THE BOX SEXTANT, 
21 
the telescope, by drawing the slide , L, over the hole from which the 
telescope has been removed. 
Adjustments :—Having set the index at zero (0°) on the arc, select some 
object that is sharply defined and perpendicular, as far distant as possible, 
to be seen clearly; then, holding the instrument in a horizontal position, 
look at this object through the eye-hole, and, if the reflected image coincides 
with the object seen directly, the adjustment is so far correct. Then hold 
the instrument the contrary way, or vertical, look at some object that is 
level, and if the reflected and real objects are seen in a straight line this 
adjustment is also correct; but when this is not the case the adjustment 
must be made by taking out the key, H, placing it in one of the keyholes, 
M, either on the top or side of the instrument, and turning it gently 
until the reflected image of the object coincides with the object seen 
directly. If the reflected image requires moving up or down, the key 
must be inserted on the top of the instrument, but when it has to be 
moved to the right or left the key must be inserted at the side. 
These adjustments can be made, when no available objects, such as 
those mentioned, are in sight, by the sun, using a suitable shade. Set the 
index to zero, and move it until the reflected and direct images coincide; 
if the index then points to zero (0°) the instrument is in adjustment, if 
pot, make the eojncidenee with the key as above described, A bright 
