A T M 



ATMOSPHERE. 

 Atmospheric air, properties of. 



1. Fluidity, elasticity, expansibility, and gravity. 

 Atmospheric air, composition of. 



2. Nitrogen 79 parts, oxygen 21, and about 1 part in 1000 of i-ari>onir 

 acid gas. It also contains about 1 per cent, of water in the state of ela<- 

 tic vapour. If the calculation be made by weight, there will be, in every 

 100 measures of atmospheric lair, 23 of oxygen, and 76- of nitrogen. 



Atmosplieric air, specific gravity of. 



3. Specific gravity of air I that of water '.'. 1 : 832 or 833, wlu?n redu- 

 ced to the pressure of 30 inches of the barometer, and the mean temper- 

 ature of 55. of the thermometer. 100 cubic inches of air at the surface 

 of the sea, when ihe thermometer is at 60, weigh 30 gram-;. 



Atmosplieric air, rarefaction and condensation of. 



4. The ratio of the spaces occupied by a given quantity of air in it? 

 greatest state of rarefaction, is to the same under the highest degree of 

 condensation, as 550.000 to 1. 



Atmosphere, weight or pressure of. 



5. The pressure of the atmosphere in its mean state is equal to a co- 

 lumn of quicksilver of an equal base and 30 inches high, or to a column 

 of water of 34 feet in height. Hence its weight on every square inch i* 

 nearly equal to lolbs. Mr Cotes computed that the pressure of this am- 

 bient fluid on the whole surface of the earth is equivalent to th;tt of a 

 globe of lead of 60 miles in diameter ; and admitting the surface of a 

 man's body to be about 15 square feet, he must sustain 32,100 Ibs, or near- 

 ly 14| tons weight. But since the variation in the height of the mercurial 

 column may occupy a range of 3 inches, every square inch base on any 

 body may at one time be pressed more than it is at others by a weight 

 equal to three cubic inches of mercury. Hence it may be easily shewn 

 that the difference in the weight of air, sustained by our bodies, in dif- 

 ferent states of the asmosphere, is often near a ton and a half. 



Atmosphere homogeneous, height of. 



G. Let H height of homogeneous atmosphere, % its uniform density, 

 b the height of the barometer in feet, and D the density of tht> mercury, 

 then 



At a medium 5 : D :: 1* ; 13600; and 6. it a mean SOinrlie? --4f<M'f, 



27318 feet, = raiii<-r m<,r. timi. ">; mite?, 

 i 



20 



91 y 13600 



,% H = ? ~^^ 



