PHYSICS. 489 



of the rings produced coincidiug with the edge of the striated surface, 

 it is observed that the diameter of the rings is different on the polished 

 ajid the striated i)ortious. These phenomena are inexplicable in the 

 present state of optical science. ( Wied. Ann., V, xiii, p. 133; J. Phi,s., 

 January, II, i, p. 50.) 



Loramel some time ago showed that a plate of magnesium platino- 

 cyauide perpendicular to the axis polarizes completely in the plane of 

 incidence blue rays which fall upon it at an incident angle greater than 

 2°. He has now constructed a polariscope with. plates of this salt, anal- 

 ogous to the tourmaline pincette; but a layer of copper sulphate must 

 be i)laced before the polarizer so that blue rays only shall pass. For 

 dichroic substances with superficial colors, polarization by refraction is 

 not due to absorption, but results from the fact that the light rellected 

 from such a surface is completely polarized in a plane perpendicular to 

 the plane of incidence. Hence the transmitted rays are polarized in 

 this plane. ( Wied. Ann., V, xiii, p. 347 ; J. Phys., April, II, i, p. 199.) 



Govi has proposed to rotate the analyzing nicol prism of a projection 

 apparatus, to which a direct-vision prism is attached for the purpose of 

 determining the direction of rotation of the polarized ray produced by 

 a plate of quartz placed between the nicols. The spectrum will be cir- 

 cular, the red being at the center and the violet at the circumference. 

 When the quartz plate is interposed, two black archimedcan spirals 

 will appear, moving toward or from the center, according to the direc- 

 tion of rotation of the quartz. {J. Fhys., August, II, i, p. 372.) 



The saccharimeter of Laurent has hitherto required monochromatic 

 light. A new modification of this iustrument, using ordinary light, has 

 recently been introduced by the maker, in which the rotation of the 

 sugar solution is balanced by a quartz compensator, as in the Soleil 

 instrument. Dufet has given the theory of the new instrument, and 

 shows that this modification restricts the use of the instrument to solu- 

 tions of sugar, the law of rotation of which is sensibly the same as that 

 of quartz. {Comptes Bendus, xciv, 442; J. Phys., December, II, i, 552.) 



ELECTRICITY. 



1. Magnetism. 



Eaton has investigated the conditions of maximum magnetization of 

 diamagnetic and feebly i)aramagnetic bodies, using an experimental 

 method analogous to that of G. Wiedemann. The results obtained with 

 ferric chloride show that the magnetism of a solution of this salt is ex- 

 actly proportional to the magnetizing force; hence a maximum of mag- 

 netization does not exist for feebly magnetic substances, at least up to 

 the limit given by seven Bunseu cells. With diamagnetic bodies, the 

 author comes to the same conclusion. ( Wied. Ann.,Y, xv, 225 ; J. Phys., 

 July, II, I, p. 333.) 



Schuhmeister has determined several magnetic and diamagnetic con- 



