Chapter 2

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.

#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#

#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 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 4x5 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 4x5 in. of the same design as A1204. Price #$300.00#

#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"x14". This instrument was constructed for the Solar Observatory of the Carnegie Institution at Mount Wilson, California.

_NOVEMBER, 1905_

Wm. Gaertner & Co.

Astronomical, physical and physiological Apparatus

5347-5349 LAKE AVENUE CHICAGO

Spectrometers and Accessories

#Cat. No. L4020 LABORATORY SPECTROMETER.# This instrument is very rigid and accurate in construction and every part of its design has been carefully considered. The circle has a diameter of 15 cm. and the two verniers read to 20 sec. It is fitted with protecting plate which adds greatly to the value of the instrument if put in the hands of students. The graduation is on solid silver. The verniers are fitted with adjustable magnifying glasses, the telescopes have an aperture of 25 mm., focal length of 200 mm. A horizontal adjustment for the telescope is provided. No provision is made for radial adjustment, which correction is made before the instrument is sent out. The slit is accurately constructed; the jaws are of German silver and it is provided with comparison prism. The eye end of the observing telescope is of standard size so as to receive our micrometers M201 or M202, or the Auto Collimating eye piece (Lamont & Abbe) M540. Gauze eye piece is fitted to the instrument. The prism table and observing telescope have independent movements and each is provided with clamp and tangent screw. The prism table can be clamped to any part of the vernier plate. The prism holder has convenient leveling arrangement and will hold prism up to 35 mm. in height. The instrument is arranged to receive Fuess centering apparatus and crystal holder. A 60 degree heavy flint glass prism of best optical quality is included.

Price $75.00

#L4020b CAMERA ATTACHMENT# will fit in place of the observing telescope. It is fitted with long focus objective and standard plate holder 2 1/2"x 2 1/2". The plate holder is provided with swivel for proper focusing of the spectrum. The slit is so arranged that four exposures can be made on one plate.

Price $20.00

#Cat. No. L4020c SCALE TUBE.# The third arm of the instrument can be easily attached and rotated and clamped in any position. It may also be used for holding a second Collimator.

Price $20.00

#Cat. No. L4021 STUDENT'S SPECTROMETER.# This instrument is in every respect similar to our L4020, but some of the higher finish has been omitted. All the essentials are carefully constructed and the optical parts are of the best quality. The circle is protected but only one vernier reading to 30 sec. is fitted to the instrument. The magnifying glass is omitted.

Price, including prism $60.00

TRANSCRIBERS' NOTES

General: Corrections to punctuation have not been individually noted.

General: Inconsistent spelling of catalog/catalogue preserved as in original.

Page 7: magnifiing corrected to magnifying and celestrial corrected to celestial.

Page 17: intensisy corrected to intensity.

Page 18: hundreths corrected to hundredths. LaPlatta as in original.

NB The final two pages of the book, on Astronomical, physical and physiological Apparatus, are in a slightly different format in the original. Particularly, prices are not in bold. That has been preserved in this version.