78 Intelligence and Miscellaneous Articles. 
From the researches of M. Becquerel it appears, that under the 
combined influence of heat and pressure, slow actions acquire new 
activity and produce interesting effects in a physico-chemical and 
geological point of view.—Comptes Rendus, May 11, 1857, p. 9388. 
NOTE ON THE OPTICAL PROPERTIES OF MAGNETIC BODIES, 
BY M. VERDET. 
In a note read some time ago before the Academy of Sciences*, 
the author made known some experiments showing that under the 
influence of magnetism the salts of iron exert an action upon polarized 
light opposite to that of water, glass, sulphuret of carbon and some 
other transparent substances. On studying the compounds of the 
other magnetic metals, he has found that a certain number of them 
act upon light in the same way as the compounds of iron. 
He gave the name of magnetic rotatory power to the property of 
rotating the plane of polarization temporarily developed by magnetism 
in transparent substances. The magnetic rotatory power of most 
transparent substances he called direct, and that of the salts of iron, 
inverse. He now proposes to substitute for these terms the expres- 
sions positive and negative, which indicate the direction of the rota- 
tion. Water, sulphuret of carbon, glass and the other transparent 
substances of which the rotatory power is positive, rotate the planes 
of polarization in the direction in which positive electricity traverses 
the conducting wire of the electro-magnet; the salts of iron rotate 
it in the direction of movement of negative electricity. 
The magnetic metals of which the author has investigated the 
transparent compounds, are iron, nickel, cobalt, manganese, chromium, 
titanium, and cerium. All these metals are attracted by electro- 
magnets, and form compounds endowed with the same property. 
There are other metals, such as platinum and its analogues, which 
appear to be magnetic, but all the compounds of which are diamag- 
netic; the magnetic character of these metals is therefore not 
absolutely certain}. 
Tron.—Protosalts of iron are endowed with a negative magnetic 
rotatory power, evidenced by the weakness of the action which the 
aqueous solutions of these salts exert upon polarized light. This 
action is always weaker than would be that of the water contained 
in the solution, but in the same direction, and the author has not 
met with any protosalt of iron possessing a negative power sufficient 
to destroy entirely the positive power of the water. To make quite 
sure of this phenomenon, the author prepared solutions of sulphate 
of iron of different degrees of concentration, and found that the 
rotations produced agreed exactly with the hypothesis, that these 
solutions are mixtures of two bodies endowed with opposite rotatory 
powers}. 
* See Phil. Mag. S. 4. vol. xii. p. 483. 
+ On the distinction between the magnetic and diamagnetic metals, see 
the 21st Series of ‘Experimental Researches in Electricity,’ by Professor 
Faraday. ; 
t The experiments relating to these variously concentrated solutions 
presented a remarkable peculiarity. Considering them as formed of water 
