224 Dr. W. E. Adeney and Mr. J. Carson on the Mounting of 



For various reasons we decided not to erect the spectro- 

 meter in a dark room, but determined rather to set it up in a 

 room open to day- and sunlight, and to endeavour to devise 

 the light-tight connexions between the working parts of the 

 instrument which then become necessary for photographic, 

 as well as for eye, observations. 



A raised floor, 30 feet by 30 feet and about 9 feet high, was 

 built at one end of the Physical Laboratory of the University, 

 the floor being supported on steel girders, the ends of which 

 were built into two opposite side-walls of the laboratory, while 

 the central portions were supported by steel columns resting 

 on concrete foundations. 



The spectrometer was mounted on this raised floor in the 

 following manner : — 



M represents a cast-iron standard. 



B „ the beam 12 in. by 3 in. 



S „ the saddle. 



H „ the rail. 



E „ sheeting § in. cedar wood. 



C „ framed top fastened to E and supported by brackets. The 



panels in this are represented by movable lids (D). 



A, A are pieces secured one to B and the other to C, and grooved for 

 the reception of sliding doors, each about 2 feet wide, by means 

 of a series of which the side of the rectangular box could be closed 

 in from either end, making the whole completely light-tight. This 

 construction was necessary, inasmuch as the girder passed out 

 through this side, and at a varying angle, and different position, 

 with every movement of the grating-carriage along H, and with 

 the corresponding movement of the camera along the other rail H'. 



