Apenry & Carson—The Rowland Spectrometer, R.U. I, 715 
The opening (B) was in that side of the tube nearest the rail, 
and was necessary when the camera was close up to the slit; since 
the light from the slit would otherwise be cut off from the grating 
by the angle of the tube coming between them, as shown in fig. 3 
in plan. 
An arrangement for wholly or partially closing this opening 
at will was provided, in the shape of a door sliding in the 
grooves AA. 
In order to close up the space below the tube x, inasmuch as 
the sliding doors referred to as moving in the grooves Aa in fig. 1 
could not come beyond the points of intersection of the tube k 
with their plane—namely, 1 in fig. 3—and inasmuch also as the 
lower grooved piece (A, fig. 1) had to be at sufficient distance below 
to clear the lowest point of the tie-rod r, the simplest way that 
could be thought of by the authors was to suspend a loose bag or 
tube of felt cloth from the lower edges of the sides of x, letting it 
hang down and enclose the girder and its tie-rods. 
This is shown at c in fig. 2, but is supposed to have been re- 
moved in fig. 1, so as to show the tube and tie-rods. 
The outer end of the bag, or the end nearer the camera, was 
closed up, and the other came well within the plane of aa, 
fig. 1. 
This was found to answer admirably, and by the aid of a cloth 
thrown across K,and loosely tucked in against a on the top, and the 
sliding doors and the felt bag at the sides, no difficulty has been 
experienced in obtaining a perfectly light-tight joint in all positions 
of x. The camera is connected to the other end of x by a few 
inches of bellows, which allows for the focussing adjustment. 
