tribrach

In a recent examination of the registers of the Ryde Philosophical Society, Mr. Martin has found, as I have been informed through Mr. Westropp’s kindness, the entry, that the flint tribrach was presented to the collection by the late Dr. Martin in 1853, with other objects from Ventnor, and as having been obtained on the shore at that place.

An optical plummet, built into either the tribrach or alidade of total station instruments, permits accurate centering over a point.