Magnetized Non-crystalline Substances. 251 



posed to the following conclusion to which M. Pliicker arrives, 

 from some of his experimental researches : — "J'ai deduit de 

 la cette loi generate, savoir : que le diamagnetisme decroit 

 plus vite que le magnetisme quand la force de 1'aimant dimi- 

 nue, ou quand la distance des poles augmente " * : but many 

 of the curious phenomena from which M. Pliicker was led 

 to this conclusion, and which he adduces in confirmation of 

 it, do not appear to me to support it, but rather to be con- 

 nected with the peculiar magneto-inductive properties of cry- 

 stalline or quasi-crystalline structure which he discovered 

 subsequently t ; and with respect to those which appear at 

 first sight really to support it, I have conjectured that they 

 may admit of explanation solely on the principle expressed in 

 Faraday's law, quoted at the commencement of these remarks. 

 Thus, the experiments upon a watch-glass containing mer- 

 cury, placed at different distances from a magnet, which show 

 that the resultant force experienced by the watch-glass, in 

 virtue of its own magnetization as a ferromagnetic substance, 

 and the contrary magnetization of the diamagnetic mercury, 

 is sometimes increased by removing the whole to a slightly 

 greater distance from the magnet, do not prove that when the 

 magnetizing force is diminished the induced magnetization of 

 the mercury is diminished by a greater fraction of its former 

 amount than that of the watch-glass, but are most probably 

 to be explained by the circumstance that the " field of force" 

 occupied by the mercury and watch-glass, when removed a 

 very short distance, is such that the mean value of the differ- 

 ential coefficient of the square of the force, with reference to 

 co-ordinates parallel to the direction of motion of the watch- 

 glass, is greater than the mean value of the same function, 

 through the field occupied when the watch-glass is in contact 

 with the magnet. It is of course impossible to give more than 

 a general explanation such as this without some specific know- 

 ledge of the distribution of magnetic force in the neighbour- 

 hood of the actual magnet employed ; but the phenomena 

 described by M. Pliicker in this case are undoubtedly of a 

 kind that might be anticipated if a vertical bar-magnet be 



* Quoted from a paper in the French Annales de Chimie et de Physique, 

 June 1850, bearing the title, " Sur le Magnetisme et le Diamagnetisme : 

 par M. Pliicker." This paper appears to be a resume of the author's ex- 

 perimental researches and discoveries regarding magnetic induction, of 

 which detailed accounts have been published in various communications to 

 PoggendorfF's Annalen in the course of the last two years. 



\ This connection is recognized by the discoverer himself, as is shown by 

 the statement he makes at the commencement of § 4 of the paper already 

 referred to. Yet he mentions his experiments on cylinders of charcoal as 

 the foundation on which he establishes, as a general law, the conclusion 

 quoted in the text. 



