252 Professor Forbes^s Address to the British Association. 



cial speculation, might have been expected in a country like 

 ours to have been more specifically treated of than it has been. 

 It strictly belongs to the dynamics of the science, to which, 

 since the time of Hutton, but little attention has been paid un- 

 til very recently. By the exertions, however, of Mr Carne, of 

 Dr Boase, and Mr Hen wood of Cornwall, whose researches are 

 to form one point of discussion in the Geological Section at the 

 present meeting, the question of the origin of Mineral Veins, 

 though probably by no means decided, has been brought pro- 

 minently forward. 



That Electric Agency was concerned in the disposition of me- 

 talliferous veins can scarcely be doubted ; and the connection 

 between electricity and magnetism, now so fully established, — 

 the connection between metalliferous veins and lines of ele- 

 vation, and between the latter and the isodynamical lines of 

 terrestrial magnetic intensity, as suggested by Professor Necker 

 of Geneva, — point out a bond of union between this subject and 

 that of terrestrial magnetism, on which we have a report by 

 Mr Christie, where the very interesting direct observations of 

 Mr Fox of Falmouth, on the electro-magnetic action of mineral 

 veins, are particularly noticed. Mr Christie's theory of the 

 diurnal variation of the needle, which he is desirous should be 

 submitted to the test of a laboratory experiment, is likewise in- 

 timately connected with the actual constitution of our globe *. 

 The whole subject of Terrestrial Magnetism, is one of the 

 most interesting and progressive of the experimental sciences. 

 The determination of the direction of the magnetic energy by 

 means of two spherical co-ordinates, termed the variation and 

 the dip, and the measure of the intensity/ of that force, are the 

 great objects of immediate research, as forming a basis of theory. 

 The existence of four points on the earth's surface, to which 

 the needle tends, has long been known ; and the position of two 

 of these (in Northern Asia and America,) has recently been 

 elucidated by the persevering efforts of Professor Hansteen and 

 Commander Ross. The precise numerical determination of the 

 elements just alluded to, acquires a deep and peculiar interest 

 from the multiplied variations which they undergo. Not only 



" ' * Report, p. 122-3. 



