50 
PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
manifest that every pair parallel to the line d e represents a stronger mechanical 
couple than every corresponding pair parallel to fg. The consequence is, that a cube 
of crystallized bismuth suspended in the manner described, in a sufficiently uniform 
field of magnetic force, will move in the same direction as the cross in fig. 4 : its 
centre of gravity will therefore approach the pole N, which was to be demonstrated. 
This deduction is perfectly illustrated by experiment. It is manifest that the effect 
of the pole S upon the cube adjacent to it is to increase the moment of rotation of 
the rectangular box : the same reasoning applies to it as to the pole N, 
Referring to fig. 27 a, page 41, it will be seen that we have here dealt with the 
second and gravest objection of M. Matteucci, and converted the facts upon which 
the objection is based into a proof of diamagnetic polarity, so cogent that it alone 
would seern to be sufficient to decide this important question. Holding the opinion 
entertained by M. Matteucci regarding the nature of diamagnetic force*, his objec- 
tion must have appeared to him to be absolutely unanswerable: I should be glad to 
believe that the remarks contained in this ‘Appendix’ furnish, in the estimation of 
the distinguished philosopher referred to, a satisfactory explanation of the difficulty 
which he has disclosed. 
Let me, in conclusion, briefly direct the reader’s attention to the body of evidence 
laid before him in the foregoing pages. It has been proved that matter is repelled 
by the pole of a magnet in virtue of an induced condition into which the matter is 
thrown by such a pole. It is shown that the condition evoked by one pole is not 
that which is evoked by a pole of an opposite quality — that each pole excites a con- 
dition peculiar to itself. A perfect antithesis has been shown to exist between the 
deportment of paramagnetic and diamagnetic bodies when acted on by a magnet 
alone, by an electric current alone, or by a magnet and an electric current combined. 
The perplexing phenomena resulting from molecular structure have been laid open, 
and the antithesis between paramagnetic and diamagnetic action traced throughout. 
It is further shown, that whatever title to polarity the deportment of a bar of soft iron, 
surrounded by an electric current, and acted on by other magnets, gives to this sub- 
stance, a bar of bismuth possesses precisely the same title : the disposition of forces 
which, in the former case, produces attraction, produces in the latter case repulsion, 
while the repulsion of the iron finds its exact complement in the attraction of the 
bismuth. Finally, we have a case adduced by M. Matteucci which suggests a 
crucial experiment to which all our previous reasoning has been submitted, by which 
its accuracy has been proved, and the insufficiency of the assumption, that the dia- 
magnetic force is not polar, is reduced to demonstration. When we remember that 
against all this no single experimental fact or theoretic argument'f which can in any 
* II ne peut exister dans les corps diamagnctiques une polaritd telle qu’on la concoit dans le fer doux .” — Cours 
Special, p. 201. 
t I ought perhaps to excej)t an argument of Professor W. Thomson’s, which professes to prove that an 
absolute creation of force, and the setting up of a perpetual motion, would follow, if diamagnetic polarity were 
