Fig, ;f 
1 he telescope of the interferometer is mounted on a mahogany base 44 centims. by 
38 centims., of the same tliickness as the main base, to wliicb it is attachable bv three 
pegs fitting in holes in the fi'ont edge of the plinth, the outer moulding of 'which is 
here detachal)le to admit it. The smaller base is then continuous with the main base, 
and brings tlie telescope up (piite close to the to|) prism of the refracting train, about 
5 centims. being tlie l)est distance for clear focussing of the silvered reference ring- 
carried at the centre of the large glass disc of tlie interference apparatus. 
The JTocks and Knife-Edges for supporting the Plate. 
Somewhat to the left and front of the centre of the iron liasal slab an enamelled 
iron lilock is fixed (n in the accompanying vertical section, fig. 3), with one end 
146 
DR. A. E. ri. TUTTON OX THE ELASHOMETER, 
of the interferometer, are mounted on a rigid enamelled iron slab, rectano-ular in its 
front portion, the front edge lieing 71 centims. long and tlie sides 37-5 centims. The 
slab is continued backwards in the form of a broad arm for a further 22 centims., 
somewhat to the left of the centre, for the support of the back foot of the pedestal. 
The iron base is in turn mounted on a rectangular mahogany base, on the plinth of 
winch fits a glass case with strong mahogany framework, to cover the whole apparatus 
when not in use. One end of the case is removable, and the latter can then be 
readily drawn off, the liottom of the frame being covered with cloth to facilitate the 
sliding. 
