the Luminiferous ^Ether. 



407 



Height. 



Density or ten- 

 sion, that at the 

 earth being 

 unity. 



Number of 



molecules 



in a cubic foot. 



Length 



of the 



mean free 



path. 



Fractional 



parts of 



earth's radius. 



Approxi- 

 mate in 

 miles. 







tV 



1 



?9 







50 

 100 



1 



io- 4 ' 3 

 io- 8 ' 4 



25 



17x10 

 17x10 

 17xl0 16 ' 6 



2xl0- 6 inch 

 2X10- 1 ' 7 „ 

 2xl0 24 „ 



1 

 5" or 



200 



10 -16-4 



17xl0 8 ' 6 



792,000 miles 



T3- 



282 



io- 23 



17xl0 2 



31X10 11 „ 



1 



395 



io- 31 



17xl0" 6 



31xl0 19 „ 



1 



800 



10~ 57 



17xl0~ 32 



31xl0 45 „ 



1 



3956 



io- 172 



17xl0" 147 



31xl0 160 „ 



2 



7912 



IO" 230 



17xl0- 2 °5 



31X10 218 „ 



00 



00 



10 -345 



17X10-320 



31x10^3 M 



The numbers in the third column multiplied by ^ will 

 give the density (or mass per cubic foot) at the respective 

 altitudes ; and the same numbers multiplied by 15 (or more 

 accurately 14*7) will give the tension per square inch. Ac- 

 cording to this law, at an elevation of 300 miles the density 

 of the atmosphere will be somewhat less than the density of 

 the aether as given by equation (9). 



To find the height at which the tension of the atmosphere, 

 according to the above law, will be the same as that of the 

 sether, we have, by means of equations (11) and (25), sub- 

 stituting in the latter 2116 for ^- , 



r* 4 



2116x10-^+*=^, 



10* 



which solved gives 



: 3F24 ===126,6 mileS ' 



so that at the height of 127 miles the tension would be less 

 than that of the sether, the temperature being uniform. 



The mean free path according to the above law, in which 

 gravity varies as the inverse squares, is less, and for great 

 heights much less, than would be found according to the 

 ordinary exponential law. Thus Crookes states that the mean 

 free path of a molecule at the height of 200 miles is about 



2G2 



