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

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 #:
00033
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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18 OPTICAL PROJECTION abandoned now, because the aberrations are very imperfectly corrected, and there is loss oi light by reflection at the edges, the curve increasing the angle of incidence. The two meniscus lenses of D were better, but never came into general use, being superseded by F, a meniscus and double convex, with the meniscus towards the radiant. This is known as the Herschel condenser, being in general form modelled on a burning-glass designed by Sir John Herschel, and was long reputed to be free from spherical aberration, though it was afterwards discovered that this supposition was due to an error in calculation. As a burning-glass, however, such a pair does give exceedingly good results ; and, correspondingly, is excellently adapted for converting the light from a luminous Fro. 10 point into a parallel beam. The light from a lantern has however to be converged, except in optical experiments; and therefore this condenser is not so superior for lantern use; but it does well for lanterns used with the lime-light alone, and is largely employed for such ; for larger radiants, like lamps, it is not well adapted. Its best form is that devised by Gravett, shown at a, where the meniscus next the light is made rather smaller, and the second lens is of flatter curve on the inner face. Optically, this is a very good condenser for the lime-light, its principal defect being that the bulging front prevents slides being brought up close to the margin, and hence somewhat diminishes the size which can be illumi- nated by a condenser of given diameter.