410 Descripfion of the Aurora Borealis 



Add, that these lines are luminous, and varied in colour from 

 white to yellow, red, and crimson, and, sometimes, perhaps, tb 

 purple and to violet ; that they play, in the lower heavens in 

 a field of light, and in the upper over a sky of blue ; and the 

 picture of the Aurora Borealis is well nigh complete. The ob- 

 servation in the ninth sentence, that the vast columns, of which, 

 upon some occasions, the Aurora displays the forms, are of a 

 deep yellow upon one side, which, upon the other, fades gr^l- 

 dually into that of the sky, is to be understood, as expressing, 

 that, as in the late example, the outer edges of the columns, 

 or those next the dark or unillumined portion of the horizon, 

 are sharp and strongly defined ; while the inner ones are less 

 distinguished from the general field of light in which they 

 stand; and which distinction, after all, is but a delusion of 

 the eye, which more readily distinguishes the variation of 

 colour in the outer edge, which is so strongly relieved by the 

 dark and colder-coloured part of the sky, than the colour of the 

 inner part and edge of the column, which, more or less, ap- 

 proaches that of the ground behind it. 



5. Sentences seven and eight appear to the present writer 

 to convey the most accurate description possible, of the appear- 

 ance of the Aurora in the zenith. The *' dusky track," which 

 remains after the lights which have enlivened it are extinguished, 

 and in which they are so often seen again, may seem to attest 

 the justice of his opinion, that these appearances in the zenith 

 are no other than the far-projected tops of the columns which 

 have their bases in, or rather below, the horizon ; tops 

 which, while they fill the southern half of the zenith, to the 

 view of spectators under our parallel, must gradually descend 

 toward the horizon, in the eyes of such as behold them further 

 and still further to the south ; till, like the topmast of a re- 

 ceding ship, they first scarcely remain discoverable above the 

 convexity of the surface intervening, and finally dip and sink 

 beneath it. But, upon this assumption, the appearance, and 

 therefore office, of the Aurora Borealis, must be conceived as 

 extending far to the southward of even our own island ; and 

 the statement, as in the eleventh sentence, becomes more or 

 less inaccurate, that " only the extremities of these northern 

 phenomena" are witnessed by ourselves. In reality we are 



