150 On the Meteors of 13th November, 1833. 



tance towards the earth, according to the laws of falling bodies. The 

 atmosphere may either be considered as terminating at the height of 

 fifty milesj or as being, beyond that limit, so rare, as to afford no sensible 

 resistance to the descent of bodies ; for, at this elevation the air would 

 be nearly twenty times as rare as it can be made by the best air 

 pumps. The question before us then is, what velocity would a body 

 acquire in falling from a point 2238 miles above the earth, to within 

 fifty miles of its surfaced 



if a denote any distance from the center of the earth, and x a less 

 distance from the same center, r the radius of the earth, and m the 

 space passed through in 1" at the surface, then the velocity acquired 

 in falling through a — a? will be given by the following formula.* 



V ax 



m . . „ / 16.1X2188 \i . ., 



That is, V=7912^^g^ 6W ^^ miles. 



Hence it appears, that the meteors entered the earth's atmosphere 

 with a velocity more than ten times greater than the maximum velo- 

 city of a cannon ball, and about nineteen times that of sound. We 

 shall find reason to believe that these bodies were, in many instan- 

 ces, of great magnitude ; and the immediate consequence of the fall- 

 ing of a body with this prodigious velocity must be, a powerful con- 

 densation of the air before it, thus retarding its progress, and pro- 

 ducing also a great evolution of heat. 



We may call to mind here, what is known respecting the density of 

 the air at different elevations. At the height of seven miles above 

 the surface, the air becomes four times as rare as at the surface, and 

 this rarefaction increases in the same ratio as the height is increased, 

 according to the following law : 

 Heights, 7 14 21 28 35 42 49 



Densities. ^ - 1 — J 1 i \ -!-• r 



ASeil&lUCb, 4 ]6 ^^ -_~ JO 2 4 4 96 T6 3 84 



Hence, at the height of twenty one miles, the air is sixty four 

 times as rare as at the surface ; and at the height of forty nine miles, 

 16384 times as rare. It follows that three fifths of all the air contain- 

 ed in the atmosphere, is within four miles of the earth. 



* See Vince's Fluxions, Pr. XL. Ex. 5. Young's Mech. Art. 116. 



t It is worthy of remark, that the velocity of the Weston meteor, as estimated 

 by I>r. Bowditch, was three and a half miles per second. (Mem. Amer. Acad. 

 in. 134.) 



