35* Dffcription ,of [Book IV. 



a cloud, and this is commonly termed the afcending 

 water-Jpout. 



A different explanation of thcfe phenomena hat 

 been, however, given by other philofophers, and to this 

 it will be proper to advert in the fucceeding book> 

 which treats of the nature and properties of air *. 



* Mr. Nicholfon, who has given both theories, has the follow- 

 ing obfervations, which greatly ftrengthen the hypothecs which. 

 afcribes thefe phenomena to electricity :- * It was obferved of 

 water-fpouts, that the convergence of winds, and their confequeut 

 whirling motion, was a principal caufe in producing that effeft; 

 but there are appearances, which caji hardly be foJved by fuppof- 

 ing that to be the only caufe. They often vanifh, and prefently 

 appear again in the fame place ; whitifh ox yellowifh flames have 

 fometimes been feen moving with prodigious fwiftnefs about them* 

 and whirlwinds are obferved to eleftrify the apparatus very ftrongly. 

 The time of their appearance is generally thofe months which are 

 peculiarly fubjeft to thunder-ftorms, and they are commonly pre- 

 ceded, accompanied, or followed by lightning, the previous itate of 

 the air being alike in both cafes. And the long eftablifhed cuf- 

 tom, which the failors have, of prefenting (harp fwords to difperfe 

 them, is no inconfiderablecircumftance in favour of the fuppofition 

 of their being electrical phenomena. Perhaps the afcending mo- 

 tion of the air, by which the whirling is produced, may be the 

 current known to iflue from ele&rified points, as the form of the 

 protuberance in the fea is fomewhat pointed; and the elcftrified 

 drop of water may afford confiderable light in explaining this ap- 

 'i vol. ii. p. 361. 



