1865.] President's Address. 499 



establishment of a standard compass, in a fixed and suitable position, by 

 which compass alone the ship's course should be directed and all bearings 

 should be taken, and the formation of a table of deviations on the several 

 points of the compass by the method now so universally practised of 

 swinging the ship were adopted in both the 'Isabella' and the 'Alex- 

 ander.' The systematic character of the deviations, unprecedented in 

 amount, which were experienced by these ships in subsequent parts of their 

 voyage, attracted the attention of an eminent French geometrician, Poisson, 

 who published, in 1824, two papers in the Memoirs of the French Institute, 

 containing a mathematical theory of magnetical induction, with formulae in- 

 volving coefficients to be determined by observation, expressing the action 

 of the soft iron of a ship upon her compass and, in a subsequent memoir, 

 adapted the formulae to observations made on shipboard sufficient in num- 

 ber to determine the coefficients in the particular case of the soft iron 

 being symmetrically distributed on either side of the principal section of 

 the ship. The application of these formulae was verified by deviations 

 calculated for different positions in the high northern latitudes, where the 

 absolute values of the magnetic elements, as well as the deviations of the 

 compass on board, had been observed by the polar ships, the observed 

 and calculated deviations showing a remarkable accordance. 



About twenty years after the date of the Arctic voyages, the system of 

 compass-correction, which had been so successfully practised in the ships 

 engaged in those voyages, was definitely adopted in the Royal Navy, on the 

 recommendation of a committee appointed by the Admiralty, including 

 among its members two of the officers who had served on these voyages, 

 viz. the late Sir James Clark Ross and myself. 



At a somewhat later epoch the Magnetic Survey of the Antarctic regions 

 brought into prominent view the importance and value of Poissori's theory. 

 By far the greater part of the Survey having to be executed by daily ob- 

 servation of the three magnetic elements on shipboard, it became desirable 

 for the deduction of the results, that the fundamental equations of Pois- 

 son's theory should receive such a modification as should adapt them to 

 the form in which the data generally present themselves. This was the 

 first great service which Mr. Smith rendered towards the correction of the 

 irregularities occasioned by the magnetism of ships. Himself a mathe- 

 matician of the first order, and possessing a remarkable facility (which is 

 far from common) of so adapting truths of an abstruse character as to 

 render them available to less highly trained intellects, he derived, at my 

 request, from Poisson's fundamental equations, simple and practical for- 

 mula} including the effects both of induced magnetism and of the more 

 persistent magnetism produced in iron which has been hardened by any of 

 the processes through which it has passed. These formulae supplied the 

 means of a sufficiently exact calculation when the results of the Survey 

 were finally brought together and coordinated. They were subsequently 

 printed in the form of memoranda in the account of the Survey in the 



