of the North American Continent. 381 



Meteorological Reductions*, that they may be produced by 

 the crossing of two large atmospheric waves moving in differ- 

 ent directions. Some interesting evidence of the existence of 

 such atmospheric waves has been brought forward at late 

 Meetings of the British Association. This evidence rests 

 entirely on the barometric affections of the atmosphere over a 

 large tract of country. In order, therefore, to extend our 

 knowledge of the rotatory gale (Redfield) or the centripetal 

 hurricane (Espy), especially with regard to the desiderata 

 above-mentioned, I apprehend it will not only be important, 

 but absolutely necessary to accompany all the observations of 

 the direction, force, and variation of the wind with barome- 

 tric readings. These readings, however, must not be confined 

 to the mere period of the passing of the gale ; evidence has 

 been adduced of the passage of large atmospheric waves oc- 

 cupying from fifteen to seventeen days between the anterior 

 and posterior troughs, or between successive crests ; so that 

 in order to detect the origin of a gale arising from the intersec- 

 tion of two waves, to trace it throughout its destructive course 

 and to observe its final disappearance, it will be essential to 

 discuss the entire system of observations appertaining to both 

 waves, not only in time, but also in space. Our meteorolo- 

 gical observations are approaching a degree of uniformity and 

 system that bids fair for uniting these kindred inquiries. I 

 have now before me Prof. Loomis's interesting and ably con- 

 ceived charts for exhibiting the principal phaenomena during 

 the passage of two storms over the United States in February 



1842, in which he clearly shows the barometric, thermome- 

 tric, and anemonal phaenomena, and exhibits in a very stri- 

 king manner the extent of rain, snow, cloud, and blue sky 

 over the whole of the United States twice in the course of 

 each day that the storms prevailed. The barometric phaeno- 

 mena are shown by lines of equal pressure; and I apprehend 

 that these lines of equal pressure indicate, especially in one of 

 the two cases, that two waves passed over the United States; 

 that as the posterior slope of one wave passed off, the anterior 

 slope of a wave of a different system approached; and that in 

 the point of intersection the storm raged. Should the entire 

 barometric observations taken over the United States on that 

 occasion, February 1 to 4, 1842, support the theory of at- 

 mospheric waves, I apprehend Sir John Herschel's sugges- 

 tions will be partly realized. 



I cannot close this notice without adverting to a most 

 important desideratum in this interesting inquiry. Mr. Red- 



* Report of the British Association for the Advancement of Science, 



1843, p. 100. 



