Optical projection: a treatise on the use of the lantern in exhibition and scientific demonstration (1906)

Page scan 000364 from Optical projection: a treatise on the use of the lantern in exhibition and scientific demonstration

Record Details:

Title:
Optical projection: a treatise on the use of the lantern in exhibition and scientific demonstration
Date:
1906
Author:
Wright, Lewis, 1838-1905
Publisher:
London, New York, Bombay : Longmans, Green and Co.
Volume:
Optical projection: a treatise on the use of the lantern in exhibition and scientific demonstration
Leaf #:
000364
Language:
English
Collection:
Books
Format:
Books
Contributor:
University of California Libraries
Sponsor:
MSN
Coordinator:
Media History Digital Library
Description:
Date Added:
July 19, 2022
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POLARISED LIGHT 349 CHAPTER XXH POLARISED LIGHT 198. Double Refraction.—This can be demonstrated in a simple rhomb of calcite, by employing the ' focussed parallel beam' (p. 277) from a pin-hole aperture on the flange- nozzle. The spar ought not to be less than four inches long if the separation is to be easily visible, though its other dimensions may be quite small, such as half an inch in the side. A wider separation is shown by placing an aperture in the stage of the optical front, and a double-image prism on the nozzle, focussing the aperture as small discs upon the screen. 199. Huygens' Experiment.—For this a pair of double- image prisms are mounted somewhat as in fig. 196, N fitting into the nozzle of the optical front, in front of the power. The first prism A is mounted in this tube, the second prism B in a cell which can be rotated easily. The two prisms must be chosen to match, and a slot or stage s should be provided between them. Focus- sing the aperture, the alternate dis- appearance and augmentation of the images will be seen on rotating the front prism. The slit 8 is for the insertion of a film of selenite between the two prisms, which will give tl»:e beautiful phenomena of comple- mentary colours. Inserting rather a larger aperture in the stage, so that the pair of discs somewhat overlap, it will be shown that the two overlapping colours always produce white. It is well to have a small slide in which are mounted two such selenites, one giving a green and red, and the other blue &nd yellow. FlG. 196.—Huygens' Apparatus