filar micrometer
Date: circa 1900
Inventory Number: 1996-1-0032
Classification: Micrometer
Subject:
Maker: English ?
Owner: Carl Bosch (1874 - 1940)
Owner: Donald H. Menzel (1901 - 1976)
User: Harvard College Observatory (founded 1839)
Donor: Department of Astronomy, Harvard University (founded 1839)
Associate Name: James G. Baker (1914 - 2005)
Cultural Region:
City of Use:
Dimensions:
micrometer: 12.2 × 38.6 × 37.2 cm (4 13/16 × 15 3/16 × 14 5/8 in.)
box: 18.6 × 43.6 × 41.2 cm (7 5/16 × 17 3/16 × 16 1/4 in.)
Accessories: 6 eyepieces; case
DescriptionThis large, elaborate micrometer is designed to screw onto a telescope with an aperture of 5 1/4 inches. It has two curved, chrome-plated handles for steering the tube.
The micrometer is made of brass with silvered scales. The rotational scale is divided 0- 360° every 15 minutes and has 2 verniers reading to 1 minute of arc. Lamps and reading microscopes are at each vernier. Two clamps with a slow motion screw are on the scale.
A steel screw with a knurled hard rubber or plastic knob at each end moves the lower part of the micrometer longitudinally in a track. Two smaller screws move the eyepiece longitudinally in separate tracks at right angles. The micrometer drum has three scales. Each is divided into 100 units. A dial is divided into 60 parts with a pointer.
The instrument has lamps to illuminate cross hairs. There is a rheostat and switch to vary the power.
There are six eyepieces. The fitted box is padded with green felt. The top plank of the lid is separated from the rest of the box.
The micrometer is made of brass with silvered scales. The rotational scale is divided 0- 360° every 15 minutes and has 2 verniers reading to 1 minute of arc. Lamps and reading microscopes are at each vernier. Two clamps with a slow motion screw are on the scale.
A steel screw with a knurled hard rubber or plastic knob at each end moves the lower part of the micrometer longitudinally in a track. Two smaller screws move the eyepiece longitudinally in separate tracks at right angles. The micrometer drum has three scales. Each is divided into 100 units. A dial is divided into 60 parts with a pointer.
The instrument has lamps to illuminate cross hairs. There is a rheostat and switch to vary the power.
There are six eyepieces. The fitted box is padded with green felt. The top plank of the lid is separated from the rest of the box.
Signedunsigned
FunctionA filar micrometer of this sort is a precision eyepiece for a telescope in which small separations between objects can be measured. One typical astronomical use would be in observing the separation of double stars.
Historical AttributesUsed at Harvard College Observatory and by Donald Menzel, a specialist on the sun and director of the Observatory from 1952 until 1966.
Either Menzel or the Observatory received the micrometer as a gift of Carl Bosch circa 1920. James G. Baker appraised it for the Observatory when it was given to CHSI in 1973.
Either Menzel or the Observatory received the micrometer as a gift of Carl Bosch circa 1920. James G. Baker appraised it for the Observatory when it was given to CHSI in 1973.
Curatorial RemarksThe file and tag state that the micrometer was presented to Dr. Menzel by Carl Bosch, circa 1920. However, Dr. Menzel would have been a college student of 19. It is more likely that this was given to the Observatory around 1920 or to Menzel much later in his career.
There is correspondence between Dr. Menzel and DPW in instrument file.
There is correspondence between Dr. Menzel and DPW in instrument file.