36 Proceedings of the American Philosophical Society. 



discussion of its peculiarities, that it was not — the progress of the baro- 

 metric minimum in Europe being from north to south, inclining a little to 

 the west. 



The author next proceeds to generalize the deductions in regard to the 

 circumstances of this storm, and to apply them as tests to the different 

 theories of wind, rain, dz>c. 



He first endeavors to show how far registered observations of the wind 

 may be influenced by localities, and their accuracy affected by the mode 

 of observing, and the transcribing of the registers; and concludes that it 

 is indispensable to regard the average of directions at near stations, and 

 not those at individual ones, and gives some examples of discrepancies at 

 places near each other in support of this opinion. The anomalies pre- 

 sented by the stations in the State of New York are very curious. 



The causes assigned by theory for the production of winds are next 

 enumerated and discussed. Recurring to the observations, the author 

 traces a connection between the direction of the surface wind on the 18th 

 and 19th of December, and a maximum of the barometer existing on a 

 line nearly north and south, moving eastwardly, and passing on the morn- 

 ing of the 20th of December nearly through the eastern extremity of the 

 State of Maine. At this period a minimum of the barometer existed 

 nearly on the line of the river Mississippi, and the winds blew towards 

 this line. This minimum is traced in its motion eastward ; and in con- 

 nection with it, the change of wind from the easterly to the westerly 

 quarter. On the afternoon of the 21st, the line of minimum pressure 

 had reached Boston ; and on the 22d, the northwesterly wind now pre- 

 vailed at nearly all the stations. The direction and approximate force of 

 the wind on the morning of the 2lst, are represented upon a map of the 

 United States, accompanying the memoir. From an examination of a 

 phenomenon of the wind. Prof Loomis concludes that the southeasterly 

 current rose, so that the northwesterly wind thus became the lowermost 

 current ; and subsequently, from an examination of the phenomenon of 

 the rain, snow and hail, that the rising current was, in part at least, de- 

 flected back upon itself The immediate cause of the soutlieasterly wind 

 is traced to the existence of a minimum of pressure at some point north 

 of the United States. 



The author next examines the various causes which have been, or may 

 be, in his opinion, assigned as producing rain, and infers that the most 

 common cause of rain, in these latitudes, is the sudden lifting up of 

 warm air into regions about the earth's surface, by its displacement by 

 a cold current originally above it, and from an opposite direction ; and 

 that such was the actual cause of the rain in question, a warm current 

 from the south having been displaced, and caused to rise to a considera- 

 ble elevation by a cold current from the west. The mixture of the warm 

 and cold air is inadequate, in the author's opinion, to account for the phe- 

 nomena. 



