326 
POPULAR SCIENCE REVIEW. 
which are those corresponding with the formula 3R 3 P 2 0 8 + H 2 0, if in this 
formula R = Mn : Fe : Ca : Na = 6 : 1 : 1 : 1. A small amount of water was 
met with even in the most transparent specimens. If the water were not 
essential, the composition of the mineral would he somewhat analogous to 
that of triphyllite, containing sodium in place of lithium. 
A Titaniferous Chrysolite. — M. Damour has described a titaniferous 
chrysolite from Zermatt, Switzerland. ( Bull. Soc. Min. Franc., ii. 15.) It 
has a red colour similar to that of almandine garnet, and the specific 
gravity 3-27. Analysis shows it to consist of silicic acid 36T4 ; titanic 
acid 6-10 ; magnesia 4&-31 ; iron protoxide 6*89 ; manganese oxide 0*19 ; 
and loss by ignition 2*23. Total = 99-86. This gives almost exactly the 
required ratio 1 : 1 for bases to silicon. 
PHYSIOS. 
Rotation of the Plane of Polarization by Electro-Magnetism in a Vapour. 
MM. Kundt and Rontgen have communicated their results on this subject 
to the Munich Academy. They have proved the fact of such rotation, 
which Faraday failed in demonstrating, at least in the vapour of sulphide 
of carbon. This substance was chosen for experiment because it shows 
strong electro-magnetic rotation in the liquid state, and because its vapour 
has great tension, even at moderate temperatures. An iron tube, closed at 
the ends by thick glass plates, was enclosed in an outer tin tube through 
which steam at 100° Cent, could be passed. The outer tube was sur- 
rounded by six large coils of wire, containing 400 turns of thick wire each, 
through which a current from 64 large Bunsen elements was passed. Sul- 
phide of carbon vapour was heated as above described, and at the tempera- 
ture of boiling water the vapour became transparent. A beam of polarized 
light was passed through the tube, and analysed by Nicol’s prism. On the 
current being sent, a distinct brightening of the field was observed, which 
increased if, after rotating the prism afresh to darkness, the current was 
reversed. The rotation was in the direction of the positive current through 
the coils, and amounted to about half a degree. Sulphuric ether similarly 
treated gave no result. The authors of the paper are making apparatus by 
means of which to examine permanent gases and unsaturated vapours, with 
the special view of ascertaining whether oxygen rotates the plane of polari- 
zation in the same direction as other gases. Monsieur E. Bichat contributes 
a memoir to the “ Comptes Rendus ” of the Academy, in which he states 
that he has been following out a similar series of experiments since July 
1878, which give very different results from those noted above. He points 
out that the iron tube used by the German physicists very materially 
injures the completeness of the action. It is in reality a hollow electro- 
magnet ; whereas his tube being of brass allows the whole force of the 
current to expend itself on the contained vapour. In illustration of the 
difference, he passes a tube containing liquid bisulphide of carbon through 
the two poles of an electro-magnet, obtaining a rotation of 10° 30' ; but on 
using a single hollow core with the same current, no appreciable rotation is 
obtained. If the iron tube be thin, the action is not entirely annulled, but 
