Magneto-optic properties of Crystals. 1 9 



polarity parallel to the lines of magnetic force. In this ex- 

 periment therefore the model of carbonate of iron, though a 

 magnetic body and strongly attracted by such a magnet as 

 that used, actually receded from the magnet. 



If, instead of the model of carbonate of iron, we substitute 

 a crystal of sulphate of iron, we have Mr. Faraday's experi- 

 ment instituted to prove the absence of attraction or repulsion. 

 The dimensions are his dimensions, the arrangement is his 

 arrangement, and the deportment is the exact deportment 

 which he has observed. We have copied his very words, 

 these words being perfectly descriptive of the action of the 

 model. If, then, the experiment be " a striking proof that 

 the effect is not due to attraction or repulsion " in the one 

 case, it must also be such in the other case; but the able ori- 

 ginator will, we imagine, hardly push his principles so far. 

 He will, we doubt not, be ready to admit, that it is more pro- 

 bable that a line of elective polarity exists in the crystal, than 

 that a magnecrystallic axis exists in the model *. 



By a similar proceeding, using bismuth powder instead of 

 carbonate of iron, the action of Mr. Faraday's plate of bis- 

 muth may be exactly imitated. The objection to the conclusion, 

 that the approach of the magnecrystallic axis, in bismuth, to the 

 magnetic resultant, is due to the repulsion of the planes of clea- 

 vage, is thus, we conceive, fairly met. 



Let us look a little further into the nature of this magne- 

 crystalllic force, which, as is stated, is neither attraction nor 

 repulsion, but gives position only. The magnecrystallic axis, 

 says Mr. Faraday, tends to place itself parallel to the magnetic 

 resultant passing through the crystal; and in the case of a 

 bismuth plate, the recession from the pole and the taking up 

 of the equatorial position is not due to repulsion, but to the 

 endeavour the bismuth makes to establish the parallelism 

 before-mentioned. Leaving attraction and repulsion out of 

 the question, we find it extremely difficult to affix a consistent 

 meaning to the words { tends ' and ' endeavour.' " The force 

 is due," says Mr. Faraday, " to that power of the particles 

 which makes them cohere in regular order, and gives the mass 

 its crystalline aggregation, which we call at times the attraction 

 of aggregation, and so often speak of as acting at insensible 

 distances." We are not sure that we fully grasp the meaning 

 of the philosopher in the present instance; for the difficulty 

 of supposing that what is here called the attraction of aggre- 

 gation, considered apart from magnetic attraction or repulsion, 



* The term magnecrystallic axis may with propriety be retained, even 

 should our views prove correct ; but then it must be regarded as a subde- 

 nomination of the line of elective polarity. 



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