SPECTRUM ANALYSTS. 735 



tained, the first colourless and apparently crystalline, the 

 second, under a high temperature, of the colour of the 

 blood-stain from which it was procured, and of the figured 

 pattern mentioned. 



Mr. Sorby's attention has been directed to obtain a defi- 

 nite method of qualitative analysis of "animal and vegetable 

 colouring matters," and of animal substances generally, by 

 means of the spectrum microscope. He has also so com- 

 bined the spectroscope with the binocular microscope as 

 to make it available for the purpose of distinguishing 

 minute portions of coloured minerals in thin sections of 

 rocks and meteorites. He employs an ordinary large 

 binocular microscope, with an object-glass of about three- 

 inches focal length, corrected for looking through glass an 

 inch thick ; the lenses being at the top, and as far as pos- 

 sible from the slit. This objective is placed at the focus, 

 and between it and the lenses, at a distance of about half 

 an inch from them, is a compound prism, composed of a 

 rectangular prism of flint-glass and two of crown-glass, of 

 about 61, one at each end. This arrangement gives direct 

 vision and a spectrum of a suitable size for these inquiries, 

 since a wide dispersion often produces indistinctness of 

 the absorption bands. That we may have the opportunity 

 of comparing two spectra side by side, a small rectangular 

 prism is fixed over half the slit, and with the acute angle 

 parallel to it and passing beyond it. 1 



" This gives an admirable result, the only defect being 

 that, when the spectra are in focus, their line of junction 

 is some distance within it ; and therefore to correct this 

 employ a cylindrical lens of about two feet focal length, 

 with its axis in the line of the slit, which can easily be 

 fixed at such a distance between the slit and the prisms 

 as to bring the spectra and their line of contact to the 

 same focus. In front of the slit, close to the small rectan- 

 gular prism., is a stop with a circular opening, to shut out 

 lateral light, and a small achromatic lens of about half 

 an inch focal length, which gives a better field, and 

 counteracts the effect of the concave surface of the liquid 

 in the tubes used in the experiments, if they are not 



(1) Mr. Sorby's prisms and thei-r arrangement have been entrusted to Mr 

 Browning's skilful hands, who is prepared to adapt them to any microscope. 



