GRAl'HS ON "QUIET" DAYS DURING THE TWELVE YEARS 1891 TO 1902. .587 

 TABLE IX. Monthly Relative Values, 1891 to 1902 (100 = mean from 12 months). 



Vector Diagrams. 



11. The mode ot variation throughout the year in the diurnal inequality of the 

 magnetic forces in the horizontal plane is conveniently illustrated by vector diagrams 

 ((A), 29). The accompanying diagrams refer to the mean monthly diurnal 

 inequalities for Kew (1890 to 1900) and Falmouth (1891 to 1902), thick lines lor the 

 former, thin lines for the latter. 



NS and EW represent respectively the geographical north -south and east-west 

 directions. Their intersection (thick lines for Kew, thin for Falmouth) answers to the 

 origin. The crosses and the numbers represent hours counted from midnight as 0, 

 the line from the origin to any number or cross representing in magnitude and 

 direction the disturbing force to which the diurnal inequality may be ascribed. The 

 line drawn from M to the corresponding origin marks the direction of the magnetic 

 meridian. For the periods considered the mean values of the declination at Kew 

 and Falmouth were respectively 17 18''8 and 18 47''4. The distances of the points 

 marked N, E, S, W from their corresponding origin represent in all cases lOy. Except 

 in the case of December and January the distance between the origins for Kew and 

 Falmouth would represent 5y. 



The hours are G.M.T., so that 12, for instance, on a Falmouth curve answers to 

 llh. 39'7m. A.M. local mean time, but on a Kew curve to llh. 5875m. A.M. local 

 mean time. If local time had been used, corresponding Kew and Falmouth radii 

 would have shown an even closer approach to parallelism than they do. 



3 D 2 



