LABORS OF THE JOINT COMMITTEE. 107 



south west, and blew hard all night, and till ten next morn- 

 ing. At Philadelphia it was very calm and foggy all the 

 evening, till about eleven, when the wind rose suddenly 

 and violently from the south west, and blew a hurricane 

 nearly all night, changing round to north west at four next 

 morning. It is worthy of particular remark, that at Flush- 

 ing the wind began to blow towards the point of greatest 

 rain about four hours sooner than it did at Philadelphia, 

 about one hundred miles more distant from the centre of 

 the storm. This is in remarkable accordance with the 

 fact detailed above, concerning the time the wind set in 

 at Philadelphia from the south east on the morning of the 

 20th June, towards a very great rain which had been going 

 on then for eleven or twelve hours at Silver Lake, and in 

 that vicinity. 



113. From all these facts, in connexion with those de- 

 tailed in our previous reports, it is, we think, abundantly 

 proved, that the air moves inwards towards the centre of 

 great rains, and consequently upward in the region of the 

 cloud. Nor is this inward motion difficult to account for. 

 It has been long known that the barometer stands low in 

 the middle of great storms, and nothing is more plain than 

 that the air will run on all sides towards the point where 

 the barometer stands lowest, with a velocity proportional 

 to the square root of the depression. And as this air mounts 

 upwards over the point where the barometer stands lowest, 

 a condensation of the vapor must take place from the cold 

 produced by diminishing pressure as it ascends. Now, the 

 chairman of this committee has shown by calculation from 

 acknowledged data, that for every pint of water which is 

 formed by condensation of vapor, the cloud itself is expand- 

 ed seven thousand six hundred pints by the latent caloric 

 given out at the moment of condensation. Thus will the 

 upward motion in the cloud be continued as long as air 

 highly charged with vapor runs in below. 



