1870.] ( 501 ) 



NOTICES OF SCIENTIFIC WORKS. 



Researches on Diamagnetism and Magne-crystallic Action, includ- 

 ing the Question of Diamagnetic Polarity. By John Tyndall, 

 LLJX, F.B.S., Professor of Natural Philosophy in the lioyal 

 Institution. London : Longmans, 1870. 



L O x 



This work is the first instalment of a complete collection of the 

 original memoirs on experimental physics, which the learned author 

 has published during the last eighteen years. It contains not 

 only a record of his own work on the subject of diamagnetism, but 

 also extracts from the writings of Faraday, Plucker, Becquerel, 

 Matteucci, Weber, and other experimental philosophers, bearing 

 upon the same phenomena, so that the reader has before him every- 

 thing necessary for a complete understanding of this very intricate 

 subject. The second part of the book contains letters, essays, and 

 reviews, relating to magnetism and electricity, and includes among 

 others a discussion on the existence of a magnetic medium in space, 

 the relation between magnetism and the electric current, an account 

 of the polymagnet, and one of the clearest descriptions of Ohm's 

 theory which we have ever read. 



We are so accustomed to see a magnetic substance like iron or 

 a magnetic needle point north and south, rush to the poles of a 

 magnet when brought near to one, or arrange itself axially when 

 suspended between the poles, that it is difficult to imagine that the 

 vast majority of substances possess almost diametrically opposite 

 qualities. When brought near to a magnet of sufficient power they 

 are repelled from it, and when suspended freely between its poles 

 they swing round, if of an elongated form, and arrange themselves 

 equatorially or at right angles to the line joining the two poles, 

 apparently with the object of getting as far away from them as 

 possible. This action was named by Faraday "Diamagnetism" 

 the common phenomena exhibited by iron being named " Paramag- 

 netism" whilst Magnetism is used as a general term to include the 

 whole range of both phenomena. Paramagnetic bodies are few in 

 number, but they include some of extraordinary energy, iron, nickel, 

 cobalt, and oxygen for instance ; whilst diamagnetic bodies include 

 the greater number of the metals, and such substances as rock 

 crystal, heavy spar, sulphate of magnesia, marble, alum, common 

 salt, saltpetre, carbonate of soda, Iceland spar, tartaric acid, citric 

 acid, water, alcohol, ether, the mineral acids, glass, iodine, phos- 

 phorus, sulphur, resin, spermaceti, sealing-wax, turpentine, india- 

 rubber, sugar, starch, gum arabic, wood, fresh beef, blood, apple, 

 bread, &c. In fact, could a marble statue, or its living prototype, 



