94 The Rev. H. Lloyd on the Results of Observations made at the 



23. The preceding results are mdependent of the direction of the distur- 

 bance. If, however, we take the sum of the squares of the easterly and westerly 

 deviations separately, we find that the easterly disturbances preponderate during 

 the night, and the westerly during the day ; the former are, however, much 

 more considerable than the latter, and the difference reaches a maximum 

 about 10 P.M. 



Let 2 A/ denote the sum of the squares of the positive, or easterly distur- 

 bances, and 2A.- that of the negative, or westerly ; then the mean values of the 



♦ ~ " > are the following. The values in which the easterly 



function xj 



disturbances preponderate are distingxiished by the positive sign, and vice versa. 



Table XIV. Mean values of 



/( 



SA.2 - 2A_2 



)■ 



It thus appears that the mean disturbance observes a regular daily period, 

 both in magnitude and direction ; and this period, it is worthy of remark, is 

 precisely the reverse of that of the regular diurnal movement, — the mean posi- 

 tion of the magnet being nearly constant during the night, the mean disturbance 

 during the day ; — the principal oscillation of the magnet, in the regular move- 

 ment, being to the west during the day, while that of the irregular movement is 

 to the east during the night. 



24. From these remarkable relations it seems evident that the two classes 

 of phenomena are physically connected ; and I am inclmed to regard the dis- 

 turbance which prevails about 10 p. m., as an irregidar reaction from the regular 

 day movement, and dependent upon it both for its periodical character and 

 for its amount. 



If this hypothesis be a just one, it will, of course, follow that the magnitude 

 of the mean disturbance will vary in some direct proportion to the daily range, 

 and should, therefore, be greater in summer than in winter. This appears to 



