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274 Al'PENUlX.
country, and establish fresh claims to the gratitude of your countrj
men, is the sincere ms h of.
Sir,
Your obliged and faithful servants.
F o r DICKSON, PBICE, and C o .—W. HODGSON.
NATICH, KENDAII, and Co.
F o r LAYLEM, READ, and Co. —VALENTINE
SMITH.
SWAYN, REID, and Co.
LANG, PEAKCE, and Co.
FREDK. HUTH, GRUNING, a n d Co.
F o r GIBBS, CRAWLEY, and C o . — H . WITT.
J . W . LEADLEY.
F o r HEGAN, HALL, and CO.—J . FARMER.
J O H N MACKIE.
J . SUTHERL.AND.
F o r CHRISTOPHER BRIGGS. — H . N . BRIGGS.
TEMPLEMAN and BERGMAN.
FREDERICK PFEIFFER.
NO. 44.
DESCRIPTION of a QUADRANT, the power of which is increased by
means of an additional Horizon Glass.
Let C A B, in the figure, represent a common quadrant, having
the angle A C B equal to forty-five degrees : let C be the index-glass ;
C A the zero line, or the plane of the glass produced; D the horizon
glass, and E the sight-vane.
Suppose C and D to be parallel, and that a ray coming from an
object H, is reflected from C, along the line C D, and from D along
the line D E to the eye.
A ray of Ught from h may be supposed to come from H, if the
two, H h, are more than half a mile from the uistrument, and the
object H -nTll be seen directly, as well as by reflection, in the line D E.
The angle D C E being equal to the angle DEC, D C is equal
to D E. With the centre D describe the cnrcle C E F. Place a
glass at F, similar to that at D, but making an angle with C B,
which will reflect a ray passing along C F, in the line F E, to E.
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