contour finder, or stereo slope comparator
Date: circa 1950
Inventory Number: 1996-1-0528
Classification: Contour Finder
Subject:
Maker: Abrams Instrument Corporation (ca. 1930-present)
Cultural Region:
Place of Origin:
Dimensions:
9.8 × 23.5 × 13 cm (3 7/8 × 9 1/4 × 5 1/8 in.)
Description:
This instrument is made of a black-crackle finish frame, and is essentially a stereoscope. It has two circular stereoscopic lenses which can pivot and slide, but not rotate up and down. This motion is to accomodate the eyes of different users.
The parallax measuring unit is composed of a cylindrical supporting rod on which are coiled springs. Two rectangular glass plates are mounted at right angle to this rod, which moves the plates horizontally with the help of a micrometer screw. A micrometer gauge displays in units of 0.01 millimiter the distance moved. A similar gauge measures the vertical displacement of the glass plate on the right. The plates have small etched indicator dots.
The parallax measuring unit is composed of a cylindrical supporting rod on which are coiled springs. Two rectangular glass plates are mounted at right angle to this rod, which moves the plates horizontally with the help of a micrometer screw. A micrometer gauge displays in units of 0.01 millimiter the distance moved. A similar gauge measures the vertical displacement of the glass plate on the right. The plates have small etched indicator dots.
Signedon both dials: ABRAMS
FunctionFor measuring the strikes and dips (or the topography) of geologic formations in aerial photographs.
This is how the introduction to the 1945 patent describes this instrument: "In aerial mapping it is customary to take a series of photographs, either vertical or oblique, at definite intervals while the airplane carrying the camera flies on a definite course at a definite elevation. The photographs are taken often enough so that there is a relatively wide overlap of adjacent photographs. It is possible to accurately determine the relative elevations of a number of points on the earth's surface by measuring the parallax of those points in two such overlapping vertical aerial photographs, or two oblique aerial photographs rectified to the vertical, taken in the above manner. Essentially the present invention is a device for accurately measuring the parallax in such photographs and thereby determining elevations of points on the ground, although the invention has a number of other uses such as, for example, interpretation of microscopic and X-ray photographs."
This is how the introduction to the 1945 patent describes this instrument: "In aerial mapping it is customary to take a series of photographs, either vertical or oblique, at definite intervals while the airplane carrying the camera flies on a definite course at a definite elevation. The photographs are taken often enough so that there is a relatively wide overlap of adjacent photographs. It is possible to accurately determine the relative elevations of a number of points on the earth's surface by measuring the parallax of those points in two such overlapping vertical aerial photographs, or two oblique aerial photographs rectified to the vertical, taken in the above manner. Essentially the present invention is a device for accurately measuring the parallax in such photographs and thereby determining elevations of points on the ground, although the invention has a number of other uses such as, for example, interpretation of microscopic and X-ray photographs."
Curatorial RemarksAll the information on this instrument is found in the patent granted on 25 February 1945, patent number 2,369,634. It can be read online here.