On Diurnal Variation of Barometric Preesure. ^'J 



The data used were the small chart giving the ^ lines of equal 

 annual temperature variation" in Berghaus' s Physikalisches Atlas, 

 III. Abt., Meteorologie, No. I., from which the mean annual 

 amplitude for the zone of latitude 20° — 60° N. for every ten degrees 

 of longitude was determined, from the mean values for the three 

 latitudes 20°, 40° and 60°N. at the corresponding longitudes. The 

 value a' thus obtained was plotted in a diagram with the longitude 

 X as abscissa and the resulting curve was smoothed down by taking 

 for each thé mean values of a"s at a; -20°, x- 10°, x, a;+10° and 



da' 

 a: + 20°. From the smoothed curve thus obtained, the value of -5— 



was determined for every ten degrees of longitude by drawing the 

 tangent at the corresponding point of the curve. The resulting 



da' 

 curve for --j— was again smoothed down in a similar manner and 



d^a' 

 then -j-ô- was determined^\ The values of the differential co- 

 dx" 



efficients were substituted for -^ — and -r-r in (10) and a?^ and 



^^ calculated for each 20° of longitude. The result is shown in the 

 following table and also plotted in Fig. 8. , in which the calculated 

 value proportional to a/ is given in an arbitrary scale. The agree- 

 ment of the calculated and observed curves are rather remarkable, 

 if we remember the nature of the assumptions made in the deriva- 

 tion of the formula (10). 



1) It may be remarked that the values of the differential coefficients thus obtained are 

 actually given by 



dx' 1 / \ 



d2ix' 1 / \ 



dx^ 4didj ^ ^ - 1 -' ' - 1 J ' 



as far as we consider the part of the curve to be smoothed may be regarded as linear within 

 the range 2fZi or 2^2- In our case 2di and 2i.j are equal to 50°. 



2) Of course we may obtain only the value proportional to ax. 



