Dr. Fitton's Notes on the History of English Geology. 37 



direction, in front oi the metallic poles; whilst but very trifling 

 deflections of the polar lines are to be seen, along the edges of 

 the magnet: even on the outside of the limbs the aberrations 

 are much less than those exhibited on the surface of the bar 

 magnet fig. 3. at similar distances from the poles. 



In this case the magnetic polar lines maintain their natural 

 rectilinear direction, even at considerable distances from the 

 extremities of the metal, and particularly between the limbs 

 of the magnet; in consequence of the two systems emanating 

 from the metallic surface in diametrically opposite directions, 

 and meeting each other, as it were, in the same rectilinear path. 

 On the outside of the limbs, the aggregate of the two systems 

 of polar lines, in the plane of the magnet, are not only so far 

 separated from each other as to be little affected by their mu- 

 tual attraction, but are also so situated with regard to the 

 transverse curvilinear forces (see fig. 5.), that they form a 

 series of resultant right lines in the plane of the magnet. 

 These lines have, however, a small degree of flexure from their 

 natural course, arising from their mutual attractions in the 

 direction of the metal, which bend them a little towards the 

 centre of the magnet. 



Having thus illustrated what I consider to be the virtual 

 polar magnetic lines, and also their most usual arrangements 

 in the vicinity of steel, or other ferruginous magnets, I now 

 propose to show that the excitation of magnetic electricity, 

 and also the direction of the currents excited, are referable to 

 the agency and position of these polar magnetic lines alone ; 

 without any regard whatever to the poles, figure, or position 

 of the steel which they envelop ; any further than as those lines 

 are casually arranged on its surface, by the diverse arbitrary 

 forms and proportions it is so frequently made to assume. 



[To be continued.] 



XI. Notes on the History of English Geology. By 

 William Henry Fitton, M.D. ER.S. %c*. 



[Concluded from vol. i. p. 450.] 

 [With a Plate.] 



HPHE geological publications of Mr. Smith are now so well 



-*■ known, and the progress of the author's researches has 



been sketched with so much truth and spirit by Mr. Sedgwick, 



in one of his addresses from the chair of the Geological So- 



* [The whole of the subsequent pages, as well as some passages in the 

 preceding parts of this paper, which are between brackets, are recent 

 additions to the original as reprinted in 1821.] 



