EFFECT OF PRESSURE UPON ARC SPECTRA. 
113 
adopted a heavy carriage with four wheels, two of which were grooved to run on a 
rail, while a parallel wooden flat-topped beam served to support the other pair. 
The Supports for the Grating Girder. (Fig. 1, F.) 
Three cast-iron brackets are braced to the wall, and through their bases pass strong 
set-screws to afford a means for adjusting the plane of the girder and its height above 
the floor. 
The Girder for the Camera Carriage. (Fig. 1, B.) 
This is a heavy cast-iron girder of hollow rectangular section, 23 feet long, 
18 inches high, and 8 inches wide, whose upper edges have been planed to form rails 
of the same shape and size as those of the grating girder. 
,10 
Fig. 1. General view of the mounting. 
J 20 FEET 
A. Grating girder. 
B. Camera girder. 
C. Cross-beam. 
D. Carriages. 
VOL. CCVIII.-A. 
F. Bracket for grating girder. 
G. Bracket for camera girder 
(built into the wall). 
H. Cradle for camera girder. 
Q 
