Diurnal Variation of the Magnet at Kew. 



143 



corresponding Greenwich results, as published by the Royal 

 Observatory (see Table I.). Thus for the total range for each 

 year at Kew and Greenwich we have the following : — 



Total Ranges. 



Year. 



Kew. 



Greenwic h. 



1883 



9'-0 



7'-6 



7-'4 



8'-5 

 7'3 

 6'9 



1886 



1887 





It is noteworthy that the total range at Kew determined 

 from quiet days is greater than that at Greenwich determined 

 from all days except those of great disturbance. If we may 

 argue from* so small a comparison this indicates that storms 

 on the whole diminish instead of increasing the diurnal ex- 

 cursions of the needle. The total range is also apparently 

 decreasing yearly. 



The range of differences of the corresponding mean hourly 

 values is : — 





Range of Differences. 



Year. 



Greenwich and Kew ... 



-0'-7 to +0'-8 

 -l'l to +0'-7 

 -T-1 to +0'-8 



1883 

 1886 



1887 



There is thus in 1883 a difference of l'*5 in a range of 9' — 

 the percentage being 16*7. For 1886 the difference is l /# 8 

 in a range of 7'*6 — or 23*7 per cent. ; while for 1887 the 

 difference is l /# 9 in a range of 7 /# 4, or 25*7 per cent. 



Table II. shows the differences of the hourly readings for 

 the three years just determined, together with the dif- 

 ferences for the years 1870, 1871, and 1872, as determined by 

 Mr. Whipple (Rep. Brit. Assoc, loc. cit.). The mean of these 

 hourly differences for the six years has been taken (see 

 Table II.). It is noticeable that there is considerable uni- 

 formity in the nature of the differences between the mean 

 hourly readings for Greenwich and Kew respectively. Thus, 

 for each year, the Greenwich mean curve falls below that 

 obtained from the Kew magnetograph at about 7 p.m., and 



