Royal Institution. 307 



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 aesumed 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 phsenomena. But magnecrystallic 

 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 

 nature are but branches of a common root, — what wonder, 1 say, if 

 it jumped its bounds and cried " I have it ! " too soon ? For a 

 long time the optic axis, and it alone, was chargeable with these 

 phsenomena, — phsenomena which it was now hoped there would be 

 little difficulty in referring to their proper cause, and regarding as 

 examples of the modification of force by the peculiarities of aggre- 

 gation. 



The Lecturer then pointed out the bearing of the described results 

 upon the problem of the diurnal range of the magnetic needle. Pro- 

 fessor Faraday had referred the matter to the modification of atmo- 

 spheric magnetism by the sun's rays*. That an effect was produced 

 here could not for a moment be doubted, but the precise extent of 

 this eff^ect was still an open question. The discovery of a decimal 

 period by Lamont threw a great difficulty in the way of any theory 

 which would refer the diurnal range to thermic action ; and the 

 diflEiculty was greatly increased by the observation of Col. Sabine, 

 who connected Lamont's discovery with that of Schwabe regarding 

 the solar spots. But whatever the result of future inquiries as to 

 the direct magnetism of the sun may be, no theory which proposes 

 to exhaust the subject can aflford to omit the mediate operation of 

 the sun by his heat ; not however confining it to the atmosphere, but 

 extending it also to the earth's solid crust. Let us look once more 

 to our experiments. The line of greatest density is that of strongest 

 magnetic power. The body operated upon by the magnet is itself a 

 magnet, and it is an experimental fact, that it is a stronger magnet 

 along the line of greater density than along any other line. If 

 instead of increasing the density in one direction we increase it in all 

 directions, we thereby augment the general magnetic power of the 



* Phil. Mag. March 1863. 



