ft side of the instrument so as to have the right hand free for recording
readings.

A set of change gears can easily be engaged to give a fast motion to the
carriage. The stage will hold plates from 3 to 8 cm. in width and of 60 cm.
in length. It can be shifted lengthwise for a distance of 25 cm. and is
provided with adjustment for aligning the plates. The whole stage can be
easily removed from the instrument.

The microscope is fitted with variable magnifying power and is of standard
size. Price #$450.00#

#Note.#--The design of this comparator was suggested by Prof. Humphries,
Director Laboratory of the U. S. Weather Bureau, for whom the first one was
built.

[Illustration: A 1203]

#A1203. Comparator for Star Photographs#, measures in one direction 80 mm.
and under right angle 60 mm. The lower part is constructed similar to our
Comparator A1201. The top slide carries a divided circle for measuring
position angles. The circle is arranged similar to a position micrometer.
It is fitted with quick gear motion and tangent screw and the two verniers
read to 1-100 degree. The microscope has variable magnifying power and is
provided with reversing eye piece. This machine has been furnished for and
is in use at Yerkes, Lick and Kirkwood Observatories. Price #$365.00#

[Illustration: A 1204]

#A1204. Comparator.# For Plates 8x10 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