BIOGRAPHICAL SKETCH 



when he took his degree. His first 

 physical paper, published in the Philo- 

 sophical Magazine for February, 1851, 

 was on "The Phenomena of a Water Jet" 

 a subject comparatively simple, but not 

 without scientific interest. 



In conjunction with Knoblauch, Tyn- 

 dall executed and published an impor- 

 tant investigation " On the Magneto- 

 optic Properties of Crystals and the 

 Relation of Magnetism and Diamag- 

 netism to Molecular Arrangement." 1 

 They claimed to have discovered the 

 existence of a relation between the 

 density of matter and the manifestation 

 of the magnetic force. Their funda- 

 mental idea was that the component 

 molecules of crystals, and other sub- 

 stances, are not in every direction at the 

 same distance from each other. The 

 superior magnetic energy of a crystal in 

 a given direction, when suspended 

 between the poles, they attributed 

 to the greater closeness of its mole- 

 cules in that direction. In support 

 of their assumption they showed that, by 

 pressure, the magnetic axis of a bismuth 

 crystal could be shifted 90 in azimuth, 

 the line of pressure always setting itself 

 parallel with, or at right angles to, the 

 line joining the two magnetic poles, ac- 

 cording as the crystal was magnetic or 

 diamagnetic. This explanation differed 

 essentially from that of Faraday and 

 Pliicker. In June, 1850, Tyndall went 

 to England, and at the meeting of the 

 British Association of that year in Edin- 

 burgh he read an account of his investiga- 

 tion, which excited considerable interest. 

 He afterwards returned to Marburg for 

 six months, and carried out a lengthy 

 inquiry into electro-magnetic attractions 

 at short distances. 2 



1 Phil. Mag. , July, 1 850. * Ib. , April, 1 85 1 . 



At Easter, 1851, Tyndall finally left 

 Marburg and went to Berlin, where he 

 became acquainted with many eminent 

 men of science. In the laboratory of 

 Professor Magnus he conducted a second 

 investigation on " Diamagnetism and 

 Magne-crystallic Action," 1 which formed 

 a sequel to that previously undertaken 

 with Knoblauch. A paper describing his 

 results was read at the Ipswich meeting 

 of the British Association. He showed 

 that the antithesis of the two forces 

 was absolute : diamagnetism resembling 

 magnetism as to polarity and all other 

 characteristics, differing from it only by 

 the substitution of repulsion for attrac- 

 tion and vice versa. 



The question of diamagnetic polarity 

 was much discussed. Its existence, 

 originally asserted by Faraday, and 

 reaffirmed by Weber in 1848, had been 

 subsequently denied by Faraday, who 

 still continued doubtful. To meet all 

 objections, Tyndall, at a later date, again 

 took up the subject, and in three con- 

 clusive investigations, the second of 

 which formed the subject of the Bakerian 

 lecture delivered before the Royal Society 

 in 1855, he put the polarity of bismuth 

 and other diamagnetic bodies beyond 

 question. 2 Five years were devoted by 

 him to the investigation of diamagnetism 

 and the influence of crystalline struc- 

 ture* and mechanical pressure upon the 

 manifestations of magnetic force. The 

 original papers (with a few omissions in 

 the last edition) are collected in his book 

 on Diamagnetism (see p. 12). 



Before leaving Marburg in 1851, 

 Tyndall had agreed to return to Queen- 

 wood ; this time as lecturer on mathe- 

 matics and natural philosophy. Here 



1 Phil. Mag., September, 1851. 



2 Ib., November, 1851 ; Phil. Trans., 1855; 

 ib., 1856, pt. i. 



