408 PHILOSOPHICAL TRANSACTIONS. [aNNO 1747. 



wood does not contract or dilate lengthwise with heat or cold. I am told that 

 Mr. George Graham is about making this experiment, as I am also, in order to 

 regulate pendulums. — I fear that Boerhaave's wet linen, which is so thin, may 

 begin to freeze before all the mercury or spirit of wine in the ball of the ther- 

 mometer has the same degree of cold ; though hanging there long before and after 

 freezing will bring it pretty near. — " A rod of iron 3 feet long will have about -J- 

 inch increase," or -j-H- P^rt. 



Continuation of a Paper concerning Electricity. By fVilliani IValson, F. R. S. 

 printed in these Trans. N° 477,* p. 695. 



As water is a non-electric, and of consequence a conductor of electricity, there 

 was reason to believe that ice was endowed with the same properties. On making 

 the experiment, Mr. W. found his conjectures not without foundation ; for on 

 electrifying a piece of ice, wherever the ice was touched by a non-electric, it 

 flashed and snapped. A piece of ice also held in the hand of an electrified man, 

 as in the beforementioned processes, fired warm spirit, chemical vegetable oils, 

 camphor, and gunpowder prepared as before. 



Prop. 1. — In common with magnetism, electricity counteracts, and, in light 

 substances, overcomes the force of gravity. Like that extraordinary power like- 

 wise, it exerts its force in vacuo as powerfully as in open air; and this force is 

 extended to a considerable distance through various substances of different textures 

 and densities. 



Carol. — Gravity is the general endeavour and tendency of bodies towards the 

 centre of the earth ; this is overcome by the magnet with regard to iron, and by 

 electricity with regard to light substances both in its attraction and repulsion; 

 but Mr. W. has never been able to discern that vortical motion, by which this 

 effect was said to be brought about by the late Dr. Desaguliers and others, having 

 no other conception of the manner of its acting than as rays from a centre, 

 which indeed is confirmed by several experiments : one of which, very easy to be 

 tried is, that if a single downy seed of cotton-grass be dropped from a man's 

 hand, and in its fall come within the attraction of the rubbed tube, the down of 

 this seed, which before seemed to stick together, separates, and forms rays round 

 the centre of the seed. Or if you fasten many of these seeds with mucilage of 

 gum Arabic round a bit of stick, the down of them, when electrified, which 

 otherwise hangs from the stick, is raised up, and forms a circular appearance 

 round the stick. As these light bodies are directed in their motions only by the 

 force impressed upon them, and as their appearance is constantly radiatim, such 

 appearance by no means squares with our idea of a vortex. 



* See p. 151 of this volume. 



