SLES, 
FATTTH & CO., WASHINGTON, D. C 25 
ALTITUDE AND AZIMUTH INSTRUMENTS. 
Cut No. 43 represents one of our larger instruments, which was on 
exhibition in the International Exhibition at Philadelphia, for which 
we received an award. 
It is of superior construction, and differs from other instruments of 
this class in many important particulars. Not being a “ repeating 
instrument,” strictly speaking, and, therefore, not liable to the defects 
inherent to repeaters, yet both the horizontal and vertical circles can 
be shifted for position, so as to bring a different part of the graduation 
under the microscopes. The circles are divided on silver into five 
minute spaces, reading by micrometer microscopes to single seconds. 
The standards radiate out from the centre, and are high enough to let 
the telescope swing through. The pivots of the telescope axis rest on 
agate, and are made of phosphor-bronze; a delicate striding level* 
reading to seconds, to go over pivots, is provided; pivots are pierced 
to allow the field to be illuminated; the horizontally of the micro¬ 
scopes for vertical circle is controlled by a chambered level, reading to 
seconds. The illumination of the graduation is effected by means of 
prisms receiving light from above and throwing it out radially, thus 
insuring the same condition of light in any position of the microscopes. 
Both circles are entirely free of clamps and tangent-screws, these 
being attached to a collar, so as not to produce any strain on the circle. 
No. 43.—Altitude-Azimuth, as described above ; horizon¬ 
tal circle eighteen, vertical circle twelve inches in 
diameter; former reading by three, and latter by two 
microscopes. Telescope 3-inch clear aperture, 28 inches 
focal length, with micrometric eye-piece. Levels are cham¬ 
bered, and read to seconds ; packed complete in two boxes, 
with positive and diagonal eye-piece, two lamps, and all 
accessories....... .... $2000.00 
No. 44.—Same, without vertical circle, and standards only 
high enough for observation of Polaris......’. 1200.00 
No. 45.—Same as No. 43, and exactly like cut; horizontal 
circle twelve, vertical circle ten inches in diameter; 
, former reading by three, latter by two microscopes. Tele¬ 
scope 2|-inch clear aperture, 24-inch focus, packed complete. 1300.00 
No. 46.—Same, without vertical circle, standards as in No. 
44, telescope 2-inch aperture, packed complete... 800.00 
No. 47.—Same as No. 46, circle reading by two instead of 
three microscopes, in other respects similar to No. 46.. 600.00 
No. 48.—Same as No. 43, and shown on cut; horizontal cir¬ 
cle ten, vertical circle seven inches in diameter ; former 
reading by three microscopes to seconds, the latter, by 
means of level alidade, to ten seconds. Telescope swing- 
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