for the Advancement of Science. 271 



unvarying result: — the line of compression stood always equatorial, 

 and it was a matter of perfect indifference whether this line was the 

 magnecrystallic axis or not. In these cases no gum was used, and not 

 only was a predominance of axes present, but they all worked togeth- 

 er; they we.TQ further assisted by the great mechanical advantage offer- 

 ed by such plates to diamagnelic repulsion ; the line of compression 



nevertheless triumphed over all and determined the position of the 

 crystal. 



The author concludes his paper as follows : "Whoever denies the 

 influence of proximity will have to answer the following questions: 

 How is it possible that a greater differentia! action can be exhibited by 

 a cube of bismuth dough, than by the crystal itself? What is it which 

 causes the magnecrystallic axis to forsake its usual position, and to set 

 equatorial when the crystal is compressed in the direction of that axis? 

 He must further assume a crystalline structure on the part of wax, 

 flour, shale, and the pith of fresh rolls; for in all these substances the 

 hne of compression determines the position of the mass in the mag- 

 netic field." • 



At the conclusion of the paper, Prof. Faraday rose, and spoke at 

 I some length on the valuable contribution to science which had been 



J -^ brought before them by Dr. Tyndall. It afforded him great gratifica- 



tion that there was one at least among us who had followed up this 

 important subject so perseveringly. The beautiful laws established by 

 -Dr. Tyndall proved the identity of magnetism and diamagnetism in 

 one important particular, — a result which he always anticipated; and 

 if the crystalline action could be explained by what might be called 

 the gross mechanical experiments brought before them, the discovery 

 wag one of the utmost consequence. It gave him pleasure to be 

 able to propose a question to one who had worked so long at the 

 foundations of this matter. Many philosophers had affirmed that it 

 was possible to convert attraction into repulsion, and vice versd^ by 

 Merely varying the magnetic power: this was contrary to his own ex- 

 perience, and he wished to ask Dr. Tyndall whether he had ever met 

 a case of the kind.^ — Dr. Tyndall stated in reply that he had diligently 

 I sought for such a case, but had never succeeded in finding it. 



Prof. Faraday felt prepared to admit that some of Dr. Tyndall's re- 

 stilts seemed to promise an explanation of Pliicker's perplexing results 

 and conclusions ; but for his own part he was anxious to keep his mind 

 free from bias, to get well-established facts, and to free them as much 

 . as possible from all circumstances which could mark, or disguise, or 

 "^;slead in the Interpretation of them,— and such being his fixed deter- 

 oiination and settled habit, he was rather at a loss to remember to what 

 portion of his publications on the subject Dr. Tyndall referred when 

 ?e supposed him to have considered the facts now brought forward as 



improbable. 



3, Report of the Kew MagnelograpTis ; by CoL Sabine. 



. The author said that at the request of the Council he was about to 

 give the Section a brief account o^ the experimental trial now making 

 at the Kew Observatory of Mr. Ronald's instruments for the self-regis- 

 ^•■y of the variations of terrestrial magnetism by means of photography. 



