358 PLUCKEB ON THE THEORY OF DIAMAGNETISM. 



mena do not exhibit themselves if the crystal be first placed 

 in acid which dissolves the iron. I must now express my ad- 

 herence to the result of Faraday, that the axis of rock crystal is 

 neither attracted sensibly nor repelled by the poles of an electro- 

 magnet. 



Note. 



M. PlUcker complains of the false position in which the non- 

 publication of the foregoing memoir has placed him. It gives 

 me pleasure to do him the justice of placing it before the 

 English public. Granting, however, that the memoir had been 

 published with all possible despatch, it would, I imagine, but 

 slightly modify the tone and purport of the papers which have 

 since appeared upon the same subject. We have, for example, 

 the law regarding the attraction of the axes of positive crystals 

 and the repulsion of the axes of negative crystals restated in the 

 foregoing memoir. This, I believe, M. Pliicker himself now 

 admits to be an error. The turning of a crystal from the axial 

 to the equatorial position is also dwelt upon, a fact which formed 

 the basis of a most important general law ; but there is not the 

 slightest indication of the veritable cause of this phaenomenon, 

 that it is due to the action of the pointed poles made use of in 

 the experiments; nor can I gather even from the latest writings of 

 M. Pliicker, that he is as yet aware of the extent to which this 

 circumstance has vitiated his otherwise beautiful investigations. 

 In a note at the bottom of page 341, it is stated that it is not 

 meant to be asserted that the optic axis force is independent of 

 the magnetism or diamagnetism of the mass. Similar state- 

 ments are made in other publications of M. Pliicker. As long, 

 however, as his results remained uncontroverted, the inde- 

 pendence spoken of is constantly affirmed. The optic axis force 

 is called " a new force not hitherto indicated by any phaeno- 

 menon,^^ and an individuality is ascribed to it of the same order 

 as magnetism itself. No astronomer, I imagine, would think of 

 dividing the forces of the solar system into — 



1st. The force of gravitation ; 



2nd. The force which produces the precession of the equinoxes. 

 And yet, when we grant that M. Pliicker knew the relation 



