198 



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 lift- 

 ing up of warm air into regions about the earth's surface, by its dis- 

 placement by a cold current originally above it, and from an oppo- 

 site 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 considerable 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 phenomena. 



The author then explains the causes of the observed rise of the 

 thermometer to be due to the warm south-east wind, and the subse- 

 quent depression to the cold north-west wind. 



The author next examines the causes which have been assigned 

 for the fluctuations of the barometer during this storm, selecting, as 

 applicable to the present case, the following: — "The south-east wind, 

 which accompanied the rain, moved with an accelerated velocity. 

 The particles, therefore, of air, at one extremity of the current, must 

 have left those of the other extremity at an increased distance. 

 Hence a mechanical rarefaction, and, of course, diminished pressure. 

 The reverse effect must have taken place after the storm had passed.. 

 A north-west wind sets in with great violence. A vast body of air 

 is precipitated toward the south-east. The partial vacuum which at 

 first existed, is very soon supplied : yet, though the first impelling 

 cause has ceased to act, the momentum of the excited current still 

 urges it onward, and a condensation results, which continues the rise 

 of the barometer." 



The author concludes by remarking, that he has availed himself 

 in these discussions of the suggestions of writers on meteorology, and 

 is especially indebted to the labours of Messrs. Redfield, Espy, and 

 Reid. 



Dr. Hare read a communication entitled "Engraving and 

 description of an apparatus and process for the rapid congela- 

 tion of water, by the explosive evolution of ethereal vapour, 

 consequent to the combined influence of rarefaction and the 

 absorbing power of sulphuric acid, by Robert Hare, M. D.," 

 which was referred to a Committee. 



