Accession No

2007

Brief Description

Powell’s wave apparatus, model of optical wave motion, by Elliott Brothers, English, 1875 (c)

Origin

England; London; 449 Strand

Maker

Elliott Brothers [maker] Powell, Baden [designer]

Class

physics; demonstration

Earliest Date

1864

Latest Date

1886

Inscription Date

Material

wood (mahogany and one other); metal (brass, steel); plastic (ivorine)

Dimensions

length 320mm; breadth 175mm; height 920mm

Special Collection

Cavendish collection

Provenance

Transferred from Cavendish Laboratory, University of Cambridge, 1974.

Inscription

‘ELLIOTT BRORS.
449 STRAND
LONDON’ (ivorine plaque on base)

Description Notes

‘Powell’s wave apparatus’, model of optical wave motion, by Elliott Brothers, English, c. 1875.

Rectangular mahogany base with four feet supports two mahogany standards. A horizontal mahogany bar is set between the two standards and can be adjusted for height by knurled brass screws on other side. Passing through the bar are 24 steel rods topped by white-painted wooden balls. The lower end of each rod is attached to a brass ring, which is fixed eccentrically to a brass bar set between the two standards. This brass bar is rotated by a brass crank handle, so causing the rings to turn and the white balls to demonstrate the motion of a wave.

Complete

References

Chris Haley; 'Wave machines'; Explore Whipple Collections online article; Whipple Museum of the History of Science; University of Cambridge; 2015: https://www.whipplemuseum.cam.ac.uk/explore-whipple-collections/models/wave-machines

Events

Description
Baden Powell (1796-1860) was Savillian Professor of Geometry at the University of Oxford from 1827. Much of his research concerned radiant heat, and its possible relation to visible light. Powell originally designed this wave machine in the 1830s, but this example was manufactured by Elliott Brothers of London around 1875. Its provenance suggests that this model was purchased for use in teaching demonstrations in the Cavendish Laboratory of the University of Cambridge.

The model is designed to illustrate how unpolarised or circularly polarised light can be polarised by confining the wave motion to one plane. When the handle is turned, the circular rings at the bottom rotate about the handle’s axis, representing the helical propagation of unpolarised light. By attaching bars to these rings that are only able to move in a single plane, the ivory balls at the top of the bars (which nominally represent ‘ether particles’) illustrate polarised optical wave motion, which takes the form of a familiar sine wave. By moving the horizontal bar near the top of the model, the particles may also be allowed to oscilate along a second axis perpendicular to the first, so that the wave displays circularly polarised light.

Powell’s design was based on that of a model constructed by George Biddell Airy, though unfortunately no details of Airy’s machine appear to have survived. Powell remarked that “a glance” at a model like his own “enables the mind to grasp the idea at once, even when unaccustomed to the mathematical analysis of it.”
28/05/2014
Created by: Joshua Nall [using material written by Christopher Haley] on 28/05/2014

FM:45497