550 



Mr. A. B. McLeod 



2. Empirical Formulce for Density and Refractive Index. 



From the curve which accompanies the ' Computer's 

 Handbook' (Meteorological Publication, M.O. 223 4/18) 

 we have the values for the mean atmospheric density at 

 various heights, which are given in the second column 

 of Table I. These values are presumably for heights above 

 sea-level. The densities are in grams per c.c. and the heights 

 in kilometres. 



Table I. . 



h. 



km 



a (observed). 

 •001250 g. c.c. 



a (calculated) 

 •001250 g./c.c. 



1 , 



•001126 .. 



•001136 „ 



2 „ 



•001020 „ 



001029 „ 



3 „ 



000907 ., 



•000928 „ 



4 „ 



•000820 ,. 



000833 ,, 



5 „ 



•000739 ., 



•000743 „ 



6 



•000661 „ 



000661 





•000591 .. 



000584 ., 



8 „ 



•000525 „ 



000514 ,, 



9 ., 



•000466 „ 



000449 ., 



10 ., 



•000410 ,. 



.000391 ., 



11 „ 



•000356 ,. 



000339 „ 



12 ., 



•000301 



000293 ,, 



13 , 



■000261 ., 



0CO253 „ 



14 „ 



15 ., 



•000220 „ 

 •000191 ,, 



000219 : , 

 000191 .. 



The values in the third column of the table have been 

 calculated from the empirical expression 



a = -001250- •0001165/* + -000003063A 2 . . (16) 



The constants of (16) have been determined from the 

 observed mean densities at the heights 0, 6, and 15 km. 



It would have been rather better, as far as ordinary 

 aeroplane or airship observations are concerned, to have 

 taken the observed values at say 0, 4, and 8 km. But the 

 former values were selected as having a greater range of 

 usefulness for meteorological work. 



To determine the constant /x in (13) we have, for a wave- 

 length \==5000 A.U., at 0° C. and 76 cm. of mercury, 



^ 



■0002936 

 •00 L 293 



•2271 



