class="item">A151. Negative Eye Pieces. (Huygenian), focus 5 mm. to 25 mm. Price

$4.50 A152. Diagonal Eye Piece. The prism of the eye piece has guaranteed optically plane surfaces and will not affect the definition of the telescope. Price $12.00 A153. Terrestrial Eye Piece, focus 25 mm. Price $12.00 A154. Sun Caps, to fit above eye pieces. Price $1.50

The outside diameter of all our eye pieces is 1¼" excepting those used in our Micrometers.

A201. Position Micrometers for 6" to 8" Telescopes. Circle 15 cm. diameter, divisions on solid silver, verniers reading to 6 min., slow gear motion for rotating, electrical illumination, provided with different color screens. Screw guaranteed of highest accuracy. Price	$200.00
A202. Position Micrometers for 4" to 5" Telescopes. Similar to above but rotation by hand and construction somewhat simpler. Price	$100.00

A203. Small Position Micrometer for 3" to 4" Telescopes. Circle reads to single degrees. Electric illumination. Price

$75.00

Transit Instrument, with reversing arrangement, illumination with oil or electric lamp, Filar micrometer with two eye pieces. Weight of axis balanced by springs and rollers. The circle has a diameter of 150 mm., verniers read to 20 seconds. The instrument is mounted on an iron base plate, which is fitted with azimuth adjustment (not shown in cut).

A301. Transit with 2" Telescope. Price	$550.00
A302. Transit with 3" Telescope. Price	$800.00

A401. Universal Instrument. Telescope with objective prism. Vertical circle has a diameter of 13 cm. is divided to 10 min. and reads by means of two micrometer microscopes to 10 sec. The telescope is fitted with hard phosphor bronze bearing rings and is reversible. Aperture of objective is 30 mm. Two eye pieces are furnished giving magnification of 20 and 30 diameters. The prism has absolutely plane surfaces and will not affect the definition. Striding level reads to 2 sec. The horizontal circle is protected and reads by means of two verniers to 1 min. The instrument is packed in a light but strong case. Price complete with tripod

$420.00

Note.—This instrument was first constructed for Mr. E. de K. Leffingwell, who has found it very satisfactory for his work in the polar regions.

A501. Zoellner Astrophotometer. The instrument is made to attach to the eye end of the telescope and may be used with any size of refractor or reflector. An axis parallel to the telescope tube allows the instrument to rotate as a whole. A clamp is provided to hold it in position. The artificial star is formed by a small incandescent lamp which is adjustable in any direction, and in front of which is mounted a small diaphragm. The color changing device, consisting of Nicol prism and quartz plate, is fitted with a divided circle reading to single degrees. The circle revolving with the Nicol prism for changing the intensity of the star, has a diameter of 14 cm. and reads by means of two verniers to 6 min. A concave lens is mounted in the path of the artificial star to make the light diverging at the proper angle and a plane parallel plate is adjustably fixed in the center of the box in order to throw the light in the eye piece. An achromatic objective in front of the eye piece brings the images of the real and artificial star to a focus in the same plane. Price

$150.00

A601. Small Spectroscope. Suitable for telescope from 3 to 6 in. aperture. The collimator and observing telescope have an aperture of 25 mm., focus of 200 mm. Both are fitted with rack and pinion. The spectroscope may be used with a grating or a 60 degree prism, and for this purpose has openings for the telescopes at the proper angles. A position circle of 75 mm. diameter, reading to degrees, is fitted to the instrument. The slit has micrometer head.

Price, without grating, but including 60 degree prism

$75.00

Note.—This spectroscope can also be used on a support for laboratory work.

Support for above spectroscope. Price

$4.50

A602. Spectroscope for telescopes from 6 in. to 18 in. aperture and detailed description on application.

A701. Chronograph for physical and astronomical work. This chronograph is designed to meet the demand for a medium sized, well-made and accurate instrument of this kind and has given very good satisfaction. The cylinder is 15 cm. in diameter 25 cm. long, driven by strong, carefully made clock work, fitted with friction governor. Two different speeds for the cylinder can be obtained by means of change gears. The slow speed of the drum is one revolution per minute, and at this speed the drum will run for a full hour. The fast speed is 30 seconds per revolution. The carriage is driven by means of a screw, the nut of which is made to disengage