401 



night ; the corresponding variations attain their maximum, at Ho- 

 oarton, also during the hours of the night, hut with a small systematic 

 difference as to the precise hour, and with this distinguishing pecu- 

 liarity, 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 at a third station, St. Helena, which is a tropical 

 one, the hours of principal disturbance are those not of the night, 

 but of the day. A very superficial examination is sufficient to show 

 that for the generalization of the facts, a generalization which is 

 indispensable for their correct apprehension and employment in the 

 formation of a theory, the stations at which the phenomena are to 

 be known must be increased. Those which were chosen for a first 

 experiment were well selected to prove the importance of the inves- 

 tigation, and thus to lead to its extension. It is only at the Colonial 

 Observatories that the disturbance-variations have hitherto been made 

 out ; and taking experience as our guide, we have before us the evi- 

 dence of the means by which the inquiry may be further successfully 

 prosecuted*. 



Periodical Variations. The anticipation expressed in the Report 

 of the Committee of Physics, that for the purpose of obtaining a cor- 



* The Colonial Observatories under my superintendence were originally four in 

 number, viz. Toronto, St. Helena, Cape of Good Hope, and Hobarton. In July 

 1846 the detachment of the Artillery at the Cape of Good Hope was withdrawn 

 by orders from England, and the charge of the magnetical and meteorological ob- 

 servations transferred to Mr. Maclear, the Government Astronomer at that station. 

 The magnetical observations made at the Cape, when the magnetic observatory 

 was one of those under my superintendence, were published in 1851, with a dis- 

 cussion of certain of their results ; and the disturbance-variation of the declina- 

 tion at the Cape has since been deduced by my assistant, Captain Younghusband, 

 Phil. Trans. 1853, Art. VI. Since the transfer to Mr. Maclear, Mr. Pierce 

 Morton, a gentleman of considerable mathematical attainments, who has been 

 added as an assistant to Mr. Maclear in that branch of the Cape observations, 

 has applied himself to the investigation of the lunar magnetic influence (as derived 

 from the Cape observations), with a view of presenting the results to the Royal 

 Society. For this, and other deductions, such as, for example, the laws of the 

 disturbances of the inclination and total force, he will have the entire series of 

 observations, viz. those as above-stated already published, and those which have 

 been made since the transfer of the Observatory, up to the present time. 



