Chap. 6.] Aurora Bortalls. 35$ 



center, this being formed firft in the higher Re- 

 gions, and the furface being collected in the lower. 

 Agreeably to this, it is obferved, that on mountains, 

 hail-ftones as well as drops of rain are very fmall, 

 there being but a fmall fpate through which they 

 can fall. 



Clouds of fnbw differ in nothing from clouds of 

 tain, but iti the circumftance of the cold which freezes 

 trrem. Both the regular diffufion of fnow, and the 

 regularity of the parts of which it confifts, fiiew the 

 clouds of fnow to be actuated by fome uniform caufe 

 like electricity *. 



Confident with this theory is the fact, that vapours 

 never rife to a great height without producing me- 

 teors. Almoft all volcanic eruptions are accompa- 

 nied with lightning. The column of vapour, which 

 proceeds from the bowels of a volcano, is continually 

 traverfed by lightning, which fometimes feems to pro- 

 ceed from the higher regions, fometimes from the co- 

 lumn itfelf. Thefe lightnings were obferved by the 

 younger Pliny, in the eruption which killed his uncle ; 

 and Sir William Hamilton has obferved them feveral 

 times. The aurora borealis is alfo generally fuppofed 

 to be electrical -, its light feems to be produced by the 

 electric fluid, while it is condenfed in palling in the 

 columns of elevated vapour f. 



It 



* Prieftiey's Hift. Elert. vol. 1. 



} Mr. Adams's defcription of this meteor, in his Lectures, Is 

 as follows : ' The appearances of the aurora come under four dif- 

 ferent descriptions. ift, A horizontal light, like the morning 

 aurora, or break of day. 2dly, Fine, {lender, luminous beams, 

 Well denned, and of denfe light. Thefe often continue a quarter, 

 an half, or a whole minute, apparently at reft, but oftener with a 

 quick lateral motion. 3dly, Flaihes pointing upward, or in the 

 fame direction as the- beams, which they always fucceed. Thefe 

 are only momentary, and have no lateral motion ; but they are 

 A a 2 generally 



