SrECTRO-MICROSCOPY. 119 



on the film. This illuminator is employed in the position 

 of the achromatic condenser, and a disc of slightly coloured 

 neutral tint-glass placed below the bottom lens increases 

 the purity of the light, and gives greater distinctness to 

 objects. The effect of this diffusing film is sometimes 

 enhanced by condensing light down on the object from 

 above as well as from below." 



An important improvement has been effected in Nachet's 

 binocular by Professor Smith, of Kenyon College, U.S. 

 It consists in the adaptation of Nachet's set of prisms for 

 use as eye-pieces, with any monocular instrument. The 

 prisms being mounted in a light material, vulcanite, are 

 made to fit into the microscope body and take the place 

 of the ordinary eye-piece. The image transmitted by the 

 objective is brought to a focus on the face of the first 

 equilateral triangular prism by the intervention of an 

 erector eye-piece placed beneath it. The second set of 

 prisms are by a rack-and-pinion movement adjusted to 

 suit any visual angle; while the illumination of both 

 fields is quite perfect, even with high powers. 



SPECTRO-MICROSCOPY. 



The application of the spectroscope to the microscope is 

 one of the most beautiful additions the instrument has lately 

 received. The honour of the invention appears to belong 

 to H. C. Sorby, F.RS., whose first experiments were made 

 with a simple triangular prism, arranged and fixed below 

 the stage, so that a minute spectrum of any transparent 

 object might be readily examined, when placed in position 

 immediately before the slit. Shortly after the publication 

 of Mr. Sorby's paper, Mr. Huggins proposed to adapt a 

 direct vision spectroscope to the eye-piece, and so enable 

 us to view the spectra of opaque as well as transparent 

 objects. The exact form of prism finally adopted, and 

 now in general use, is that known as the Sorby-Erowning 

 Spectroscope. 



The first spectroscope made by Mr. Browning (Minories) 

 is represented in fig. 69. A prism is placed at p, which is 

 enclosed in a box, so as to give a black field, by excluding 



