V'OL, XLV.J '^* J PHILOSOrHICAL TRANSACTIOWS. 483 



excited in all bodies, but much stronger in some than in others ; and that, in 

 particular, they are not capable of being at all excited in metals by friction. 



3. The attractive and repulsive property will be stronger or weaker in any body, 

 in proportion to the quantity of excited effluvia with which it is impregnated. 



4. That those bodies which are most easily excited by friction, will receive the 

 least quantity of the electrical effluvia from any other excited body ; and, on the 

 contrary, metals, or those bodies in which they cannot be excited by friction, 

 will receive the most. 



From these observations he thinks it may be shown, that this appearance of 

 light is so far from proving that the effluvia come out of the non-electric, at whose 

 point they are visible ; that from thence it cannot be concluded the body has any 

 of the electrical matter residing in it, but is rather a proof to the contrary. For 

 the same appearance would be produced from the setting in of the effluvia into 

 the non-electric ; and this might be confirmed, if necessary, by a variety of ex- 

 periments. And as those bodies, at whose point this light appears the strongest, 

 afford us no signs of their having any of the electrical effluvia residing in them, 

 either by their attracting or repelling other bodies, or by their being capable of 

 being excited in them by friction, as in glass, &c. nor in short any sort of evidence 

 whatever, but what arises from this appearance ; may we not expect some better 

 proof of their being possessed of these effluvia, before we admit of their issuing 

 out of them ? 



But the true cause of this remarkable phenomenon he apprehends to be, the 

 different density of the effluvia at the extremities of the 2 bodies : for the effluvia 

 will be much denser at the extremity of a pointed body than at an obtuse one : 

 and as the force by which the particles endeavour to expand themselves, increases 

 in proportion to their density, it follows, that the particles will be reflected back 

 with greater violence from the pointed body than the other ; and this force ex- 

 ceeding the attractive power of that particular part of the feather, to which it is 

 directed, the fibres will be repelled by it ; whereas the force, with which the par- 

 ticles endeavour to expand themselves from the obtuse body, being less than the 

 attractive power, it follows, that the fibres of the feather will continue to be 

 attracted by it. 



Exper. Q. — Take two plates of metal, very clean and dry, whose surfaces are 

 nearly equal ; hang one of them horizontally to the electrified rod, and bring 

 under it on the other any thin light body, as leaf-silver, &c. ; when the upper 

 plate is made electrical, the silver will be attracted by It; and if the under plate 

 be held at a proper distance, will be perfectly suspended at right angles to the 

 plates, without touching either of them ; but if they be either brought nearer 

 together, or carried farther asunder, the leaf-silver will cease to be suspended, 

 and will jump up and down between them. The same effect will be produced, 



3 a "J iv , .c».ii."i 



