32 



the two stations, are noticed as corroborating the conclusions, de- 

 rived from former investigations, of the character of these disturb- 

 ances as affecting contemporaneously the most distant parts of the 

 globe. 



Several tables are given containing the distribution of the sepa- 

 rated observations, — 1st, into the several ynontlis^ and 2nd, into the 

 several hours, of their occurrence, the hours being those of local 

 time. This is done, first, in regard to the numher of disturbed ob- 

 servations in the several months and hours; a separate account being 

 taken of those which are easterly, and of those which are westerly 

 deflections; and second, in regard to the mean numerical values of 

 the deflections at the different hours, distinguishing easterly and 

 westerly, and taken on a daily average throughout the year. The 

 results of this analysis are carefully stated ; and are conclusive, in 

 the author's opinion, in manifesting the existence of periodical laws 

 in the times of occurrence and in the effects of the larger disturb- 

 ances ; these lav/s having points of remarkable analogy at both 

 stations, and showing a causal connexion to subsist between the 

 disturbances on the one hand, and the seasons of the year and hours 

 of the day on the other. 



The author remarks on the practical bearing which the establish- 

 ment of such laws must have on the researches, which have been 

 recently brought before the Royal Society by one of its most distin- 

 guished members, into the physical causes of the periodical varia- 

 tions of terrestrial magnetism, particularly of the diurnal magnetic 

 variation. The present investigation shows that the latter pheno- 

 menon must now be regarded as consisting of two periodical varia- 

 tions, superimposed upon each other, having extremely dissimilar 

 laws, and probably therefore different immediate causes. These 

 constituent parts of the variation will bear different proportions to 

 each other in different parts of the globe, and in many parts of the 

 globe it will be necessary, in the author's opinion, to separate the 

 whole diurnal variation into its constituents in order to study their 

 respective physical causes. At Toronto and Hobarton the diurnal 

 variation occasioned by the disturbances forms a clearly recognizable 

 part of the whole diurnal variation ; the greater part, if not the 

 whole of that remarkable phenomenon, which Mr. Faraday has 

 termed the "nocturnal episode," appearing to be attributable to this 

 cause. 



The author concludes by remarking, that the investigation which 

 forms the subject of this paper cannot be regarded as complete, until 

 the influence of the larger disturbances on the phenomena of the 

 magnetic inclination and force have undergone a similar examina- 

 tion. This he hopes to have a future opportunity of submitting to 

 the Society. 



