106 :Mf. Christie on the Magtielism of Iron [A 06. 



has long ago attracted the attention of conchologists, and it 

 also has been observed greatly to influence the form of the 

 Anomiiie, for when they are attached to pectens and other; 

 radiated shells, they are marked by their sculpture ; but I am 

 not aware that this fact has ever been observed to take place in 

 any of the other genera of bivalve shells, and especially in 

 those which are thick and ponderous. The specimen of Hin- 

 nita giganteuy which is in the museum, has evidently been 

 attached to a rock which had some large serpulae growing on it, 

 the edges of the valves, when growing, conformed them- 

 selves to the surface, and consequently the upper valve has the 

 convex lines across, which exactly correspond with the convo- 

 lutions on the outer surface of the lower one ; now at first sight 

 one might be led to believe, as indeed several of my friends have 

 been, that the convexity of the under valve, by pressing up the 

 body of the animal, has consequently raised the upper surface 

 of that part of the body, but in several places the upper valve is 

 marked externally where there are no traces of it in the inner 

 surface of either valve, nor are the upper valves of oysters 

 affected when the lower valves have very large pearls on them, 

 which must considerably displace the body of the animals. 

 Indeed, to any one who studies the formation of shells, I 

 think it must be evident that these raised places must be 

 formed as I have stated, by the edge of the upper valves con- 

 forming themselves when deposited to the bend of the lower 

 valves ; and when the causes which produced these curves are 

 removed, the valves resume the usual form, leaving the convex 

 line on the outside, the concavities of the inner part of the upper 

 valve being obliterated by the new layers of shell. 



Article V. 



Abstracts of Papers in the P/iilosophical Transactions for 1(S25, 

 on the peculiar Magnetic Effect induced in Iron, and on the 

 Magnetism manifested in other Metals^ &^c. during the Act of 

 Rotation. By Messrs. Barlow, Christie, Babbage, and 

 Herschel. 



2. On ike Magnetism of Iron arising from its Rotation, 

 By S. H. Christie, Esq. MA. FRS. 



{Continued from p. 43.) 



" Experiments with the Dipping Needle, 

 " Having found, in all the experiments which I have de- 

 scribed, that the effects produced on the horizontal needle 

 depended on the situation of the plate with respect to the axis 

 and equator of an imaginary dipping needle passing through 



