VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. I75 



road^ and the dust struck up with a stick, near it, electrified it positively. 

 Breaking the glass tear on a book electrified it negatively, probably by friction in 

 the act of shivering, for when broken in water it did not electrify it. Wheat 

 flour, and red-lead, are strongly negative in all cases where the chalk is positive. 

 The following powders were like chalk : red and yellow ochre, rosin, coal 

 ashes, powdered crocus metallorum, aurum mosaicum, black-lead, lampblack, 

 (which was only sensible in the first two methods), powdered quick -lime, umber, 

 lapis calaminaris, Spanish brown, powdered sulphur, flowers of sulphur, iron filings, 

 rust of iron, sand. Rosin and chalk, separately alike, were changed by mix- 

 ture ; this was often tried in dry weather, but did not succeed in damp : white- 

 lead also sometimes produced positive, and sometimes negative, when blown 

 from a plate. 



If a metal cup be placed on the cap, with a red-hot coal in it, a spoonful of 

 water thrown in electrifies the cup negatively ; and if a bent wire be placed in 

 the cap, with a piece of paper fastened to it to increase its surface, the positive 

 electricity of the ascending vapour may be tried by introducing the paper into it. 

 Perhaps the electrification of fogs and rain is well illustrated by pouring water 

 through an insulated cullender, containing hot coals, where the ascending 

 vapour is positive, and falling drops negative. 



The sensibility of this electrometer may be considerably increased by placing a 

 candle on the cap. By this means a cloud of chalk, which only just opens the 

 leaf gold, will cause it to strike the sides for a long time together ; and the elec- 

 tricity, which was not before communicated, now passes into the electrometer, 

 causing the leaf gold to repel, after it is carried away. Even sealing-wax by this 

 means communicates its fire at the distance of 12 inches at least, which it 

 would scarcely otherwise do by rubbing on the cap. A cloud of chalk or wheat 

 flour may be made in one room, and the electrometer, with its candle, be after- 

 wards leisurely brought from another room, and the cloud will electrify it before 

 it comes very near. The air of a room adjoining to that in which the electrical 

 machine was used, was very sensibly electrified, which was perceived by carrying 

 the instrument through it with its candle. 



In very clear weather, when no clouds were visible, the electrometer has been 

 often applied to the insulated string of kites without metal, and their positive 

 electricity caused the leaf gold to strike the sides ; but when a kite was raised in 

 cloudy weather, with a wire in the string, and when it gave sparks about a quar- 

 ter of an inch long, the electricity was sensible by the electrometer at the 

 distance of 10 yards or more from the string ; but when placed at the distance of 

 6 feet, the leaf gold continued to strike the sides of the electrometer, for more 

 than an hour together, with a velocity increasing and decreasing with the density 

 or distance of the unequal clouds which passed over. Sometimes the electricity 



