504 Notices of Scientific Works. [Oct., 



and suspending it freely in the neighbourhood of the crystal. The 

 tendency of the needle was always to place itself parallel to the 

 magne-crystallic axis. 



Neither will space permit us to refer, except in the briefest 

 manner, to the results obtained by preparing bars of magnetic and 

 diamagnetic substances, by reducing them to fine powder, and then 

 compressing them in moulds in such a manner that the line of 

 greatest compression is in different directions along or across the 

 bar. A bismuth bar so prepared, squeezed flat within the jaws of 

 a vice and suspended between the poles, will turn with the energy 

 of a magnetic substance into the axial position ; whilst a bar made 

 up of powdered carbonate of iron (magnetic) compressed in this 

 manner will recoil from the poles as if violently repelled. It thus 

 appears that the line of magnetic action has a near relation to that 

 of the closest contact among the material particles, and this rela- 

 tionship is traced in many different ways, and appears related to 

 the cleavage of crystals. 



It would be of interest to try some of these experiments on 

 diamagnetism with the metal Thallium, a metal which, whilst it 

 rivals, if it does not surpass, bismuth in diamagnetic energy, is as 

 soft and amorphous as lead, and lends itself with the same facility 

 to moulding and compression. Probably many of the apparent 

 anomalies of diamagnetism which observers at first encounter, owing 

 to the highly crystalline nature of bismuth, would disappear if 

 thallium were the metal selected for experiment. 



"We cannot close this book without expressing the profound 

 admiration which it leaves in the mind for the author's philosophical 

 acumen and experimental skill. He moreover possesses one valu- 

 able quality, which we regret to say is as rare amongst scientific 

 men as the combination of the two former, — that of placing his views 

 and describing his experiments in such clear language that the 

 profoundest mysteries of nature seem under his treatment to become 

 clear and simple to a child's comprehension. Speaking as one who 

 never loses an opportunity of listening to this philosopher on 

 whom the mantle of Faraday has so worthily descended, the writer 

 scarcely knows which gives him greater pleasure — to listen to one of 

 Dr. Tyndall's lucid expositions of some hitherto hidden mystery of 

 nature, or to hear him in his clear logical manner quietly put down 

 a scientific opponent who has ventured to differ from some of his 

 conclusions. 



