172 THE CHEMISTRY OF CREATION. 



superior to that in which these properties are 

 possessed by our atmosphere, as the air tran- 

 scends quicksilver in the same properties. 



The condition of things on the surface of the 

 air is, allowing that it has bounds, one of a very 

 peculiar kind. At a certain limit the air is 

 supposed to have lost its elasticity ; and the 

 balance between the forces of elasticity and the 

 earth's attraction may be considered as the real 

 limit of the atmosphere. This equilibrium is 

 supposed, as has been stated, to have its situation 

 at a height of from forty-five to fifty miles. 



It is very certain that an extreme degree of 

 rarefaction may take place at an elevation up to 

 which it is quite within the power of man to 

 attain. Travellers on the high lands of South 

 America relate that they experienced the most 

 distressing symptoms in consequence of the 

 extreme tenuity of the air ; these were, great 

 difficulty of respiration, uneasy symptoms in 

 the head, and loss of 'muscular power. Mr. 

 Darwin informs us, that he himself experienced 

 this sensation, which is called by the natives, 

 the puna ; they recommend onions as a remedy, 

 perhaps with some benefit, as Dr. Pereira tells 

 us that raw onions are occasionally useful as an 

 expectorant. Strangers who come to reside in 

 some of the villages situated at the elevation 

 of from 10,000 to 12,000 feet above the level of 

 the sea, do not get over the sensation for almost 



