la 

 pint phials coated, would pafs over the whole length of this 

 line with the greatefl brilliancy. If by widening the line, or 

 by laying on a drop of the acid, its quantity was increafed 

 in any particular part, the charge, in paffing through that part, 

 never appeared luminous. Water, fpirits of wine, circum- 

 Vol. LXXV. D d flanced 



