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miles in thicknefs, as in the atmofphere, may be quite lumi- 

 nous, though the light from it be diminifhed by the diftance 

 from the eye. The light was fainter in every degree of the 

 rarefadlion, when there was moiflure in the tube, from my 

 having put a little bit of wet leather in the rec^ (which how- 

 ever was dried in the exhauftion ;) and this inclines me to 

 think, that it is air burnt and exploded in its paffage which 

 makes the eledtric matter vifible ; and that were there no air, 

 if it could pafs at all, it would not be luminous : for though 

 we were to fuppofc, that the eledlric matter would be ren- 

 dered luminous by mere watery vapour without any air ; yet 

 I imagine the extreme cold, in very elevated regions of the 

 atmofphere, would freeze this vapour, as it docs near the earth, 

 and condenfe it into icicles, deftroying its elafticity ; fo that 

 it could not afcend, by its expanlive force, beyond that height, 

 in which there would ftill be air, though of great tenuity : 

 if thefe things be fo, the Aurora BoreaJis is confined within 

 our atmofphere. 



N. B. The pear-gage with its metal cafe and wire, being 

 ' within the rec' prevented me from knowing what would be the 

 appearance of the eledlric matter in pafling through it. 



I HAD not an eledlrical machine mounted; fo could not in 

 thefe experiments try the efFed; of continual eledrification, and 



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