74 Particulars respecting an irised Aurora Borealis. 



though as I have never happened to meet Avith a notice of the fact 

 by others, farther examination may be required. I should indeed 

 have felt some doubts of my own accuracy in the above account of 

 the Aurora Borealis, had I not at the time compared notes witli the 

 two gentlemen before mentioned. 



I have avoided inferences and deductions from the irised Aurora, 

 and the theories connected with polar ice, &c. If the fact does not 

 exhibit a new " decus coeli," it is probably rare in this region, and this 

 notice of it may lead to a more vigilant observation, should there be 

 a recurrence. 



In an examination of this sort, we have many known principles to 

 guide us : — The laws of the spectrum, the general laws of reflection 

 and refraction (which may give us the position of the reflection and re- 

 fraction of the original illuminator) are known and within the obser- 

 vation of every one, on the great scale, during the summer, and at 

 our great falls during most of the year ; while on the small scale, ev- 

 ery house supplies the means of experiment. Should these notes 

 (sent at your suggestion) lead only from a negative towards a positive, 

 from shewing what is not the source of the Aurora Borealis, towards 

 what is that source, they may not prove entirely without utility. 



Remarks. 



The colors usually mentioned as being exhibited by the northern 

 lights are white and yellow, and as they grow more active they usually 

 become red, increasing sometimes in intensity to blood red. Occa- 

 sionally, other colors are mentioned, as green, blue and purple.* In 

 an aurora which occurred Dec. 18th, 1736, at Oswer Zornea, Mau- 

 pertius observed that an extensive region of the heavens towards the 

 south appeared tinged of so lively a red that the whole constellation 

 Orion seemed as if dyed in blood. This light was for sometime fix- 

 ed, but soon became moveable : and after having successively assum- 

 ed all the tints of violet and blue, it formed a dome, of which the sum- 

 mit nearly approached the zenith in the south west. Its splendor was 

 so great, as to be in no degree affected by the strong light of the moon. 

 Maupertius adds that he observed only two of these red northern 

 lights in Lapland, which are of very rare occurrence in that country, 

 although the aurora there assumes a great variety of tints." For 



Musch, Institutes^ quoted by Edin, Encyc, 



