298 
light tight. At A an attachment is arranged to hold a ground glass for focus- 
ing purposes, and a common camera plate holder for making the exposures. 
The camera tube is mounted on a common prism spectrometer in place of 
the telescope as shown in Fig 2. The collimator slit, prism, and light source 
to be studied are adjusted in the usual way. When all adjustments, together 
| 
Fig. 2. 
with focusing the objective lense of the camera, have been made, a clearly 
defined spectrum image, including the Fraunhofer lines, may be seen upon the 
eround glass. In the usual procedure a plate holder containing an unexposed 
plate may be substituted for the ground glass and the exposure made. 
The instrument constructed in our laboratory has proven to be very 
successful for student work. 
