of the United States. 201 



of co-operative labour which distinguishes the present time, 

 we have every prospect of seeing this path successfully pur- 

 sued. Although the memoir itself is not very long, the illus- 

 trations which accompany it are many, and its republication 

 in this country without them would not convey the full amount 

 of instruction to be derived from the text and plates conjointly. 

 Memoirs of this description scarcely admit of an abstract; 

 there are however certain circumstances which present them- 

 selves in so striking a manner as common to the three storms 

 above mentioned, as to induce the belief that they may be 

 viewed as the characteristics of a particular class of storms 

 which occur in the United States in the winter months of 

 every year. The circumstances alluded to may admit of a 

 brief notice in the light of a first generalization ; and it may 

 have the additional advantage of attracting the attention of 

 some of your readers to the original memoir in the Transac- 

 tions of the American Philosophical Society. 



We may picture to ourselves, in the first instance, a nor- 

 mal state of the atmosphere over the United States, in the 

 departure from which we may trace the successive phases of 

 derangement which constitute the storm. In this normal 

 state the wind is from the west, or a few degrees south of 

 west, in the lower as well as in the upper current, with the 

 thermometer and barometer at or near their respective mean 

 heights for the time and place : the whole body of the air 

 from the surface of the earth to its upper limit, is proceeding 

 harmoniously in the one direction, and having blown across 

 the greater part of the continent of America before it reaches 

 the middle states of the union, it is extremely dry, and the at- 

 mosphere perfectly clear. 



The interruption to this normal state, which in the order 

 of time appears first to present itself, is a change in the direc- 

 tion of the lower stratum of the air, which becomes southerly 

 in the countries situated in the north of the Gulf of Mexico, 

 and south-easterly in the south-eastern states. The change 

 in the direction of the lower stratum of air is speedily followed, 

 or perhaps it should rather be said is accompanied, by cloud, 

 and by a rise of temperature, which progressively increase, 

 the one in extent and the other in intensity, attended by a 

 falling barometer. The cloud condenses into rain or snow, 

 the area of which progressively extends till but a compara- 

 tively small margin of cloud remains without precipitation. 

 The thermometer continues to rise, the barometer to fall, and 

 the rain or snow to descend, until the instant when the ab- 

 normal winds from the south and east give place to a more 

 violent rush of air from the west and north-west, by which 



