Sound / by John Tyndall.

  • Tyndall, John, 1820-1893.
Date:
1883
Catalogue details

Licence: Public Domain Mark

Credit: Sound / by John Tyndall. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    452/494 (page 428)
    To these illustrations of rectangular vibrations I add two others, figs. 196 and 197, from a very beautiful series obtained by Mr. Hubert Airy with a compound pendulum. The experiments are described in ' Nature' for August 17 and September 7, 1871. As their loops indicate, the figures are those of an octave, and a twelfth.. But the most instructive apparatus for the compound- ing of rectangular vibrations, is that of Mr. Tisley. Figs. 198 and 199 are copies of figures obtained by him through the joint action of two distinct pendulums ; the rates of vibration corresponding to these particular figures being 2 : 3 and 3 : 4 respectively. The pen which traces the figures is moved simultaneously by two rods attached to the pendulums above their places of suspension. These two rods lie in the two planes of vibration, being at right angles to the pendulums, and to each other. At their place of intersection is the pen. By means of a ball and socket, of a special kind, the rods are enabled to move with a minimum of friction in all directions, while the rates of vibration are altered, in a moment, by the shift- ing of movable weights. The figures are drawn either with ink on paper, or, when projection on a screen is desired, by a sharp point on smoked glass. When the pendulums, having gone through the entire figure, return to their starting-point, they have lost a little in ampli- tude. The second excursion will, therefore, be smaller than the first, and the third smaller than the second. Hence the series of fine lines, enclosing gradually diminishing areas, shown in these exquisite figures.1 Mr. Tisley's apparatus reflects the highest credit upon its able constructor. Sir Charles Wheatstone devised, many years ago, a small and very efficient apparatus for the compounding 1 For some beautiful figures of this description I am indebted to Pro- fessor Lynam of Yale College.