the Light of Bodies in a State of Comhuflion, 203 



infulated fubftance. I brought the ball within the ftriking 

 diftance of my conductor, and the fpark in pafling from the con- 

 ductor to the ball appeared very brilliant ; but the whole length 

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

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

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

 it was bright, but, when dittufed over the furface of air which 

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

 it?:w only in a dark room. If I leflened the furface of air 

 which received the fpark by fhortening the thread, I never 

 failed to increafe the brightnefs of the appearance. 



EXP. IX. To prove that the faintnefs of the electric 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 (hall find a brilliancy as great as 

 in the open air, 



EXP. X. Into a Torricellian vacuum, 2,^ inches in length, I 

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

 €xhaufl:ed tube, if it were inverted in water. This quantity of 

 air afforded refinance 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- 

 fiances through which it pafles with difficulty, depends oa 

 principles fimilar to thofe which account for the preceding fa<5tSo 

 I would now proceed to fhew, 



5. That in the appearances of ele£i:rlclty, as well as in thofe 

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

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



D d 2 %vhick 



