628 



The westerly and easterly deflections in the British Islands, as 

 represented by the automatic records at Kew, are obviously governed, 

 as in all other parts of the globe where the phenomena have been 

 analysed, by distinct laws. The westerly deflections have their chief 

 prevalence from 5 A.M. to 5 P.M., or during the hours of the day ; 

 the easterly deflections, on the other hand, prevail chiefly during the 

 hours of the night, the ratios being above unity from 7 P.M. to 3 A.M., 

 and below unity at all other hours. The easterly have one decided 

 maximum, viz. at 11 P.M., towards which they steadily and con- 

 tinuously progress from 5 P.M., and from which they as steadily and 

 continuously recede until 5 A.M. the following morning. The 

 westerly deflections appear to have two epochs of maximum, one 

 from 6 to 7 A.M., the other about 3 P.M., progressing regularly 

 towards the first named from 3 A.M., and receding from it to 9 A.M. ; 

 at 9, 10, and 1 1 A.M. the ratios remain almost sensibly the same, but 

 towards noon they begin to increase afresh, and continue to do so 

 progressively to the second maximum at 3 P.M., from which hour 

 they progressively decrease to 7 P.M. Those ratios which are less 

 than unity, viz. those of the westerly deflections from 6 P.M. to 

 4 A.M., and of the easterly from 4 A.M. to 6 P.M., do not in either 

 case exhibit the same decided tendency to one or two well-marked 

 minima, as the ratios which are above unity do in both cases towards 

 their maxima. It is possible, however, that this may in some degree 

 be explained by the following consideration : 



The aggregate values of the disturbances prevailing at the different 

 hours, as stated in the Table, are those which have prevailed, not 

 only over the forces which would retain the magnet in its mean po- 

 sition, but also over any disturbing influences in an opposite direc- 

 tion, which may be conceived to have existed contemporaneously ; 

 and we cannot but suppose that as both westerly and easterly dis- 

 turbances do record themselves as prevailing at the same hours on 

 different days, that these opposite influences may sometimes coexist y 

 neutralizing each other and not appearing in the record. We may 

 reasonably suppose that the degree in which the aggregate values in 

 the Table, both westerly and easterly, may be diminished thereby at 

 the different hours, may be in some measure indicated by the dis- 

 parity, or the reverse, in the amount of the aggregate values of dis- 

 turbance in the opposite directions at those hours. Thus we may 



