218 



PHILOSOPHY OF STORMS, 



NUMBER I. 



In order to make the general mass of our community acquainted 

 with Mr. Espy's theory, as explained by himself in two lectures deliv- 

 ered recently in our city, I propose to furnish a weekly communication, 

 until I have gone through with the information contained in those lec- 

 tures. In the course of my observations it may be possible that I may 

 misinterpret Mr. Espy, although I shall endeavor to confine myself 

 AvhoUy to those matters which I think I fully understand, interspersing 

 them, however, with such remarks and explanations as will bring the 

 subject down to the comprehension of all. 



Ever since the discovery of the barometer it has been known to 

 stand loio in the midst of storms^ and lower in proportion to their mag- 

 nitude. The barometer is nothing more than a glass tube, usually about 

 thirty-six inches long, hermetrically sealed at one end, then filled with 

 quicksilver, and its other open end inverted and immersed into a small 

 basin of the same metal in a perpendicular position. There is, there- 

 fore, a column of mercury within the tube communicating with a body 

 of mercury outside the tube, whose immersed end must be carefully re- 

 tained below the level of the surface so as to prevent the ingress of air 

 to its interior : just as in a common pump-stock in a well of water. 

 This little instrument is employed to determine the vveight of the at- 

 mosphere, and acts in the following manner : a column of atmospheric 

 air, whose ordinary height is supposed to be about forty-five miles 

 presses upon the surface of the metal in the basin outside the tube, and 

 counteracts the pressure of the column of quicksilver within the in- 

 verted tube, and prevents it from running out into the basin ; so that the 

 barometer acts precisely on the principle of the common balance. — 

 When the atmosphere is heaviest the column of mercury in the tube is 

 highest, and vice versa, its height being in exact proportion with the 

 weight of tlie superincumbent air. Now it has been ascertained by ex- 

 periment that at the level of the sea the pressure of the atmosphere is 

 capable of supporting a column of mercury of one inch square and 

 thirty inches high, and that this amount of mercury weighs fifteen 

 pounds. Hence a column of air, at this level, one inch square and ex- 

 tending to the extreme limit of the atmosphere, must also weigh fifteen 

 pounds. The barometer, however, does not always stand at thirty 

 inches, sometimes being higher, sometimes lower, indicating thus a va- 

 riation in the pressure of the atmosphere. Every inch of variation of 

 the instrument is equivalent to half a pound in weight in the pressure 

 of the air on every inch of surface. The average height of the barom- 



