Michael Faraday, his Life and Works. 433 



in a perfectly satisfactory manner, with the laws which govern 

 magnetism and diamagnetism. Subsequently Tyndall succeeded 

 also in demonstrating, by a decisive experiment, that diamag- 

 netism, like magnetism, is due to a polarity caused by the influ- 

 ence of the magnet in the diamagnetic body, but with this dif- 

 ference, that, instead of opposite poles, homonymous poles are 

 developed by the poles of the magnet. Thus fell to the ground 

 all the other more or less rash attempts at explanation which 

 had been given of diamagnetism. 



Another point which deserves attention is the investigation 

 which Faraday made of the magnetism and diamagnetism of 

 gases. He arrived at this curious result (observed likewise 

 by Edmond Becquerel at the same time), that of all gases oxy- 

 gen alone is magnetic, and this in a very marked degree, while 

 all the other gases are diamagnetic. Considering the great 

 part taken by oxygen in the composition of our atmosphere, 

 he attempted to explain, by the magnetic properties of this 

 gas combined with variations of temperature, the phenome- 

 non of the diurnal variations of the magnetic needle which 

 he traced over all parts of the surface of the globe. It is im- 

 possible for us not to regret a little the considerable time which 

 he devoted to this investigation, especially as it appears to us 

 very probable that it is not in the action of the atmosphere, but 

 much rather in that of the earth itself, or perhaps even in that 

 of the sun, that we must seek the cause of all the phenomena 

 presented by the magnetic needle. 



Lastly, a third point remains to be noticed, namely that which 

 relates to the investigation of the magnetic field and of what 

 Faraday denominates the lines of magnetic force. According 

 to him, as we have already had occasion to remark, there is no 

 such thing as action at a distance ; consequently the magnetic 

 field (that is to say, the space included between two approximated 

 magnetic poles, such as those of a horseshoe magnet) is a medium 

 from which, in every one of its points, forces emanate, the dis- 

 tribution and direction of which are indicated by the very regular 

 arrangement affected by fine iron-filings placed in this space. 

 The lines which he calls lines of magnetic force thus become 

 visible and even tangible. But they exist none the less even 

 when we cannot see them, and it is the displacements or modifi- 

 cations which they experience by the presence of a ponderable 

 body in the medium in which they occur that give rise to all the 

 remarkable effects of which the magnetic field is the scene. 

 Such is, in a few words, Faraday's view upon this particular 

 question. 



We pass in silence over a multitude of interesting details upon 

 diamagnetic polarity, upon the distinction to be set up between 



