326 Grusp—A New Collimating-Telescope Gun-Sight for large and small Ordnance. 
upon an invisible, imponderable, and inflexible prolongation of the barrel, thus 
obviating the necessity for any back-sight, for any motion of the eye makes no 
perceptible difference in the coincidence of this “virtual” image and the object. 
As the form of the sight above described would evidently be highly objectionable 
in most eases, the instrument was modified to the form shown in fig. 2, which, it 
will be observed, is exactly on the same principle, except that instead of mounting 
the collimating tube carrying the diphragm and object-glass, at right angles to, 
and above, the sighting tube, this collimating tube is mounted underneath the 
sighting tube and parallel to it, the rays being bent by a reflector or prism, 
rendering the instrument of a more practical form. 
It will be noticed, in both this instrument and that represented by fig. 1, that 
three plates of glass are shown superposed upon one another for reflecting the image 
of the device on the diaphragm into the eye:—The object of this is to intensify 
the brilliancy of the reflected image without sensibly diminishing the apparent 
brilliancy of the object aimed it. Later on, however, it was found that a more 
practical plan of increasing this brilliancy was to use one single piece of glass, 
and coat this with a semi-transparent and highly reflective film. A long series 
of experiments carried out by Professor J. Emerson Reynolds, F.R.S., and 
Mr. G. Rudolf Grubb, B.A.I., resulted in a modification of a process invented by 
the former by which the desired film was obtained. 
r | ee aoa 
This portion silvered 
on anside surpace 
loie, & 
Fig. 3 shows a further modification, and the most generally favoured form of 
instrument at the present time, in which it will be seen that the diaphragm is 
