Reflective Goniometer. - ; 77 
the degrees upon BB; and for the better concentration of the visual 
rays a small knee K, is made to fit upon thie line of O on the ver- 
nier at the angle of vision K. 
The plane II (oft maple or any light cakiwed wood) i is made to fit 
the inner part of A; both surfaces I and A being in the same plane 
anteriorly, one inch in depth and seventeen inches in diameter. It 
revolves upon the iron axis Z, and has a small brass head piece E, 
attached to it (and-revolving with it) from the center, p, of which is 
a pin projecting three fourths of inch from its surface, upon which 
the crystalline form that we wish to inspect is adjusted and fastened. 
A semi-circular band of brass BB, three fourths of an inch wide is 
fastened to the upper edge of II, graduated in degrees correspond- 
ing to the minutes upon the vernier D. ‘The small rollers a, a, are 
of iron one fourth of an inch in diameter, secured in the inner plane 
s,s, of A, for the more easy and true moving of IJ. And to hold 
_the revolving plane II, immovably upon its arbor Z; and thereby to 
prevent BB, from slipping from its place, (after adjusting it by ob- 
servation,) before we read the angle off; we have a brass clamp 
C, screwed fast upon the edge of I, and pressing upon a groove in 
the plane II of A posteriorly by a screw d. (This on the brass in- 
strument works by a meee screw.) The semi-circular groovings 
fyf, are to fit the end of one’s fingers in moving the rotary plane I. 
The whole stands upon a firm support F,M,Q. The legs F, F, 
(of mahogany two inches square by twelve inches in elevation, i. e. 
from the top of the stand Q, to the horizontal diameter of AA,) are 
immovably secured in the mahogany stand or footing Q, which for 
the better steadying of the instrument has a leaden bottom H, one 
half of an inch in thickness by twelve inches square, attached to the 
stand Q, inferiorly, and still further to attain firmness, an iron brace 
M, one inch by one fourth of an inch, may be fastened to G, with, 
its bent end screwed in the surface of Q. 
To secure the different parts against shrinking, I would: not eit 
the given proportions (however clumsy they may appear) lessened. 
_ ‘Example.—We first place the instrument upon the table, so that 
its anterior plane receives the rays as vertically and strongly as may 
be (reflected through any uninterrupted space, for instance a window) 5 
then adjust it so that O upon the vernier and O upon the graduated 
semi-circle may stand immediately opposite to each other, i. e. 
K, p; A being in the same horizontal line. Screw the clamp G, fast. 
And with a bit of wax secure your crystal upon the projection p, 
