558 LECTURE LVII. 



the experiments of Beccaria* and Cavallof that the air is in general 

 positively electrical, and most so in cold and clear weather ; in cloudy- 

 weather more slightly : and that during rain, the air is generally in a nega- 

 tive state. Mr. Read J has found that air charged with putrid vapours of 

 any kind, and in particular the air of close rooms, is almost always nega- 

 tively electrified. The electricity is more readily communicated to an 

 electrometer in an elevated situation, and in damp weather, than in other 

 circumstances ; a candle is also very useful in collecting it. When a wire 

 is connected with a kite, being continued along the string, we may fre- 

 quently ohtain from it sparks a quarter of an inch long. 



We find a complete and interesting description of the effects of a violent 

 thunder storm in a paper by Mr. Brereton, inserted in the Philosophical 

 Transactions^ The circumstance happened in September 1780, at East 

 Bourn, in a house occupied by Mr. Adair : it was built of stone, and stood 

 facing the sea. About nine o'clock, in a very stormy morning, a black 

 cloud approached the house ; several balls of fire were seen to drop from it 

 successively into the sea, and one in particular, appearing like an immense 

 sky rocket, broke against the front of the house in different directions. 

 Mr. Adair was standing at a window on the first floor, with his hands 

 clasped together, and extended against the middle of the frame : his hands 

 were forced asunder, he was thrown several yards off on the floor, and 

 remained for some time speechless and motionless, although not insensible 5 

 his clothes were much torn ; several articles of metal about his person were 

 partially melted, while others, apparently in similar circumstances, and in 

 particular a silver buckle, escaped ; and his skin was in many parts much 

 scorched and lacerated. The whole of the glass in the window, and a pier 

 glass near it, were completely destroyed, and scattered about the room ; 

 most of the furniture was broken to pieces, and all the bell wires were 

 melted. In the room above this, a lady and her maid were driven to a 

 distant part, and rendered insensible for some time, but not hurt ; in the 

 room below, two servants, who were near the windows, were struck dead : 

 both the bodies were turned black : one of them had a wound near the 

 heart ; and neither of them became stiff after death ; a third servant, who 

 was a little behind one of them, escaped with the loss of a telescope, which 

 he held in his hand, and with the sensation of a violent pressure on his 

 head and on his back. A large stone was forced out of the wall near them, 

 and thrown into the room, and some other similar effects were observed, 

 which marked the progress of the explosion. 



For guarding against accidents so dreadful, Dr. Franklin's great invention 

 of metallic conductors may be very advantageously employed : for, when 

 properly fixed, they afford a degree of security which leaves very little room 

 for apprehension. A conductor ought to be continued deep into the earth, 



* Delia Elettricita Terrestre Atmosferica, 4to, Torino, 1775. 

 f Ph. Tr. 1776, p. 407 ; 1777, p. 48. 



J Jour, of Electricity, Ph. Tr. 1792, p. 225 ; 1794, pp. 185, 266. Treatise on 

 Atmospheric Electricity, 1793. See Arago, Annuairefor 1838. 

 1781, p. 42. 



