a'04. Mr. Morgan's Obfervations and Experiments on 

 which efcape firft or moft eafily. The eleftrical brufh is 

 always of a purple or bluifh hue. If you convey a fpark 

 throuah a Torriceiriaii vacuum, made * without boilino- 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 conductors 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 wliich yielded the 

 indigo rays only: indeed, at the edges of all weak fparks the 

 fame purple appearance may be difcovered. We may likewife 

 obferve, that the nearer we approach the center of the fjpark,.' 

 the greater is the brilliancy of its colour. But I would now 

 "wifh tofhew | 



6. That the influence of diflferent media on electrical light 

 is analogous to their influence on folar light, and will help us. 

 to account for fome very fingular appearances. 



EXP.xii. 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-conduftor. This, I believe, will be proved decifively by 

 X©me experiments which I hope will be foon communicated to the Royal Society. 



Dr, Price, 



I the 





