Prof. Ch. V. Zcnger on a new Spectroscope. 445 



The new spectroscope, therefore, consists of a brass tube with 

 a slit at one end and closed at the other end (fig. 3). The slit 



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must be narrow and short, and the prism very near to it, turning 

 by a pinion (p) in its case. The mirror, inclined a certain 

 angle p to the axis of the tube, reflects from the other, closed end 

 the spectrum into a brass tube lateral to the former, containing 

 a small telescopic apparatus to receive sharp images of the spec- 

 trum reflected by the convex spherical mirror, and to magnifv 

 them to ten times the diameter. The mirror is adjusted in such 

 a way as to bring only a narrow zone of its middle part into 

 operation, the rest of the surface being protected by a cover with 

 a narrow slit in the direction of the rays emerging from the 

 prism, and parallel to the reflecting zone of the mirror. 



To increase the effect of the mirror, it can be brought nearer 

 to the closed end of the tube, and the side tube moved in the 

 same direction with it. Yet it seems more advisable to fix both 

 at such a distance as will give the greatest separation of the spec- 

 tral lines attainable without a great loss of light and a diminution 

 of the exactness of the image. 



London, October 17, 1873. 



