filar micrometer
Date: circa 1900
Inventory Number: 1996-1-0032
Classification: Micrometer
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.