USE OF THE MICKO-SPECTKOSCOPE 



327 



characteristic absorption bands represented (after Professor Stokes) 

 in fig. 273. 1 



For the study of coloured liquids in test-tubes or small cells, the 

 binocular spectrum microscope, described by Dr. Sorby in the * Pro- 

 ceedings of the Royal Society,' No. 92, 1867, p. 33, is extremely 

 convenient. 



Tlie spectral ocular by Zeiss is another and a very perfect form of 

 the micro-spectroscope. This is an opinion expressed by Dr. Sorby 

 and other experts, and it is manifest in the character of the in- 

 strument. Fig. 274 represents a sectional view of the instrument. 

 It will be seen that the lower part is an ordinary eye-piece with its 

 two lenses, but in place of the ordinary diaphragm there is a slit 

 adjustable in length and breadth, shown in fig. 275. By studying 

 this figure the method of adjustment with two screws, F and H, 

 and the projecting lever, whi'ch. carries a reflecting prism, can be 



FK;. 274. 



FIG. 275. 



readily understood. The upper part of the instrument swings 

 about the pivot, K, so that by opening the slit the eye-piece can be 

 used for focussing an object, the slit being the diaphragm. The 

 upper portion contains the prisms, and also a scale in the tube, N, 

 which is illuminated by the mirror, 0. The image of the scale is 

 reflected from the upper surface of the last prism to the eye, and 

 when properly adjusted gives the wave-length of the light in any 

 part of the spectrum. There is also a supplementary stage, not 

 shown in the figure, upon which a specimen can be placed, and its 

 light thrown up through the slit by reflection from the prism on the 

 lever shown in fig. 274, alongside of the light from the object on the 

 stage of the microscope, thus enabling the spectra from the two 

 sources to be directly compared. 



1 For further information on ' The Spectrum Method of Detecting Blood,' see an 

 important paper by Dr. Sorby in Monthly Microsc. Journ. vol. vi. 1871, p. 9. 



