A D. Bache on the Horizontal Component of Magnetic Force. 271 



T. 



bleXV 



-Diurnal 



isturbance v 



ariation 







.d. 



.1:o^:l1 





B.d. 



i"o.;t:crfa 



oh midnight, 



06 



000024 

 ?3 



li 



28 



ooo| 

 f 



The average amount bj which the disturbances tend to de- 

 crease the diurnal variation of the horizontal force is 14 scale 

 divisions or 0-00021 in the absolute scale. The maximum ef- 

 fect takes place at 8 P. M., at exactly the same hour when the 

 declination disturbances reach their greatest effect. 



In the preceding tables, Nos. XIII, XIV and XY, to the 

 hours indicated, 21^ minutes should be added, the observations 

 ^ing made so much later than the even hours. The preceding 

 discussion shows that for two stations, even at a comparatively 

 short distance, as for Philadelphia and Toronto, there are gener- 

 ally speaking some close coincidences in the laws derived from 

 independent observations ; but there are also certain differences 

 in other results ; yet it must not be forgotten that for a strict 

 comparability we require, if not simultaneous observations, at 

 least observations extending over similar parts or the whole of 

 an eleven year period. The Philadelphia series includes a min- 

 imum year of that inequality with the greater extent of observa- 

 tions before that epoch, whereas at Toronto the series begms &i- 

 tsr the minimum epoch, and barely ex.tends to a maximum 

 .year. ^ 



of the absolute 



aSd^for 



above, 8ho%ring the distribntion of t 



r„.ca,e"r 



;;r:l.or.,.. 



aSa-e:!. 



8 to 16 



io " 48 

 48 '• 56 

 56 " 64 



1 08 '1 i4-4 



|:| 



390 " 32-6 



'\ 



