Explorer's Alidade
Detailed Description
Manufactured by Keuffel & Esser, New York & New Jersey. In this type of alidade, as opposed to the high standard, the telescope mounted close to the straightedge, producing a more compact instrument. A right-angle prism is attached to the eyepiece and permits viewing by looking down. A cylindrical bubble and magnetic compass needle are attached to the base; these are used to level and orient the plane table to its proper position.
Object ID: USGS-000161
Sources/Usage
Public Domain.