Description:
- Object ID: ALSA 2010.06.07
- Made by: Bausch & Lomb Optical Co. Rochester N.Y. U.S.A.
- Model: Unknown.
- Serial Number: Unknown.
- Date Made: Prior to 1930.
- Approximate size: Brass plate: 31 cm X 7 cm. The telescope is 21 cm X 3.5 cm diameter. Alidade is 19 cm high
- Accessories: Wooden box: 33 cm X 21 cm X 11 cm, trough compass, screwdriver, a brass two pinned attachment and a thumb screw presumably for attaching the trough compass.
- Condition: Fair
Commentary:
The alidade is used for plane table mapping. Objects are sighted on through the telescope. and the direction of them are marked on the map sheet using the edge of the bottom plate. Because this alidade has a telescope with cross hairs it can be used to determine distances using stadia and because it has a vertical circle vertical angles can be measured so slope distances can be reduced to the horizontal.
“BAUSCH & LOMB OPTICAL CO. ROCHESTER N.Y. U.S.A” is engraved in the top of the brass plate of the alidade. As well “GSC 89” is hand etched on one end of the plate. GSC likely standing for Geological Survey Canada.
The number “9840” is engraved on the side of the trough compass as well as “BAUSCH & LOMB OPTICAL CO. ROCHESTER N.Y. U.S.A”.
On the inside of the wooden box are two lables. One showing a repair done on April 15-30 and an adjustment made on 12-5-30. The other, a Bausch and Lomb lable showing instrument specifications.
The accession for this objects also included a plane table (ALSA 2010.06.03), a plane table tripod (ALSA 2010.06.02) and an open-sight alidade (ALSA 2010.06.04).
Source of Object: Donated by Steve Cherwonick, ALS#238.
Notes: The Society has two others 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. Gordon Olsson on February 1, 2026.