FOR HIGH LEVELS IN THE EARTH's ATMOSPHERE. 83 



but 



hence 



In an analogous way, 



(Pr„-;>r,)„ = (nR)„ 



Then by substitutions in (30) we have 



^ = {^^X-(^rX (31) 



The number of moment-solenoids, A, has therefore the same dimensions as a pres- 

 sure, i. e., 



mass 



length, time^ 



or its equivalent, 



, . length' 



density x — -. s- . 

 •' time'' 



If the specific gravity, p^, of water at its maximum density be selected as our 



unit of density, then 



mile^ 

 a pressure of 1 inch of the mercurial column = 16.945 X p^ X ^ ^. 



If w^e choose the density of air, pi, at 32° F. and 1 atmosphere of pressure as the 

 unit of density, then 



mile^ 

 a pressure of 1 inch of the mercurial column = 13 105 X pj X = -^. 



Finally if p, = 0.169 45 p^ be chosen as unit of density, then 



mile^ 

 a pressure of 1 inch of the mercurial column = 100 X p., X , ^. 

 ^ '^- hour 



Therefore a closed curve composed of two verticals aa and hh, and two lines, 

 ah and ah lying in the level surfaces V= Vq and V= Vi respectively, for which curve 

 we have J^= (nS';)„ — (n {■■)(,= 1 inch of the mercurial barometer column, embraces 



16.945 moment-solenoids of the po ■ -, ^-system of dimensions ; or 13 105 moment- 

 solenoids of the pi • :j IT -system, or 100 moment-solenoids of the p^ • r 2 -system. 



On the nj'j-chart, see pages 67, 69, Figs. 4, 5, 9, curves for each 0.01 inch difference 

 of pressure have been drawn. Therefore each of the tubular figures in the atmos- 



