ZEISS SCREW COVER-GLASS MICROMETER

DESCRIPTION

HISTORY

DESCRIPTION:
This is a screw micrometer integrated into a black painted heavy iron base. The base measures about 80 mm in diameter and it is about 80 mm from the bottom of the base to the top of the widest part of the drum. It is signed on the inset tab(left): CARL ZEISS, JENA in the lens insignia of Zeiss, and under that it says ¹/₁₀₀, 0-10mm. This refers to the division, on the drum and the total capacity of the device. On the front of the base a decal of silver color reads in a small box Germany. The drum is calibrated in 0.01 increments from 0 to 100. The arrow on the stem under it registers single mm as the drum is unscrewed. The drum is cross-hatch knurled as is the smaller knob on the end; this smaller knob(right), has a ratcheting mechanism to prevent overtightening which could not only break the glass, but lead to an inaccurate reading.
 

HISTORY:
Zeiss sold two basic types of coverglass (coverslip) micrometer. These include the screw micrometer type, (simpler and less expensive, as shown on this page) and the dial micrometer, shown on another page. The screw micrometer was made in 3 forms over the years. Early on, the first form of 'Cover-Glass Tester' that I am aware of contained a 'screw with divided disc and arrangement to regulate the zero-point'. The screw with disc form was offered but not pictured in the Zeiss catalogs of 1889 and 1891, but I am unaware of when it was first offered. In 1906 the micrometer with 'divided drum,' the second form, as shown on this page, was offered and continued to be sold through at least 1927. The third form, of a slightly different shape, and slight shorter than the second form, then continued through 1942. I have never seen an illustration of the early 'disc' form. The Zeiss dial micrometer was sold from at least 1885* through 1913, but the screw micrometer shown on this page which was first offered sometime after 1913, continued to be sold through 1942. Another less stout form of coverslip micrometer with a base was sold in the early 20th century by Seibert. And there was a Leitz version as well. A freestanding lacquered brass screw coverglass micrometer is also on this site.

*Thanks to Dr Joe Zeligs for the data from the 1885 catalog