VOL. LXII.] PHILOSOPHICAL TRANSACTIONS. 313 



for when that circumstance happened, they were very evidently affected in the 

 same manner. And found it more easy to discover the kind of electricity present 

 in the tube, by approaching excited wax to the balls of an electrometer, held at 

 a proper distance from the tube, than by applying it near the balls which hung 

 from the tube; for they generally diverged so much, that it was very difficult to 

 have in readiness a small tube of glass, or wax sufficiently excited to affect them. 



It has sometimes happened that the balls of the tin tube, &c. perfectly at rest, 

 have, in consequence of a flash of lightning, suddenly repelled each other, and 

 immediately after closed. As this circumstance has frequently happened when 

 the air was in a damp state, he sometimes imagined that the equilibrium be- 

 tween the earth and lower clouds had been quickly restored, on receiving the 

 electricity of the higher ones ; and at other times he supposed that it might be 

 owing to the lateral effect of the explosion. If two or more persons, at a suffi- 

 cient distance from each other, would correspond by signals, viz. a red flag for 

 positive, and a blue one for negative electricity, we should probably obtain, in 

 due time, more satisfactory certainty with regard to the electricity of the clouds, 

 thunder, &c. than has hitherto been given, or is perhaps possible for any one 

 man to acquire, without the aid of wires or chains, produced from different ap- 

 paratusses, placed at different distances from each other. 



Observations on the above, by Mr, Henley. — Mr. H. finds a fog (not very 

 thick) soon after its appearance, strongly electrical. The balls open 4- or ^ inch, 

 and close at the approach of excited wax, when brought within 10 inches of 

 themj if the wax is brought within 3 or 4 inches, they diverge again: as the 

 wax is withdrawn, they converge again, till it gets beyond the distance of its in- 

 fluence, when they begin to diverge again ; and, as the wax is withdrawn still 

 farther, they continue to open, in consequence of the electricity in the fog, till 

 they reach their original distance from each other. There is very little disturb- 

 ance by the wind, and the little there is, only wafts them in a small degree, but 

 they keep separate. If they are held near the tiling, or brick-work, of a neigh- 

 bouring house, they close; but begin to diverge again, at the distance of 3 or 4 

 feet from it; and their divergence increases, as they recede from the building, 

 till they separate -J- or ^ inch, as at first. 



October 3, 177 ij Mr. H. tried the electricity of a thick fog, and, in at least 

 20 different trials, found the balls separated from -i^ to -I- inch distance. When- 

 ever he brought them near the building, or approached them with a stick of 

 excited wax, they closed ; and opened again, on removing it. 



XIX. Observations on Different Kinds of j4ir. By Joseph Priestley, LL. Z>., 



F.R.S. p. 147. 

 This paper is reprinted in Dr. Priestley's works on different kinds of air^ 

 where ii may be consulted. , . ., " 



VOL. XIII. S s 



