458 MATHEMATICS AND NATURAL PHILOSOPHY. 



Trans, for 1S56, Art. XV. By a process of this description, the disturbances of 

 principal magnitude in each of the three elements, the Declination, Inclination and 

 Total Poree, have been separated from the other observations, at the three Obser- 

 vatories of Toronto, Hobarton, and St. Helena, and submitted to an analysis of 

 ■which the full particulars -will be found in the preliminary portions of the volumes 

 ■which record the observations. By the adoption of a uniform magnitude as con* 

 stituting a disturbance throughout the -whole period comprised by the analysis, the 

 amount of disturbance in the several years, months, and hours, is rendered inter* 

 comparable. The result of this investigation (which Could not be otherwise than 

 a very laborious operation, since the observations at a single one of these station?, 

 Toronto, considerably exceeded 100,000 in number, each of which had to be" 

 passed through several distinct processes,) has made known to us that the pheno-> 

 tnena of this class, which may in future with propriety aud advantage receive the; 

 appellation of " occasional? are, in their mean or average effects, subject to periodi- 

 cal laws of a very systematic character •, placing them, aa a first step towards atf 

 acquaintance with their physical causes, in immediate connexion with the sun aS 

 their primary exciting cause. They have — 1, a diurnal variation which follows 

 the order of the solar hours, and manifests therefore its relation to the sun's posi- 

 tion as affected by the earth's rotation on its axis ; 52, an annual variation, con- 

 necting itself with the sun's position in regard to the ecliptic ; and 3, a third varia* 

 tion, which seems to refer still more distinctly to the direct action of the sur^ 

 since, both in period and in epochs of maximum and minimum, it coincides with 

 the remarkable solar period of about ten, or perhaps more nearly eleven, of our 

 years, the existence of which period has been recently made known to us by the 

 phenomena of the solar spots ; but which, as far as we yet know, is wholly uncon- 

 nected with any thermic or physical variation of any description (except magnetic) 

 at the surface of the earth, and equally so with any other cosmical phenomena 

 with which we are acquainted. The discovery of a connexion of this remarka- 

 ble description, giving apparently to magnetism a much higher position in the 

 scale of distinct natural forces than was previously assigned to it, may justly be 

 claimed on the part of the Colonial Observatories, as the result of the system of 

 observation enjoined (and so patiently and carefully maintained), and of the in- 

 vestigation for which it has supplied the data ; since it was by means of the dis- 

 turbance-variations so determined, that the coincidence between the phenomena 

 of the solar spots and the magnitude and frequency of magnetic disturbances was 

 first perceived and announced (Phil. Trans. 1852, Art. VIII.) 



The extent and mutual relation of the disturbance-variations of the three 

 elements, even at a single station, supply a variety of points of approximation 

 end of difference, which are well suited to elucidate the physical causes of these 

 remarkable phenomena ; but valuable as such aids may be when obtained for a 

 eingle station, their value is greatly augmented when we are enabled to compare 

 and combine the analogous phenomena, as they present themselves at different 

 points of the, earth's surface. To give but a single example : — there are certain 

 variations produced by the mean effects of the disturbances which attain their 

 maximum at Toronto during the hours of the night ; the corresponding variations 

 attain their maximum, at Hobarton, also during the hours of the night, but with a 

 small systematic difference as to the precise hour, and with this distinguishing 

 peculiarity, that the deflection at Hobarton is of the opposite pole of the needle 

 (or of the same pole in the opposite direction,) to the Toronto disturbance ; whilst 



