1859] WRITINGS OF JOSEPH HENRY. 439 



those which enter our territory from the north at the eastern 

 base of the Rocky Mountains. Those of the first class, which 

 have been studied with much success by the lamented Red- 

 field and others, follow the general direction of the Gulf 

 Stream, and overlapping the eastern portion of the United 

 States, give rise to those violent commotions of the atmos- 

 phere which are in many instances so destructive to life and 

 property along our eastern coast. These storms from the 

 south are frequently two or three days in traversing the dis- 

 tance from Key West to Cape Race, and their approach and 

 progress might generally be announced by telegraph in time 

 to guard against their disastrous effects. Though the gen- 

 eral direction of these storms appears to be made out with 

 considerable certainty, much remains to be done in settling 

 the theory of their character and formation. 



The materials which have been collected at the Smithson- 

 ian Institution during the last seven years relative to the 

 other class of storms have enabled us to establish general 

 facts of much value, not only in a scientific point of view, 

 but also in their application to the prediction of the weather. 

 [This statement was verified by a series of maps, exhibited 

 to the Academy by Professor Henry, on which were indi- 

 cated the beginning and progress of some remarkable changes 

 of weather.] From these maps it appears that the great 

 disturbances of the atmosphere which spread over the sur- 

 face of the United States enter our territory from the posses- 

 sions of the Northwest or Hudson's Bay Company, about 

 the sources of the Saskatchewan, at the base of the Rocky 

 Mountains, and are thence propagated south and east, until 

 in many instances they spread over the whole of the United 

 States and probably a large portion of the British posses- 

 sions. 



For example, the great depression of temperature wliich 

 occurred in January of the present year, and wliich will be 

 remembered b}' every one as the most marked cold period 

 of the season, entered the territory of the United States at 

 the point before mentioned on the 5th of January, and on 

 the 6th reached Utah, on the 7th Santa Fe, and on the 8th the 



