THE SPECTROGRAPH. 



169 



APPARATUS. 



THE SPECTROGRAPH. 



The apparatus was designed by one* of us in his previous study of the 

 absorption spectra of the aniline dyes. Since 

 reference to other descriptions of the spectro- 

 graph may not be convenient, a brief account of 

 its chief characteristics will be given below. The 

 essential parts of a vertical section of the spec- 

 trograph are outlined in their exact relative pro- 

 portions in fig. 64, which is one-fifteenth of the 

 natural size. This may be described as follows. 

 In the first place, each element of the system was 

 adjustable in every respect. Light from a Nernst 

 filament N was focused by the concave speculum 

 mirror R, on the slit S, whence it continued to 

 the grating G, from which a portion of it was dis- 

 persed in the direction of the sensitized film F. 

 The adjustable support of the mir- 

 ror was rigidly attached to the main 

 body of the spectrograph. The dis- 

 tances from the middle of the slit to 

 the centers of the mirror and grating 

 were, respectively, about 89.5 and 

 97.1 cm. The electrodes E were so 

 located above the slit as not to inter- 

 fere with the passage of light from 

 the reflector to the slit. No lenses or 

 other reflectors were used. The mi- 

 crometer head at M indicated the 

 separation of the slit- jaws. Q and 

 Q' denote a screen system, such that 

 when Q was vertical the passage of 

 light from the grating to the camera 

 was not interfered with; whereas 

 when Q was horizontal only ultra- 

 violet light of shorter wave-lengths 

 than 0.4// could reach the photo- 

 graphic film. PP is a horizontal 

 platform with a scale along its front 

 edge. By sliding horizontal opaque 



screens of various widths along this 



FIG. 04. 



*Uhler and Wood: Atlas of Absorption Spectra, Publication No. 69, Carnegie Institu- 

 tion of Washington. (In press.) 



