Description:
- Object ID: ALSA 2012.02.02
- Made by: Keuffel & Esser Co.
- Model: Unknown.
- Serial Number: 103971
- Date Made: Unknown.
- Approximate size: 29 cm X8.5 cm X 0.2 cm thick
- Accessories: wooden case.
- Condition: good
Commentary:
The alidade has stadia lines (two short horizontal lines, one above and one below the horizontal crosshair). The distance from the instrument to a stadia rod is determined by subtracting the bottom stadia reading from the top reading and multiplying the difference by a constant, usually 100. It also had a vertical circle so that the slope of the measurement could be determined for reducing slope distances to the horizontal and also to determine the difference in elevation.
Alidade, Keuffel & Esser Co., Serial No. 103971 matching tripod and plane table ALSA 2012.02.02. The instrument is brass and consists of a telescope mounted on a flat plate (29 cm X8.5 cm X 0.2 cm thick). Attached to the plate is a trough compass (12.5 cm X 2 cm X 2 cm height), a circular bubble (2.5 cm diameter X 1.2 cm high), two chromed thumb knobs for orienting the plate, two graduated scales (one on either side of plate) and markings “KEUFFEL & ESSER CO.” and Serial No. “103971” engraved in the top of the plate. The scope (25 cm long X 4 cm diameter) is mounted on a round pedestal attached to the plate. A striding level is attached to vernier connected to the scope.
The wooden box is comprised of two pieces. The small top section is attached to the bottom section by one 10 cm brass hinge at the back and a brass clasp on the front. It is 32.5 cm (h) X 12 cm (w) X 12.5 cm (l) and the four bottom corners are reinforced with four brass metal corner pieces. On the bottom of each brass metal corner is a round rubber foot. The inside of the box is slotted near one side to hold the instrument in place. There is a label inside the top of the case describing the Model and Serial numbers and other pertinent information describing the instrument, the name of the company and the addresses. The case has an elongated leather strap (approximately 2 meters long) that is held in place by two straps on either side of the box.
Source of Object: Donated by Lou Breton, ALS (Hon. Life).
Notes: The Society has only one in their collection.
References: Visit article The Survey Instrument Captain Cook Wanted to Learn – The Plane Table and Alidade for additional information.
Description by: Entered by Ed Titanich on December 23, 2024.