Gurley Aero-1930-USN-No. 49-41
The Gurley Aero-1930-USN theodolite is a friction driven vernier balloon theodolite. Built by Gurley instruments in 1942 these instruments meet a navy specification for pilot balloon theodolites. They are more basic than the ML-47 specification David White 6061 theodolites beginning there service with the Army Signal Corps at that time.
The Gurley balloon theodolite has gun sites and a fixed focus objective. The eyepiece has a focus for the cross hairs but the objective is fixed focus. The telescope does not have a switchable wide angle objective. Azimuth is viewable from the back side of the instrument but elevation is not. The Gurley was available with an option of lighting for the scales and reticule.
The photo below c. 1944 shows the the theodolite in action with two Navy Wave Aerographer's Mates, an official US Navy photograph from the National Archive.
 |
 |
 |
In the photo left you can see the friction
driven elevation control knob, a separate azimuth friction control knob i
under the rear of the theodolite The instrument is read with two 10 part vernier scales
yielding 6 minute accuracy. The azimuth and elevation scales are directly above each other for
quick reading.
|