430 . On the Aurora Borealis. [Dec. 



square of the tangent of the angle whose sine is - — - . Therefore if 



we call this angle t, the formula is changed into the following : — 

 log. y = log. 2 + log. a + log. m. + 2 log. t — 3 log. radius. 



Notwithstanding the ingenuity of this method, there are but few 

 observations that have been made which are adapted to it. The other 

 method consists in observing the position of the Aurora from two 

 different places; and as this is universally understood it would be 

 superfluous to give a detailed description of it here. 



The following table exhibits the height of the different Aurorae 

 Boreales above the surface of the earth that have been hitherto 

 measured, as far at least as 1 have met with them in the writings of 

 different philosophers : — 



He i glit in 

 Place. Observer. English Miles. 



Peinier Gassendi 566 



C Rome Bianchini ") ... 



\_ Copenhagen .... Horrebow j 



C Geneva Cramer 



\ Montpellier 



Petersburgh Kraft " 133 > 



Petersburgh Kraft 160 



Geneva 456 



"I 440 



C Copenhagen .... Horrebow \ 



I BreuiUe De Mairan J bbU 



$ Paris Buache \ ,.„„ 



£ Copenhagen Horrebow J 



C Paris Godin \ __ 



(_ Copenhagen Horrebow f 



$ Paris Godin \ .„_ 



£ Copenhagen Horrebow / 



S Paiis De Mairan \ ... 



(_ Copenhagen Horrebow ) 



£ Paris De Fouchy . . . . \ rr >. 



C Torneo Celsius J 



£ Paris De Fouchy . . . . \ „„ 



C Montpellier Plantade J 



$" Upsala Celsius \ .„„ 



C Havre de Grace . . De Mairan J 



C Paris De Fouchy . . . . \ .„_ 



C. Toulouse D'Arquier j ; 



Paris De Fouchy .... 466 



£ Paris De Mairan \ .„„ 



C Hague Gabry j 



Upsala Fernerus 1006 



£ Upsala Bergman ....... "1 5 „ 4 



t Hernosand Gisler J 



