on the glass. cover directly underneath the lens. This mark (BK! 
4) appears in the field of view crossing the card vertically. It has 
nearly the distinctness of the degrees because it is so near the card that 
the rays from it pass through the lens and are rendered nearly parallel. 
_ Manner of using the Microscopic compass.—As it is contained in 
a aie three and a half inches in diameter and one inch and ae 
ews it may be carried in the waistcoat pocket.. 
When the bearing of an object is to be taken, remove the ion! 
raise the sights, and holding the compass horizontally, by grasping the 
milled edge of the bottom by the thumb and fingers of one hand, 
move the eye up or down along the slitted sight till the object appears 
in the unsilvered part of the reflector. With the other hand incline 
the reflector backwards or forwards on its hinge till the graduated 
edge of the card is brought to the lower edge of the silvered part of 
the reflector and in apparent contact with the object. Turn the com- 
pass round till the vertical sight line crosses the object. The degree 
or degree and part which appears behind this line is the bearing, 
Some advantages might be obtained by using the instrument on a 
stand, but by a little practice the bearings may be taken very accu- 
rately by hand. I do not propose this as a substitute for the survey- 
or’s compass; but merely as an instrument exactly suited to ama- 
teurs and scientific travellers, to whom it is inconvenient or unpleas- 
ant to carry a back Joad of machinery, to take the bearing of an ob- 
ject. Ihave, for several years, been carrying on a trigonometrical 
survey of the beautiful valley of Cincinnati in which Lreside. This 
Ihave done for the recreation both physical and intellectual which 
-itaffords. It invites me to exercise in the open air and is the best 
antidyspeptic I have tried. J have managed the several points of the 
valley very much to my satisfaction with the sextant; but nothing 
rer so rel for va ieee seat the ravines, rivulets, and ridges of 
ass. I can take the angles with equal 
accuracy as with the il ’s and with ten times the convenience. 
Ttremains to explain the figures, and make some remarks on the 
construction. Fig. 1. represents the needle and graduated rim, a 
Vertical section of which is shown in Fig. 2. _N is the needle, which 
is one. twenty fifth of an inch thick, one eighth of an inch wide, and 
three inches long. AA are two pieces of brass, by means of which, 
the rim is fastened to the needle by screws at BB. The pieces : 
AA have holes at BB a little larger than the screws which pass 
_ through them, to allow the rim . = adjusted both to the’ center 
Vou. XXII.—No. 2 - 
. 
