324 Grusp—A New Collimating- Telescope Gun-Sight for large and small Ordnance. 
would be of course equally impracticable for obvious reasons, but it is instanced 
to show that a beam of light has the necessary qualifications for our purposes. 
Now, the sight which forms the subject of this Paper attains a similar result, 
not by projecting an actual spot of light or an image on the object, but by 
projecting, what is called in optical language, a ‘“ virtual” image upon it. 
DESCRIPTION. 
The original conception of this sight is represented in fig. 1. The object to 
be aimed at is viewed through a short piece of tube (AB) preferably square, 
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open at both ends, in which is mounted, at an angle of 45°, a plate or plates 
of parallel glass, similar to those used in sextants. 
