PHYSICS. 371 



Lommel has described a new polarizing apparatus, in which two plates 

 of magnesium platinocyanide, cut perpendicularly to the optic axis, are 

 used as polarizer and analyzer, as in the tourmaline pincettes. In the 

 tourmaline, however, the ordinary ray is the one that is absorbed, while 

 here it is the extraordinary ray; hence the tourmaline is cut parallel to 

 the optic axis and the platiuocyanide perpeudicular to it. The new ap- 

 paratus transmits abluelight, which, when the angleof incidence exceeds 

 2<^, is perfectly polarized iu the plane of incidence. ( Wied. Ann., 1881, 

 II, xiii, 347; Mature, July, 1881, xxiv, 291.) 



Bertin has improved the tourmaliue pincette by applying to it a part 

 of the lenses of a polarizing microscope. The ordinary instrument can 

 be used with onl}^ a limited number of crystals, by reason of the small- 

 ness of its field ; but the new one shows well the fringes only 2 milli- 

 meters in diameter and ^ millimeter in thickness. All uniaxial crystals 

 give fringes in it, and biaxial crystals can be observed when, as in the 

 case of calamine, their axes are 75° 20' apart. {J. Phys., March, 1881, 

 X, 116.) 



Whitwell has described a simple polarization experiment. If a plate 

 of ice be broken off and held between the sky and a pool of water its 

 reflected image will show color. The incident rays should come from 

 the sky, about 90° from the sun, and reflection should take place at the 

 polarizing angle for water. {Nature, January, 1881, xxiii, 2G8.) 



Sorrensen has also observed some polarization x^henomena with ice 

 and water. The ice on a window i)ane had melted and the water formed 

 a pool at the bottom, in which various bright and beautiful colors ap- 

 peared. On examination they proved to be the grotesque images of the 

 frost-flowers on the pane reflected iu the water. The daylight itself 

 was strongly polarized, which was attributed to the presence of a light 

 mist of ice particles reflecting the sunlight. The temperature of the 

 external air was about 12°. (Nature, March, 1881, xxiii, 442.) 



Henri Becquerel has investigated elaborately the rotatory polariza- 

 tion of gases. He concludes (1) that the plane of polarization is rotated 

 in gases under magnetic influence; (2) that the rotation is inversely as 

 the square of the wave-length of the light used ; (3) that the rotatory 

 power can be compared to liquid carbon disnlphide, and so to other 

 liquids and gases, and (4) that oxygen shows anomalies, connected 

 probably with its magnetic properties. {Ann. Chim. Phys., November, 

 1880, V. xxi, 289; Am. J. ScL, February, 1881, III, xxi, 139.) 



Becquerel has since extended the above results, and now shows that 

 even the earth's magnetism is strong enough to rotate the polarized ray. 

 He finds that- the rays D traversing horizontally a column of carbon 

 disulphide one meter long undergo at the temperature 0° C, and at 

 Paris, a magnetic rotation of 0.8G97'. (C. B., September, 1881, xciii, p. 

 4-Sl; Am. J. ScL, December, 1881, III, xxii, 484.) 



