VOL. XLV.] PHILOSOPHICAL TRANSACTIONS. 481 



together, and therefore become denser there than in any other part of the rod ; 

 and therefore, if the light be owing to the density and velocity of the effluvia, 

 it will be visible at the point, and no-where else. 



And that the light is thus produced, will appear by considering that whatever in- 

 creases or diminishes either the velocity or density of the particles, will increase 

 or diminish the light. For, if the motion of the wheel which turns the sphere 

 be stopped, the current of the effluvia will also be stopped, and the rays of light 

 will no longer be seen to issue from the point, and yet the whole rod will con- 

 tinue to be electrical ; but on putting the sphere again into motion, the effluvia will 

 become visible as before, and will increase as the sphere is more strongly excited. 

 Again, the light will be visible to a greater or less distance, as the point is more 

 or less acute; and this light is always brightest next the point, and grows fainter as 

 the rays diverge, this is plainly owing to the different density of the rays at equal 

 distances ; for when the point is more acute, the rays will diverge less, and there- 

 fore will be denser to a greater distance than when it is less acute. 



When a non-electric with flat end, is brought within a few inches of the point 

 of the electrified rod, the electric stream will be attracted by it, and the rays made 

 to diverge less than before; and the effect will be the same as if the point was 

 more acute; viz. a continuation of the light to a greater distance, and which will 

 be further increased by the additional velocity the particles will acquire from the 

 attraction of the non-electric. 



Mr. E. now endeavours, from the sameprinciples,toaccountforthosephenomena, 

 which are produced on a nearer approach of the non-electric to the electrified rod. 



Exper. 8. If the non-electric body, whether flat or pointed, be brought nearer 

 to the end of the rod, than in the last experiment, there will be a small stream of 

 light produced, reaching quite from the electric to the non-electric body, and if 

 brought still nearer, there will issue a spark, attended with a small snapping noise, 

 which will be succeeded by others at equal intervals ; and if the non-electric beheld 

 at some distance from the side of the rod, its point will often appear luminous, but 

 no part of the electrified rod will be so. * If it be brought nearer, there will likewise 

 be sparks produced at nearly equal intervals from each other, which will sometimes 

 appear as issuing from the side of the electrified rod, at others as coming from 

 the non-electric. If a finger be used as the non-electric, it will receive a smart 

 stroke; and if spirit of wine, heated so as to emit an inflammable vapour, be 

 made use of, it will be kindled by the spark. 



These phenomena may, on the afore-mentioned principles, be thus accounted 

 for. If the non-electric rod be pointed, and brought so near as, by its attrac- 

 tion, to prevent the rays issuing from the point of the electrified rod from 

 diverging, they will be drawn off parallel to each other, and consequently be 

 equally luminous throughout the whole distance between the two rods. 



VOL. IX. 3Q 



