406 



most mysterious change, by which the magnetic condition of the 

 globe at one epoch passes progressively and systematically into that 

 of another. It is specially by determinations of this class, obtained 

 with the necessary precision in different parts of the globe, that, in 

 the words of the Committee's Report, " the patient inductive inquirer 

 must seek to ascend to the general laws of the earth's magnetism." 

 At the time when the Report of the Committee of Physics was 

 written, doubts were reasonably entertained, whether the limited 

 time, during which the Colonial Observatories were likely to be 

 maintained in action, would be sufficient for the determination of 

 the secular changes ; and it was therefore very properly argued, that 

 " these changes cannot be concluded from comparatively short series 

 of observations without giving to the observations extreme nicety, so 

 as to determine with perfect precision the mean state of the elements 

 at the two extremes of the period embraced." It is with much 

 satisfaction, and with a well-deserved recognition of the pains which 

 have been bestowed by the successive Directors of the Toronto Ob- 

 servatory, and their Assistants, on this branch of their duties, that I 

 am able to refer to the determinations of the absolute values and 

 secular changes of the three elements contained in the third volume 

 of the Toronto Observations, in evidence that the instrumental means 

 which were devised, and the methods which have been adopted, have 

 proved, under all the disadvantages of a first essay, sufficient to de- 

 termine these data with a precision which is greatly in advance of 

 preceding experience, and, as far as may be judged, equal to the 

 present requirements of theoretical investigation. This is the more 

 deserving of notice, because Toronto is a station where the casual and 

 periodical variations, which it was apprehended would seriously in- 

 terfere with the determination of absolute values, are unusually large. 

 We may derive, therefore, from the results thus obtained, the greatest 

 encouragement to persevere in a line of research which is no longer 

 one of doubtful experiment, and to give it that further extension 

 which the interests of science require. 



Amongst the results which have recompensed the labours of the 

 Colonial Observatories in this branch of their inquiries, perhaps there 

 is none of more importance in respect to the general theory of ter- 

 restrial magnetism, than the conclusion which has been established 

 by means of the observations of the Declination at St. Helena, that 



