OP TEE AURORA BOREALIS. 41 



of an aurora which occurred in England in 1720, deemed to be exceedingly accu- 

 rate, from the exact correspondence of the appearances to those now witnessed in 

 the highest class of auroras ; but his reasoning on the cause is sufficiently crude. 

 The auroral bank of vapors usually seen acting on the northern horizon at the 

 commencement of a great display, he ascribes to a mixed mass of exhalations ; the 

 streamers, to the fermentation of the mass ; their inclined direction, to the prevail- 

 ing wind; and the waves, to irregular gusts of wind blowing upon and shaking the 

 columns. But Coates was an able geometrician, and we find in this paper the first 

 illustration, upon the true principles of perspective, of the mode of formation of 

 auroral arches, by the projection and superposition of parallel columns; a method of 

 illustration afterwards adopted and considerably extended by Dalton. 1 



Other writers of that age, ascribe the auroral lights to a nitro-sulphurous vapor, 

 a mixed mass of nitre and sulphur in a state of comminution, and, therefore, pos- 

 sessing the properties of gunpowder; 2 which vapor was supposed to rise above the 

 clouds, where it was kindled by pressure and motion, and subjected to continued 

 explosions ; and hence the agitation, smoky vapor, peculiar sounds, and bright 

 flashes of the aurora. 3 



In the year 1733, was published the great work of Mairan on the aurora borealis. 4 

 Mairan was a leading member of the French Academy, and one of the ablest philo- 

 sophers of his time. His work bears internal evidence of great research, guided by 

 superior powers, and a competent knowledge of the laws of nature, so far as they 

 had then been unfolded. It contained a full history of the aurora borealis,. as far 

 as it could be gathered from the records of past ages, and proposed an original 

 theory, which the author illustrated and defended with great ability. He ascribed 

 the aurora to the zodiacal light, the outer portions of which, according to him, the 

 earth traverses at certain periods in its revolutions around the sun, attracting to 

 itself the matter of the zodiacal light, which mingles with its atmosphere, and pro- 

 duces the various phenomena of the aurora. Mairan, therefore, appears to have 

 been the first to propose the doctrine of the cosmical origin of the aurora bore- 

 alis. Respecting the nature of the zodiacal light itself, he adopted the common 

 opinion, that it is the sun's atmosphere ; but this hypothesis scarcely affects his 

 conclusions, in assigning it as the cause of the auroral exhibitions, since the 

 existence of the cause assigned is unquestionable, whatever views may be enter- 

 tained of its relations to the sun. This theory was embraced by some of the ablest 

 philosophers of the day, and opposed by others equally eminent; but on the dis- 

 covery of the identity between electricity and lightning, and after the agency of 

 atmospherical electricity in the phenomena of thunder-storms was proved, and espe- 

 cially after the resemblance was recognized between the flashes of electricity in an 



1 Phil. Trans., No. 365, or abridged, VI, 82. 



2 Phil. Transactions, No. 395, or abridged, VI, 94. 



3 The most complete and precise description of any of the auroras of that remarkable period, was 

 given by Professor Greenwood, of Harvard University, of an aurora which occurred October 22d, 

 1730, published iu the Philosophical Transactions, No. 418, or abridged, VI, 115. 



4 The first edition was issued in 1733, in 12mo. A second edition, greatly enlarged, was published 

 in 1754, in 4to. 



6 



