114 
MR. W. GEOFFREY DUFFIELD ON THE 
The Supports for the Camera Girder. (Fig. 1, G and H.) 
This girder spans the room from wall to wall, each end resting in a cradle, which 
stands upon a strong metal bracket built into the wall. The cradles are of cast iron 
of the pattern shown in fig. 1, H, and are 18 inches long, 6 inches wide, and f- inch 
thick ; their sides are thickened at the top to provide sufficient metal for the two 
stout screws which serve to adjust the girder in a horizontal plane. Three set-screws 
with “ tommyholes ” passing upwards through the bases of the brackets support the 
cradles and regulate the height of the girder and the plane of its surface. 
The Cross-beam. (Fig. 1, C, and fig. 2.) 
This is a 4-inch tubular girder of wrought iron, as in Rowland’s original arrange¬ 
ment/"' but in this case constructed in three sections, of which the central portion is 
of slightly larger diameter than the ends^ so that a telescopic adjustment of its length 
is possible. The sliding parts can be firmly secured by set-screws and by two flexible 
metal straps. 
The method of attachment of the cross-beam to the grating and camera carriages, 
which is due to Sir Howard Grubb, obviates many of the defects of the earlier 
systems, which were not free from the constraint resulting from a too rigid 
connection. 
T 
rr^;-.-.-.-.1 
j 12 INCHES 
Fig. 2. The cross-beam ends. 
Lugs were brazed on to the two ends of the cross-beam, fig. 2, and parallelism was 
obtained by turning them relatively to one another within the central tube. A 
second and more delicate means for obviating any constraint is provided by the 
set-screws T, which pass through the U ends of the lugs; these have rounded ends, 
and are turned until all four rest evenly in the hemispherical sockets VV, fig. 5, in 
the carriage mounting, and they are then held firmly in position by means of lock¬ 
nuts. This feature, combined with the stable form of the carriages, secures freedom 
from tilting of the grating and from any change of focus due to the sagging or 
twisting of the cross-beam. 
* Ames, ‘Phil. Mag.’ (5), 27, 369 (1889). 
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