Essay on the Indian Summer. 141 



Having stated that the Indian summer appears usually in the month 

 of November, we do not however, wish to be understood, that a ha- 

 ziness or obscurity of the air occurs in that month only, and that its 

 duration is confined, and peculiar to, a few days in the latter part of 

 the autumnal season — on the contrary, common observation (as well 

 as minute reference to meterological tables) proves, that it is by no 

 means uncommon in the month of October, and is frequently mistak- 

 en then for the true Indian summer, by persons unacquainted with 

 the proper period of its accession. This is a fact which we wish 

 borne in mind, — as it enables us to account for one of the general 

 laws, on which the phenomenon is dependant, but which would not 

 apply, were we erroneously to confine the prevalence of a hazy at- 

 mosphere, to a few days at the commencement of winter. — It is true 

 that at this period, there is usually a longer and more closely con- 

 nected exhibition of character, and to which (as before observed) 

 the term Indian summer is correctly applied — but were we to see no 

 analogy in the general aspect of the fall season, we should be forced 

 to search wholly among local causes, for the explanation of a fact, in 

 which a regular and extended variation of temperature, (dependent 

 on the sun's annual declination) is obviously concerned as a leading 

 or predisposing cause. 



The regular yearly changes of temperature greatly affect the trans- 

 parency of the atmosphere, and give it, at certain seasons, a peculiar 

 appearance ; for instance, during the spring, when the temperature of 

 the air is evidently on the increase, its capacity for moisture increases 

 faster than the additions which are made to its humidity by evapora- 

 tion or moderately moist winds ; whereas, during the autumn, the 

 temperature is as rapidly on the decline, and the capacity of the air 

 to contain moisture being on the decrease, a slight addition to its hu- 

 midity produces hazy or foggy weather. This autumnal obscurity of 

 the atmosphere would prevail more generally here (as it does in Eng- 

 land and the northern shores of Europe) were it not for the frequen- 

 cy of our north westerly winds, which from their dryness are always 

 attended with a cloudless sky. Having ascertained that the annual 

 variation of temperature is one of the great predisposing causes of 

 the phenomenon before us, we shall proceed to trace out other aux- 

 iliary causes. A second prominent cause, which we therefore 

 notice, is the prevalence of peculiar winds ; for the translations of 

 large portions of the atmosphere from one parallel to another must 



