Accession No
6048
Brief Description
projection slides for demonstrating polarisation, by Newton and Company, English, mid-19th Century
Origin
England; London; 3 Fleet Street
Maker
Newton and Company
Class
demonstration; optical
Earliest Date
1850
Latest Date
1913
Inscription Date
Material
wood; metal (brass); glass; stone (mica); organic (unknown)
Dimensions
6048.1, 6048.3, 6048.4: length 101mm; width 52mm; depth 8mm; window diameter 47mm 6048.2: length 114mm; width 52mm; depth 12mm; window diameter 47mm
Special Collection
Provenance
Purchased from Tesseract, Box 151, Hastings-on-Hudson, New York, 10706, USA on or before 26/05/2005. Tesseract catalogue 79, Spring 2005.
Inscription
"NEWTON
3 FLEET ST
LONDON" (stamped onto each slide)
"Q.W. PLATE" (written on a label in ink on 6048.1)
"Q Wave Plate Mica" (written in ink on top edge of 6048.1)
"WEDGE" (written in ink on a label on 6048.2)
"Selenite wedge" (written in ink on top edge of 6048.2)
Description Notes
Projection slides for demonstrating polarisation by Newton & Co.; English; mid-19th century.
These four slides are used in a projection lantern fitted with a polarised light attachment to convert it into a “projection polariscope”. Three of the slides have optical material set in a round window, in a mahogany slide. The fourth slide is empty, with a spring grip for mounting one's own sample. Each slide has a mechanism for rotating the sample by turning an external brass screw. The circular window is turned by internal rack and pinion gearing.
Contents of slides:
6048.1 Quarter-wave mica preparation
6048.2 Selenite wedge
6048.3 Unknown natural sample
6048.4 Empty slide
Each slide has a removable pinion, which has each been counted as a separate part.
The quarter-wave plate converts linearly polarised light into circularly polarised light and vice versa.
When viewed through two crossed polarising filters, the selenite wedge and the natural sample will display coloured bands, which change as the sample is rotated.
References
Events
Description
These slides are used along with a projection lantern to demonstrate the strange properties certain materials have when polarised light shines on them.
Light is polarised when the vibrations of the waves are restricted to move in only one direction, in one plane. (This is actually ‘linear’ polarised light.) The lantern is fitted with polarising filters that only allow light to travel in certain directions, creating the polarised light. Filtering the light in this way reveals optical effects.
When the slides of various materials are placed between the filters, with polarised light shining on them, the materials display strange optical properties. The selenite wedge and the natural sample show coloured bands that change as the sample is rotated.
The slides would have been projected onto a screen or wall as a demonstration, but the technique of looking at these coloured bands (called ‘interference colours’) is useful for many purposes, from identifying minerals to detecting stresses in mechanical parts.
03/08/2005
Created by: Ruth Horry on 03/08/2005
FM:46517
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