480 PHILOSOPHICAL TRANSACTIONS. [aNNO 1747-8, 



are put into motion, and separated from it. 2dly. That the particles composing 

 these effluvia strongly repel each other. 3dly. That there is a mutual attraction 

 between these particles, and all other bodies whatever. 



The particles of these effluvia are so exceedingly small, as easily to pervade the 

 pores of glass, as is evident, in that a feather, or any light bodies inclosed in a 

 glass ball hermetically sealed, will be put in motion on the excited tube being 

 brought near the outside of it ; and it has been generally thought that they pass 

 through the pores of the densest bodies; and there are several experiments which 

 render this supposition not improbable ; though he acknowledges he has not yet 

 met with any one that he thinks quite conclusive. 



i: He now proceeds to show how, from these principles, the phenomena of 

 some of the more remarkable experiments of electricity may be accounted for. 



Exper. 7. Let a rod of iron, pointed at one end, be suspended on silk lines, 

 as in exp. the 6th, and by the sphere be made electrical. When the rod is 

 strongly electrified, a stream of light in diverging rays will be seen to issue from 

 its point; and if any non-electric body be held a few inches from the point, the 

 light will become visible to a greater distance; and if the non-electric body be 

 likewise pointed, a light will seem to issue from that in diverging rays in the same 

 manner as from the electrified rod. But if the non- electrical body be fiat, and 

 held at the same distance from the rod as the pointed one was, no light will be 

 seen to come from it. 



The principal phenomena to be accounted for in this experiment are; why a 

 light is only seen at the point of the rod, and not through the whole length of it? 

 why the light is visible to a greater length, when the point is approached by a 

 non-electric? and, why a light is seen to issue from the non-electric when it is 

 pointed, and not when it is flat. 



On which he observes, that whenever the sphere is excited, the electrical ef- 

 fluvia are put into motion, and made to form an atmosphere round about it; 

 whence, by their repulsive property, they endeavour to expand themselves on all 

 sides equally ; but being strongly attracted by the iron, a great part of them are 

 drawn off along the rod, about whose surface they likewise form an atmosphere, 

 which will be denser or rarer, in proportion as the attraction of the rod is greater or 

 less; and as the repulsive power of these effluvia will always increase in propor- 

 tion with their density, it will follow, that whenever the sphere is so strongly ex- 

 cited, that the effluvia surrounding it are denser than those surrounding the rod, 

 they will, by their repulsive property, drive the effluvia off from the end of it in 

 a stream, and that with a very great velocity; as is evident, from their striking 

 against the hand like a blast of wind when brought near the end of the rod : and 

 as this velocity is partly owing to the attraction of the rod, so this attraction 

 continuing quite to the end of it, the velocity of the particles will there be 

 greatest; and as they approach towards the point, they will be brought nearer 



