498 THE SPECTROSCOPE. 



as the much broader images of the whole flame, and 

 flame and slit may therefore be brought much nearer to 

 the prism, so that we may use our right hand for intro- 

 ducing the platinum wire into the flame without re- 

 moving our eye from the prism. The box which con- 

 tains the prism has besides the slit, which is cut into one 

 side, only one other aperture where the eye is applied ; 

 hence no light can enter but that which passes through 

 the slit, "and the apparatus may therefore be used in 

 daylight if a blackened sheet of pasteboard is placed 

 behind the flame. 



A very simple spectroscope, for which our disulphide of carbon 

 prism may be employed, is shown in fig. 280. A represents its 

 exterior, and B its interior, when the lid of the box is removed. 

 In (7, V, and E, a more elegant form of the same apparatus is shown, 

 which may be provided with very little additional expenditure. 



The box k k of cardboard has four vertical sides, of which one 

 of the shorter sides, in the figure the one on the left, is inclined to 

 the two longer sides, the other short side being at right angles to 

 them. The slanting side contains the aperture o for the eye ; in the 

 opposite side a rectangle is cut out of the cardboard, 2 cm high and 

 l cm broad, and closed by a plate of glass, g. A cover, d d, with a 

 rim which reaches about l cm over the sides of the box, must fit easily, 

 but closely upon it. Inside the cardboard is blackened (see p. 495), 

 and also the outside of the slanting side ; the other portions of the 

 exterior may be covered with some coloured paper, to give to the 

 whole a better appearance. 



Obtain from a glazier, or cut with pastille, a rectangular piece of 

 plate or window glass, 4 cm long and 3 cm wide ; smooth en the edges 

 upon the grindstone, and cover one side with tinfoil. This is done 

 by laying a little starch-paste upon one side of the glass, placing 

 upon it a piece of tinfoil of the size of the glass, and pressing the 

 tinfoil with a few fingers of the left hand upon it, so as to prevent 

 it from sliding, while the soft tip of the right forefinger is drawn 

 from the centre to the edge of the tinfoil, in all directions, so as to 

 make the tinfoil adhere smoothly everywhere to the glass, and to 

 squeeze out nearly the whole of the paste at the edge ; only a trace 

 of the starch should remain, otherwise the tinfoil will not adhere 

 afterwards to the glass. In the tinfoil a cut is made 2 cm long, by 



