Dr. C. Fromme on the Magnetism of Steel Bars. 293 



of tremolite, and imbedded in saponite : tlie smallest tube-like forms 

 appear as if they were empty. Magnified 37 diameters. 



Fig. 18. Longitudinal section of the same (at the part lying immediately 

 in contact with calcite). Magnified 37 diameters. 



Fig. 19. A body composed of tremolite simulating a Globigerina. Mag- 

 nified 37 diameters. 



Fig. 20. Spherical bodies composed of flocculent (white) and amorphous 

 (pale green) serpentine, with a perforated exterior resembling the shell 

 of Orbulina. Two have a core of saponite (fawn-colour). These bodies 

 are contained in a mass of tremolite imbedded in saponite. Mag- 

 nified 37 diameters. 



Fig. 21. A mass of tremolite imbedded in serpentine, and consisting of a 

 sponge-like tissue with its walls perforated. The large dark portions 

 represent what appear to be the mouths of canals. Magnified 37 

 diameters. 



Fig. 22. A crystallized specimen of tremolite composed of fasciculi : its 

 free end was imbedded in calcite, now removed by decalcification. 

 The upper fasciculi are either fibrous or prismatic. Many of the 

 prisms have white opaque bounding planes and a translucent interior. 

 The lower fasciculi are altogether translucent, with the exception of 

 their boundary surfaces, which latter form a network with large meshes. 

 Slightly magnified. 



XXXIV. On the Magnetism of Steel Bars. By Dr. Carl 

 Fromme, Instructor in Physics at the University of Gottingen. 



[Concluded from p. 204.] 



§ 9. (\N the occasion of these experiments I noticed some 

 vj/ relations which were quite new to me ; and they 

 appeared so extremely interesting that I resolved to pursue 

 them further. It was only after I had finished a great part of 

 these investigations (which shall now be communicated in what 

 follows), that I observed, on perusing the literature, that the 

 same subject had already, some years since, attracted the atten- 

 tion of Frankenheim. His results were published in Poggen- 

 dorff's Annalen, vol. cxxiii. p. 49 et seq. 



Frankenheim proves that the duration of the action of a 

 magnetizing force has no influence at all upon the amount of 

 the residual magnetism, while the number of operations of the 

 same force has a very great influence. If it has been put in ope- 

 ration only once, we have not thereby attained the residual 

 moment which the same force generally (i. e. by repeated 

 action) is capable of generating. The residual magnetism is 

 increased much more by each successive operation, approxi- 

 mating to a boundary value, above which the same force can- 

 not raise it. 



From this I deduce the significant conclusion, confirmed by 

 experiment, that when by repeated action of the force P the 

 residual magnetism has reached its boundary value (the satu- 



