602 SCIENTIFIC RECORD FOR 1883. 



ceeded only by the Thollon spectroscope. But in this instrument the 

 loss of light from the absorptions and reflections is far less. (G. R., 

 April, 18S3, xcvi, 1039.) 



Crova has described an improved form of spectrophotometer which 

 consists essentially of a direct vision spectroscope having an adjustable 

 slit in the eye-piece and a double rectangular prism covering one-half 

 the ordinary slit. One beam passes to the prism directly; the other 

 enters from a perpendicular direction passing into the collimator through 

 the total reflection prisms. In the path of this rectangular beam two 

 nicols are placed with a graduated circle by the position of which the 

 movable one may be read off. The two lights to be compared are placed 

 at equal distances, the brighter in front of the nicols, dud the analyzer is 

 turned until the intensity is the same in any given portion of the two 

 superposed spectra. (Ann. Chim. Phys., August, 1883, V, xxix, 556.) 



It is often desirable to place the slit of a spectroscope at an angle 

 with the axis of the prism. Garbe has shown that this may be done 

 by placing, immediately behind the slit an ordinary reversing prism, with 

 its axis in that of the collimator. Under these circumstances the vir- 

 tual image of the slit will not be displaced by its rotation. The device 

 is similar to that used by Thollon. (J. Phys., July, 1883, II, u, 318; 

 C. R., March, 1883, xcvi, 836.) 



Cornu has suggested a new form of spectroscope, which gives a high 

 dispersion. A right-angled prism throws the light from the slit along 

 the axis of the collimating lens, whence it passes through the prism and 

 is incident upon a reflecting surface at 45°, by which it is thrown ver- 

 tically upward upon a second mirror at 45°, which returns it to the 

 prism. After traversing this a second time it is incident normally upon 

 a mirror, which returns it over its course to the eye-piece of the col- 

 limator. The ray thus passes four times through the prism; and since 

 this is of carbon disulphide the dispersion obtained is very consider- 

 able. (J. Phys., February, 1883, II, n, 53.) 



Eohrbach has produced a liquid possessing extraordinary high refract- 

 ive and dispersive power. One hundred parts of barium iodide and 130 

 parts of mercuric iodide are heated in a test-tube with 20 cc of dis- 

 tilled water, the whole placed in an oil bath at 150° to 200° C, and well 

 stirred. A liquid double iodide of mercury and barium is formed, 

 which is poured into a shallow porcelain dish and evaporated down 

 until its density is so great that an epidote crystal no longer sinks in it. 

 Even topaz will float in it when cold. It is then filtered through glass 

 wool. It has a density of 3.575-3.588, boils at about 145°, and is yellow 

 in color. Its refractive index is 1.7755 for the C line and 1.8265 for the 

 E line of the spectrum. For the two D lines of sodium are 1.7931 and 

 1.7933, respectively. When a hollow prism of 60° filled with this liquid 

 is used in the spectroscope the separation of the D lines is almost ex- 

 actly 2'. (Nature, November, 1883, xxix, 63; Wied. Ann., xvn, 169; 

 Am. J. Sci., November, 1883, III, xxvi, 406.) 



