Signedprinted on paper: HARVARD COLLEGE OBSERVATORY
in pencil on each slide: Ladd
InscribedBoth slides are marked in pencil: B. 17. Airys Spirals
FunctionQuartz has a crystal structure that spirals either to the left or to the right along the direction of the optic axis. If viewed with a conoscope (a strain free acrylic or glass sphere on a rod), one sees a "bull's-eye." With the addition of a quarter wave plate, the bull's-eye becomes two spirals, which spiral either to the left or right, showing their left-handedness or right-handedness. These spirals are named Airy Spirals after Sir George Biddell Airy who first described the phenomenon in 1831.
ProvenanceHarvard College Optics Lab; transferred to CHSI, 10/19/1967