PHYSICS NINETEENTH CENT.SPECTROSCOPY. 487 



Bunsen gas-burner a. The apparatus included, as will be seen, an 

 arrangement for turning the prism so that the lines of the spectra might 

 be identified by the angular position of the prism when these lines 

 were brought into coincidence with cross-wires in the telescope. But 

 greatly improved forms of spectroscopes were soon afterwards contrived. 

 For example, from the face of the prism next the telescope the image 

 of a graduated scale was reflected into the telescope, and being seen 

 simultaneously with the spectra, the graduation at which the lines ap- 

 peared could be noted, and they could therefore be identified by their 

 position. The box was dispensed with, because a black cloth thrown 

 over the prism and the inner ends of the tubes cut off all extraneous 



FIG. 223. SPECTROSCOPE WITH ONE PRISM. 



rays. Fig. 223 shows the form of single-prism chemical spectroscope 

 now constructed by Mr. Browning. The slit is on the left, the tele- 

 scope on the right. The prism is supported on a little stage fixed in 

 the centre of a horizontal disc, about whose centre moves an arm 

 carrying the telescope. The limb of this disc is graduated, and the 

 movable arm carries a vernier (page 212). Any line of a spectrum is 

 identified by the angular reading when the line coincides with the 

 cross-wires in the eye-piece of the telescope. In the front of the slit 

 a small prism is so mounted that it can be either made to cover half 

 the length of the slit, or can be turned aside altogether. The object 

 of this arrangement is to reflect, when required, rays from a second 

 Bunsen's burner or other source of light placed laterally, so that two 

 spectra may be viewed side by side, and their lines compared. 



In the hands of Bunsen the new method of spectral analysis very 

 soon led to some striking results, for in 1860 he had added by its 

 means two new metals to the list of chemical elements. In examining 

 spectroscopically the salts contained in the waters of a mineral spring 



