sights may be considered as a part of the cylinder of which the box 
ismade. The sight K S which is to be used next to the eye, is made 
precisely as in the common compass, having several holes placed ver- 
tically, and these connected by a slit ounitahiaiealh of an inch wide. 
(Fig. 3.) The opposite sight V J is slitted and perforated i in a simi- 
lar manner from V to Q chiefly for the purpose of reversing for ad- 
justment. . Its main use however is independent of theseelits, it is in- 
tended to support at its top an inclinable reflector (M), the inclina- 
tion being directly towards the first sight KS; and immediately be- 
low the reflector, a single lens or microscope (L), placed horizontal- 
ly one inch above the card and having an inch focus. In these two 
parts, the Jens and the reflector, lies the peculiarity of the instru- 
ment. 
Every philosophical reader is now enabled to understand the use 
of the instrument. The rays of light passing ree, upward 
from any point of the card to the lens, pass through it and emerge 
parallel above it, where meeting with the reflector (M) inclined to an 
angle of forty-five degrees, they are reflected horizontally through the 
Opposite sight at(O). The eye atthe sight (O) would of course see 
the card in the direction in which the rays were last received ; that is, 
in a horizontal direction. As the rays would be rendered spe 
ard would appear at a great distance and magnified. 
The card thus reflected would appear in a vertical position, in 
the position of a full moon just risen, with that point which is really 
farthest from the eye as the lowest point in the reflected image. It 
should be remarked that the whole of the card is not seen at once in the 
‘Yeflector, but only about ten degrees of the lowest part of it. (Fig. 4.) 
The silvering of the reflector being removed from the lower half, (from 
M towards J) any distant lect can be seen through the opening 
while the card is reflected from the upper part, and by inclining the 
reflector on the hinge (J) the graduated edge of the reflected card 
fan always be brought to visual contact with the object whose bear- 
ing is at once read, as it were, on itself. The rays of light coming 
from a distant point are nearly parallel, and those coming from the 
oe: re made so by passing through the convex lens; the eonse- 
ce is that both the degrees on the card, and the ages are seen 
clear as if equally distant. This would not be the case if 
: the card were reflected without the interposition of the lens, — The 
s on the card and the object would then be:k in the 
‘one object within three inches of the eye and wi — 
* 
