CHAPTER XII.

INSTRUMENTS TO MEASURE SUBTENSE OR TANGENTIAL ANGLES TO ASCERTAIN

DISTANCES:--Historical Notes of the Method--Principles Involved--

Stadia Measurements, Direct and by the Ordinary Telescope--

Corrections for Refraction of the Object Glass--Stanley's Subtense

Diaphragm--Anallatic Telescope of Porro--Tacheometers--Stadia--

Omnimeter--Field book--Bakewell's Subtense Arrangement 355