12 Messrs. J. Tyndall and H. Knoblauch on the 



themselves in M. Plucker's experiments: — "On the develop- 

 ment of the magnetic force, the crystal went up to its position 

 slowly, and pointed as with a dead set. Other crystals did 

 the same imperfectly ; and others again made one or perhaps 

 two vibrations, but all appeared as if they were moving in a 

 thick fluid, and were, in that respect, utterly unlike bismuth, 

 in the freedom and mobility with which it vibrated. If the 

 crystalline mass was revolving when the magnetic force was 

 excited, it suddenly stopped, and was caught in a position 

 which might, as was found by experience, be any position. 

 The arrest was followed by a revulsive action on the discon- 

 tinuance of the electric current*." 



In most of the specimens examined by us these phenomena 

 were also absent, and the results of M. Pliicker presented 

 themselves. Three specimens however behaved exactly in 

 the manner described by Mr. Faraday, exhibiting a singular 

 inertness when the magnetic force was present, and a revul- 

 sion from the poles on breaking the circuit. To ascertain, if 

 possible, the cause of this difference, we dissolved an example 

 of each class in muriatic acid, precipitated the antimony with 

 distilled water, and tested the clear filtrate with ferrocyanide 

 of potassium. The specimen which agreed with M. Pliicker 

 exhibited a faint bluish tint, characteristic of the presence of 

 iron ; that which corroborated Mr. Faraday showed not the 

 slightest trace of this metal. The iron, though thus revealing 

 itself, must have been present in a quantity exceedingly mi- 

 nute, for the antimony was diamagnetic. Whether this has 

 been the cause of the difference between M. Pliicker and Mr. 

 Faraday we will not undertake to say; irregular crystalline 

 structure may also have had an influence. 



We have here a crowd of examples of crystalline action 

 in the magnetic field, but as yet not a word of explanation. 

 M. Plucker's hypothesis has evidently failed. We now turn 

 to the observations of Mr. Faraday, and shall endeavour to 

 exhibit, in the briefest manner possible, the views of this pro- 

 found investigator. 



After a general description of the action of bismuth between 

 the poles, Mr. Faraday writes : — ct The results are, altogether, 

 very different from those produced by diamagnetic action. 

 They are equally distinct from those dependent on ordinary 

 magnetic action. They are also distinct from those discovered 

 and described by Pliicker, in his beautiful researches into the 

 relation of the optic axis to magnetic action ; for there the 

 force is equatorial, whereas here it is axial. So they appear 



* Philosophical Transactions, 1849, p. 14. For an explanation see Phi- 

 losophical Magazine, vol. xxviii. p. 460. 



