Obfervations on "Fire Balls. 73 



J I. Only a few of them had an apparent motion round 

 their axes*. 



12. The greater part of them diffufed a very lively dazzling 

 light t ; the fewer number a faint light. Their colour and 

 fplendour were very different and variable ; fometimes red, 

 fometimes blue, fometimes violet, fometimes in part yellow 

 or dazzling white, and fome exhibited the prifmatic colours J. 

 Several have been feen to burn with a bright flame, and 

 others as if in a ftate of ignition. 



13. Their real diameter, as far as could be ascertained, 

 fometimes bv conjecture and fometimes by actual meafure- 

 ment, was always very confiderable. The diameter of that 

 reflecting which Sir John Pringle made calculations from 

 various obfervations he collected, and of that feen by Mr. 

 Rittenhoufe § at Philadelphia, in the month of October 1779, 

 were at molt about half a German mile. 



14. They feem to have originated at a very different, 

 though molt of them at a very confiderable height above the 

 furface of the earth. At any rate all of them, whofe mean 

 or greateft height was fubjected to any calculation, exceeded 

 that of the higheft clouds, as clouds are fcarcely perceptible 

 at the height of 13,500 toifes ; and Silberfchlag found the 

 greateft height of the fire-ball, which appeared in July 

 1762, to be 19 German miles, or 72,276 toifes. On this 

 account their origin, as Reimarus and Chladni have already 

 fufficiently (hewn, is not to be afcribed merely to electricity, 

 though fome have confidered them as occafioned by the 

 action of the electric fluid between the clouds and the 

 northern lights, which would agree exceedingly well with 



* Nova Attn Nit. Curiof. vol. i. p; 348. Thcorie der am 23 ftcn. 

 Jul. 1762 erfchienenen Fcucrkugel ron J. E. Silberfchlag. Magd. Stcnd. 

 u. Leipz. 1764. 4. 



f Philofoph. Tr-mfaftions, vol. xli.part 1. p. 346. 



•thai&hes Magazin, vol. iv. part 2. p. 164. Hannbvrifches Maga- 

 zin, 1791, p.. 1627. 

 •§ Tranfidions of the American Pailofoph. Society, vol. ii. p. 175. 



their 



