'26S METEOROLOGY. 



one ol' the contributors to its pages, that the obscuration of the sky du- 

 ring the Indian Summer, and at numerous other periods spread out ovei* 

 the wliole year, was caused by moisture in the state of a very thin cloud 

 resting on the earth, and not by real smoke agreeably to the prevailing 

 opinion. For this assertion numerous reasons were assigned, which, to 

 the writer, seemed satisfactory. 



The correctness of the views advanced by Iiim has, however, been 

 called in question by a correspondent from St. Louis, Mo., an officer in 

 the United States Atmy, antl resident for some tiinc on the western prai- 

 ries. Under dale of July 1st. 1816, he writes as follows: '' ! am deci- 

 dedly of the opinion that the snioiiy appearance is occasioned by the 

 burning of the prairies, which, you will recollect, embrace some thou- 

 sands of square miles in this western world. In the fall, through the 

 winter, (when the snow happens to be light,) and in the spring, fires are 

 raging on these immense tracts, which occasion a smoke so dense that 

 I have sometimes found myself unable to see two hundred yards so as 

 to distinguish an object as large as a house. This smoke, being carried 

 eastward, occasions that haze which, if it happen to coincide with a pe- 

 riod of calm weather, is called Indian Summer.'^'' 



Upon these statements, several remarks may be made, showing the 

 insufiiciency of his explanation of the phenomenon in question. 



1. As he does not dissent from the main point maintained in the 1st 

 Vol. of the Journal, viz : that the Indian Summer and. other seasons of 

 smoky weather occur during a comparatively quiet state oj the atmosphere^ 

 his theory can only apply when the existence of the fires on the prai- 

 ries, and this condition of the atmosphere " happen to coincide." But 

 the fires are evidently accidental and irregular, whilst the smokiness is 

 retrular, and always accompanies a comparative rest in the air for several 

 days together. The smoke from the burning of the prairies would pro- 

 duce obscurity in all conditions of the atmosphere, and could but add 

 intensity to the obscurity due to another course. It is readily granted 

 that extensive fires raging in the west at the time of the Indiam Summer 

 would distinguish it as eminently smoky. 



2. But his theory does not, by any means, explain that oft-recurring 

 phenomenon — a smokyskyimmediately after long-continued and drench- 

 ing rains over llie whole country, when nothing combustible remains in 

 prairie or forest. In June last, for example, near its close, and a few 

 days after the reception of his letter, the atmosphere was very smoky 

 for three or four days, notwithstanding that nearly the whole United 

 States territory had just been drenched with copious rains, and it would 

 have been next to uTipossible to kindle a lire on the prairies. The last 



