714 Scientific Proceedings, Royal Dublin Society. 
One end of this rectangular structure or box was permanently 
closed, and a short piece of brass tube made to slide through a hole 
in the end at the proper height for the slit. This brass tube was 
supplied with a boxwood flange fitting light-tight against the slit 
mounting, so that all the adjustments of the latter were outside 
the wooden rectangular box. 
The other end was closed by a sliding door. 
A light-tight connexion had now to be established viohieeey 
this wooden box and the camera at the other end of the girder, 
and inasmuch as the girder not only moved from one end of 
the tube to the other along the rail u, but at every new position 
on the rail made a different angle with it, it was impossible to 
accomplish this connexion by anything in the nature of a bellows. 
After much consideration the following method was decided on, 
and works admirably in practice :—On the iron tube of the girder 
was fixed, by means of wooden supports and clamps, a wedge- 
shaped rectangular tube of wood, a little wider than the grating at 
one end, and the width of the camera at the other, and about four 
inches deep. Part of this is shown in fig.1 as K. The end came 
to within about 13” inches from the face of the grating ec. 
Fig. 2 shows a section, which represents the construction for 
about one-half of its length from the grating end, the remainder 
being without the grooved slides (a). The tube is shown in plan 
in fig. 3. 
