seen in London, September 25, 1827. 409 



Aurora could not have been seen if the sky had not been more 

 or less clear. But the sky was very clear ; and this because the 

 weather was severely frosty . The thermometer " was standing 

 at the freezing point." The weather was settled frosty, and 

 therefore settled clear ; for the Aurora appeared for *' several 

 following nights." The atmosphere, therefore, was clear ; there 

 was neither cloud nor fog, and thence the whiteness of the 

 Aurora. But these views of the Aurora Australis were partial 

 occurrences, and were characterised, as we must conclude, by 

 the state of the atmosphere at a particular conjuncture, or at a 

 particular season of the year. In point of fact, the Aurora was 

 seen on the IGth of February, 1773, in latitude 58° S. This 

 w^as the beginning of the Australian winter, and it might be a 

 very cold, and therefore a very clear beginning. But the at- 

 mosphere of the southern half of the globe is not always thus 

 translucent ; and when it is otherwise, we may depend upon it 

 that the columns of its Aurora *' assume various colours,' espe- 

 cially those of a fiery and purple hue," more or less like our own. 

 A friend of the present writer was in the same latitude (58° 12' 

 S.) in the month of March, a few years since; and, upon 

 asking that gentleman whether he had ever beheld an Aurora 

 in the Southern Hemisphere, his answer was in the negative. 

 The season of his visit, however, was a month later in the 

 southern winter than the visit of Messrs. Cook and Forster ; the 

 weather Avas thick and sleety ; it was unfavourable to any view 

 of an Aurora at all ; but, had the phenomenon happened to 

 present itself, its appearance, we may believe, would not have 

 presented that of a uniform, clear, white light. 



4. In the fourth and sixth sentences, what is said of " change 

 of shape," and " change of form," is of a nature exceedingly to 

 mislead such as, never having themselves witnessed the phe- 

 nomenon, may desire either to figure it to their imagination, or 

 to reason upon its appearances. In reality, there is no such 

 change of shape or form as the words naturally suggest to 

 our ideas; the forms, under all changes, are still linear; and 

 the actual changes, as to form, are limited to such changes only 

 as can be produced with the single material of lines, lengthened, 

 shortened, varied in their direction, and now fixed, now shaken, 

 now darting; and now joined in rapid and intermingling motion. 



