AND EXTERNAL RESISTANCE. 317 



earth was estimated at 100 miles ; and whose 

 velocity was not less than 1000 miles in a mi- 

 nute of time. The indefinite elevation to which 

 the atmosphere extends, is more especially 

 proved by comets, by those meteors which 

 surpass every other of which we have any 

 knowledge, in magnitude and motion, as well 

 as in brilliancy and transparency, the sun alone 

 excepted. Instead of being rounded, like com- 

 mon meteors, they are, for the most part, dis- 

 tinguished from all other bodies, by having a 

 large mass of matter attached to them, in con- 

 sistency so semitransparent, that the smallest 

 star can be distinguished through it, in color 

 smoky, or clouded, and in figure striated and 

 fibriated like hair ; it is from this peculiarity in 

 the appearance of this portion of the whole, 

 that the name of Comet has been derived, from 

 Coma-Hair. 



When we reflect on the facts which I have 

 detailed, of the wonderful power of expanding 

 which air possesses, when external resistance is 

 weakened ; and more especially if the supposi- 

 tion entertained by Sir I. NEWTON be true, that 

 a cubit foot of air, carried to the elevation of 

 one semidiameter from the surface of the earth, 

 would expand as far as the orb of the planet 

 Saturn, we are bound to believe, that the cal- 

 culations which have hitherto been made, and 

 which confine the elevation of the atmosphere 



