Instrument for the determination of the optic axial angle
(2V). The instrument was used to measure the apparent
angle made by the optic axes of a biaxial crystal in air
(2E) or in oil (2H). The true angle between the optic
axes (2V) may be obtained by correcting the measurement
for the refractive index (β) of the crystal. The measurement
is done on a crystal section cut at right angles to the
Lacquered brass, nickel plated brass and oxidized brass.
Graduated circle diameter: 16 cm, height: 32 cm, total
length: 33 cm. Signed: "R. Fuess Berlin". First
half 20th century.
for the History of Sciences, Universiteit Gent, Belgium
(inventory number: MW 01/4932)