You searched for:
“heliometry”
The use of a telescope with a movable split-lens objective, primarily to measure the angular distance between two stars; originally used to measure the diameter of the sun.
This entry is located in the following units:
helio-, heli-
(page 3)
meter-, metro-, metr-, -metrical, -metrically, -metron, -metric, -metrist, -meter, -meters, -metry, -metre
(page 17)