634 
WELDON RANGE FINDER. 
Major Richardson’s description of the instrument shown in Fig. 6, 
Fig. 6. 
is also evidently incorrect. Instead of an inclination of 88° 34' 3" for 
the mirrors, it should be half that, or 44° 17' 1"*5, to give a deviation 
of 88° 34' 3". The angle H G I need Fig. 9. 
be only about 45° instead of a little 
over 89°. 
Fig. 9 shows, in plan, a proposed 
instrument, in which the mirrors can 
be adjusted at will for an angle of 
44° 17' 1"*5 or of 45°, so as to give 
a deviation of 88° 34' 3" or of 90°. 
This is for use in place of the two 
prisms described above. It is partly 
suggested by the Watkins (see Ord. 
Note 116) and partly by the Weldon 
range-finder. It is simpler than the 
former and not so limited in use as the 
latter since it permits the employment 
of two lengths of base. 
