226 On the Mounting of the Large Rowland's Spectrometer. 



as the sliding doors referred to as moving in the grooves A, A 

 in fig. 1 could not come beyond the points of intersection of 

 the tube K with their plane (namely I, I in fig. 3), and 

 inasmuch also as the lower grooved piece (A, fig. 1) had to 

 be at sufficient distance below T 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 K, 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 

 removed in fig. 1, so as to show the tube and tie-rods. 



Fig.2. 



Camera 



The outer end of the bag, or the end nearer the camera, 

 was closed up, and the other came well within the plane of 

 A A, 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 K. The camera is connected to 



