130 



It was a remarkable faet, he said, in the history of science, that no 

 one had adverted to a deduction from the Jaws of dynamics, which 

 he deemed incontrovertible, that the wind must blow inwards on all 

 sides of a storm, since the barometer is known always to stand low 

 at the centre, sometimes more than two inches lower than the mean: 

 • and he went on to show that, in narrow spouts or tornadoes, where 

 the friction of the air at the surface of the earth may be neglected, the 

 air, following the law of spouting fluids, would spout upwards with a 

 velocity of 240 feet per second, if the barometer should fall only one 

 inch ; and so in proportion to the square root of the fall. 



Mr. Espy stated that experiments had been made, both in Great 

 Britain and France, on dry air, similar to those which he had made 

 with his nephelescope ; but none, he believed, had ever been made 

 with moist air, so as to compare the results together. 



Finally, Mr. Espy gave a brief summary of the principles of his 

 theory. When the air becomes heated or highly charged with vapour 

 at the surface of the earth, it becomes lighter, and ascends in columns, 

 comes under less pressure, expands, becomes colder by expansion, 

 begins to condense its vapour into water or cloud, when it becomes 

 as cold as the dew point ; which it will do when it rises as many hun- 

 dred yards as the dew point is below the temperature of the air in de- 

 grees of Fahr.; and the higher it goes the more vapour will it con- 

 dense, the more latent heat will it give out, and the more will the 

 cloud expand by the latent heat evolved. The more also will the ba- 

 rometer fall under the cloud: this will cause the air to rush towards 

 the centre of the ascending column, where the barometer stands low: 

 the air thus rushing in will ascend and form cloud as before, and 

 thus the process will be continued as long as air continues to come 

 in, highly charged with vapour. And as the storm-cloud moves over 

 the surface of the earth, the air around is thus pressed in towards the 

 centre of the region under the cloud, and upwards into the cload, in 

 consequence of the diminished specific gravity of the air. 



The Committee of Finance presented the Treasurer's ac- 

 counts, with their annual report thereon; and the appropri- 

 ations for the service of the coming year were made, in accord- 

 ance with the recommendation of the Committee. 



On motion of Dr. Patterson, additional authority was confer- 

 red on the Committee appointed on the 9th of August last, 

 to make leases, &c. of the Museum Building. 



