1853.) OF THE ROYAL INSTITUTION. 257 
and in magnetic bodies axial. A reference to this principle will 
instantly render plain all the experiments we have described. In 
those cases where the same artificial bar set at one time axial and 
at another time equatorial, the deportment depended on the circum- 
stance whether the line of compression was vertical or horizontal. 
When vertical its directive power was annulled, and the action 
was determined by the exterior form of the body; but when 
horizontal its directive action came into play and determined the 
position of the mass. The magnetic bar, for example, suspended 
with its line of pressure vertical, set axial, but with its line of 
pressure horizontal, it set equatorial; for the pressure was exerted 
at right angles to its length. This action is so general that it is 
difficult to finda body so perfectly homogeneous as not to exhibit it 
in some degree. Ipecacuanha lozenges and Carlisle biscuits were 
suspended in the magnetic field and exhibited a most striking 
directive action. The materials in both cases were diamagnetic ; 
but owing to the pressure exerted in their formation their largest 
horizontal dimensions set from pole to pole, the line of compression 
being equatorial. 
Let us endeavour to arrive at the precise logical import of these 
experiments. Let us suppose that before ever a crystal had been 
suspended in the magnetic field, we were acquainted with the fact 
that a slight change of density in any direction is accompanied by 
such modifications of the magnetic force as those above described : 
— that we knew that flour, bran, soap, shale, magnetic dust, diamag- 
netic dust, &c., al] exhibited this directive action, — that it is in fact 
a universal law of matter; and then let us imagine some fortunate 
experimenter hanging a crystal between the poles and observing a 
deportment in every respect similar. Would not the analogy of 
the case at once flash upon him? Would he not regard this de- 
portment as a beautiful, but still special example of that all-pervading 
law with which he was previously acquainted. Would he not con- 
gratulate himself on the possibility thus opened to him of searching 
out the mysteries of crystalline structure, and rendering apparent to 
his mental eye the manner in which the molecules are aggregated 
together. He would never have assumed the existence of forces al- 
together new to account for the observed actions ; much less would 
he have affirmed that they were wholly independent of magnetism or 
diamagnetism ; for he would know beforehand that the modification 
of these forces by the peculiarities of aggregation was the exact 
thing calculated to produce the phenomena. But magne-crystallic 
action was discovered when its universality was unknown; and 
hence its discoverer was led to regard it as something unique. A 
great temptation lay in his way: years before, a magnet, now 
present, had twisted a ray of light, and thus suggested a connexion 
between light and magnetism. What wonder then if this unifying 
instinct, this yearning to find the mystic bond which unites these 
forces, this prediction of the human mind that all the forces of 
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