A1204. Comparator. For Plates 8×10 inches. This machine was constructed
in accordance with suggestions given by Dr. Frank Schlesinger, Director of
Allegheny Observatory. The ways are carefully straightened to within 0.002
millimeter. The carriage is moved by two racks and pinions and has a large
handle on each side. Two concentric circles are fitted to the carriage, the
inner circle carries the plate with the film in a fixed plane, no matter
what the thickness of the glass may be. Both circles are provided with
clamps and tangent screws, so that each one may be clamped and adjusted
independently. The outside circle carries four index points 90 degrees
apart. One of these marks is made adjustable. These four marks serve to
turn the plate exactly 90 degrees so as to measure rectangular
coordinates. The guide carrying the measuring microscope is adjusted
exactly at right angles to the ways of the bed plate. The carriage
supporting the microscope is moved by rack and pinion. The microscope is
arranged to tilt, so as to view either the plate or the scale above. The
eye piece is provided with a reversing prism. Measurements are made on the
scale divided in millimeters. The smaller measurements, to 1-4000 of a mm.,
are made by the micrometer. The micrometer is fitted with sliding eye piece
and counter for full revolutions. The scale is not marked in the usual way
with single lines, but each millimeter is marked with a double line. This
double line allows the use of one single spider thread, which is preferable
to use for bisecting the star, and the double line on the scale allows a
clear setting with the single spider thread. The stage is fitted with an
adaptor for holding plates 4×5 inches. Price
$450.00
This machine has been in use during the last years at the Yerkes Observatory and has been found very convenient and satisfactory in every way.
A graduated circle can be provided if desirable. Such division on solid silver, with verniers reading to 1-100 of a degree will increase the cost $50.00.
A1205. Comparator, for plates 4×5 in. of the same design as A1204.
Price
$300.00
A 1206
A1206. Comparator. A larger machine of the same design as A1204 with scale of 45 cm. length, divided in double lines to 0.25 mm., and with two carriages, one for spectrum plates of 18 in. length and the other with divided circles for star photographs 12"×14". This instrument was constructed for the Solar Observatory of the Carnegie Institution at Mount Wilson, California.
