ISC 



PNEUMATICS. 



becoming, however, rarer, in proportion to its dis- 

 tance from the earth. 



It is observed, that at a greater height than 45 

 miles, it does not refract the rays of light from the 

 sun; and this is usually considered as the limit of 

 the atmosphere. In a rarer state, however, it may 

 extend much farther. And this is by some thought 

 to be the case, from the appearance of certain me- 

 teors which have been reckoned to be 70 or 80 

 miles distant, and whose light is thought to depend 

 upon their coming through our atmosphere. 



Dr. Cotes has demonstrated that, if altitudes in 

 the air be taken in arithmetical proportion, the 

 rarity of the air will be in geometrical proportion. 

 For instance, 



. 



4^ 



16 



64 



256 



1024 



4096 



16384 



655S6 



262144 



1048576 



, 4194304 



... 16777216 



67108864 



268435456 



1073741824 



4294967296 



17179869184 



68719476736 



274877906944 



1099511627776 



by 



V 



And hence it is easy to prove by calculation, that 

 a cubic inch of such air as w r e breathe would be so 



