1864.] 



Disturbances at Kew and Nertschinsk, 



249 



together with all that is not permanent in the phenomena, whether it 

 appear in the form of momentary, daily, monthly, semiannual, or annual 

 change, or in progressive changes receiving compensation possibly, either 

 in whole or in part, in cycles of unknown relation and unknown period." 

 The magnetic disturbances to which the notices in the present paper are 

 limited, form a small but important branch of this extensive inquiry, and are 

 referred to in the instructions prepared by the Royal Society in terms which 

 are recalled by the author on the present occasion, because they are ex- 

 planatory of the principles on which the coordination of the results ob- 

 tained in such distant parts of the world has been conducted, and the 

 conclusions derived from them established. In pages 2 and 3 of the 

 Report embodying the instructions drawn up by the Royal Society, it is 

 stated that the investigation of the laws, extent, and mutual relations of 

 the casual and transitory variations is become essential to the success- 

 ful prosecution of magnetic discovery .... because the theory of those 

 transitory changes is in itself one of the most interesting and important 

 points to which the attention of magnetic observers can be turned, as they 

 are no doubt intimately connected with the general causes of terrestrial 

 magnetism, and will probably lead us to a much more perfect knowledge 

 of those causes than we now possess." In the opinion thus expressed, the 

 author, who was himself one of the committee by whom the Report was 

 drawn up, fully concurred ; and having been appointed by Her Majesty's 

 Government to superintend the observations made at the British Colonial 

 observatories, and to coordinate and publish their results, he has endea- 

 voured to show in this paper that the methods pursued have been in strict 

 conformity with these instructions, and also that the conclusions derived are 

 in accordance with the anticipations expressed therein. 



Inferences regarding the " general causes of terrestrial magnetism " 

 must be based upon the knowledge we possess of the actual distribution of 

 the magnetic influence on the surface of the globe, since that is the only 

 part which is accessible to us. In regard to this distribution, the Report 

 itself refers continually to two works, then recently published, as contain- 

 ing the embodiment of the totality of the known phenomena, viz. a 

 " Memoir on the Variations of the Magnetic Force in different parts of the 

 Earth's Surface," published in 1838 in the Reports of the British Associa- 

 tion, and M. Gauss's ' Allgemeine Theorie des Erdmagnetismus,' published 

 in 1839. In both these works the facts, as far as they had been ascertained, 

 were conformable in their main features to the theory, first announced by 

 Dr. Halley in his Papers in the Philosophical Transactions for 1683 and 

 1693, of a double system of magnetic action, the direction and intensity 

 of the magnetic force being, at all points of the earth's surface, the 

 resultants of the two systems. In both these works the Poles, or Points 

 of greatest force (in the northern hemisphere) were traced nearly to the 

 same localities — viz. one in the northern parts of the American continent, 

 and the other in the northern parts of the Europaeo-Asiatic continent,- — their 



