TERRESTRIAL MAGNETISM. 3.5 



discovery, have been such as to afford results incapable of beinaj 

 depended on to any minute degree of precision, calculated only 

 to satisfy the immediate practical wants of the ordinary na- 

 vigator ; and, so far as theory is concerned, to give a general 

 view of the course of the magnetic lines in those parts of the 

 globe which have chiefly been the scenes of inquiry, and to es- 

 tablish the important facts of changes more or less rapid taking 

 place in the intensity and direction of the magnetic forces at 

 every point of its surface. 



Of late, however, methods infinitely more perfect have been 

 devised and practised in Germany (whence their use has ex- 

 tended to other nations in Europe), which have given to mag- 

 netic determinations a precision previously supposed to be un- 

 attainable — a precision not inferior to that of astronomical ob- 

 servation. The time is therefore now arrived when all that is 

 rude and inexact in the subject of terrestrial magnetism must 

 give place to rigorous numerical statement and refined discus- 

 sion ; and, when a theory can exist, which, like those of the 

 planetary movements, basing itself on a few perfectly ascer- 

 tained elements, shall embrace in general formulae all the in- 

 tricacies of the subject — define a priori the course of the mag- 

 netic lines over the whole surface of the globe, and retrace or 

 predict their variations for centuries past or to come. 



To ascertain these elements with all the strictness which 

 human skill and industry can command ; to investigate, by 

 systematic, and, when necessary, by co-operative observation, 

 those inductive laws which must serve as the stepping stones of 

 such a theory, and to amass a series of well concerted and ef- 

 fective observations, of sufficient accuracy and extent to serve as 

 tests of its truth — have appeared to the British Association for 

 the Advancement of Science objects of such eminent importance 

 as to justify it in recommending them to Her Majesty's Go- 

 vernment, as worthy of some considerable national exertion 

 and expenditure. Private research has done much, and is 

 doing more, and the practical bearings of the subject may 

 possibly stimulate commercial bodies to afford some slight 

 and incidental aid in the inquiry ; but there are features in the 

 case which lead us to conclude that without the co-operation 

 of Government on an extensive scale, the resources of science 

 must be employed in vain, or a^ a disadvantage which must 

 retard indefinitely the desired consummation. 



For, in the first place, the observations necessary for the 

 purpose in view require to be made at many very distant points 

 of the globe, for a considerable length of time, and (what is 

 particularly to be noticed) at moments strictly simultaneous. 



1839. D 



