the Light of Bodies in a State of Comhujlion, 203 



infulated fubftance. I brought the ball withui the ftrlking 

 diftance of my condu^lor, and the fpark in pading from the cou- 

 du^lorto the ball appeared v^ery brilliant ; but the whole length 

 of the filver thread appeared faintly luminous at the fame in- 

 ilant. In other words, when the fpark was confined within 

 the dimenfions of a fphere one-eighth of an inch in diameter, 

 it was bright, but, when difriifed over the furface of c^ir which 

 received it from the thread, its light became fo faint as to be 

 {&t\\ only in a dark room. If I leflened the furface of air 

 which received the fpark by ihortening the thread, I never 

 failed to increafe the brightnefs of the appearance. 



EXP. IX. To prove that the faintnefs of the eledtric light in 

 'vacuo depends on the enlarged dimeniions of the fpace through 

 which it is difFufed, we have nothing more to do than to in- 

 troduce two pointed wires into the vacuum, fo that the fluid 

 may pafs from the point of the one to the point of the other, 

 when the diftance between them is not more than the one-tenth 

 of an inch. In this cafe we ihali find a brilliancy as great as 

 in the open air. 



EXP. X. Into a Torricellian vacuum, 36 inches in length, I 

 conveyed as much air as would have filled two inches only of the 

 exhaufted tube, if it were inverted in water. This quantity of 

 air afforded refiftance enough to condenfe the fluid as it pafled 

 through the tube into a fpark 38 inches in length. The bril- 

 liancy of the fpark in condenfed air, in water, and in all fub- 

 flances through which it paiTes with difficulty, depends on 

 principles iimilar to thofe which account for the preceding fa(^s. 

 I would now proceed to fhew, 



5. That in the appearances of ele£lriclty, as well as in thofe 

 of burning bodies, there are cafes in which all the rays of light 

 do not efcape ; and that the mofl refrangible rays are thofe 



D d 2 which 



