2^4 Mr. MoRGAN^s Obfervat'wtu and Experiments on 



which efcape firft or moft eafily. The ele£lrical brufli Is 

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

 through a Torricellian vacuum, made * withGiit boiling the 

 mercury in the tube, the brufh will difplay the indigo ra\^s. 

 The fpark, however, may be divided and weakened even in 

 the open air, fo as to yield the moil 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 condu6lors with the ground. A powerful fpark, after 

 falling on the large ball at one extremity of the wire, was 

 divided in its paffage 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 likewife 

 obferve, that the nearer we approach the center of the fpark,. 

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

 wifh to (hew 



6. That the influence of different media on electrical light 

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

 to account for fome very Angular 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 perfect non-condu6lor. This, I believe, will be proved decifively by 

 iftme experiments whicli I hope will be foon communicated to the Royal Society. 



Dr. Price. 



I the 



