204 -Mr. Morgan’s Obfervations and Experiments on 
which efcape firft or moft eafily. The ele&rical brufh is 
always of a purple or bluifh hue. If you convey a fpark 
through a Torricellian vacuum, made * without boiling the 
mercury in the tube, the brufh will difplay the indigo rays. 
The fpark, however, may be divided and weakened even in 
the open air, fo as to yield the mod; refrangible rays only. 
exp. xi. To an infulated metallic ball, four inches in dia- 
meter, I fixed a wire a foot and a half long. This wire termi-* 
nated in four ramifications, each of which was fixed to a 
metallic ball half an inch in diameter, and placed at an 
equal diftance from a metallic plate, which communicated by 
metallic eondu&ors with the ground. A powerful fpark, after 
falling on the large ball at one extremity of the wire, was 
divided in its paflage from the four fmall balls to the metallic 
plate. When I examined this divifion of the fluid In a dark 
room, I difcovered fome little ramifications which yielded the 
indigo rays only : indeed, at the edges of all weak fparks the 
fame purple appearance may be difcovered. We may like wife 
obferve, that the nearer we approach the center of. the fpark* 
the greater is the brilliancy of its colour. But I would now 
with tolhew 
6. That the influence of different media on ele&rical light 
is analogous to their influence on folar light, and will help us 
to account for fome very Angular appearances. 
exp. xn. Let a pointed wire, having a metallic ball fixed to one 
of its extremities, be forced obliquely into a piece of wood, fo as 
to make a fmall angle with the furface of the wood, and to make 
* If the Torricellian vacuum is made with mercury perfeftly purged of air, it 
becomes a perfeft non-condu&or. This, I believe, will be proved decifively by 
feme experiments which I hope will be foon communicated to the Royal Society. 
Dr. Price., 
the 
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