Sonometer
Aiton's Encyclopedia (1910)
an instrument for determining the laws of sounding strings. It consists usually of two or more piano wires of known weight, stretched over a sounding box, with devices, usually weights, for increasing their tension. The laws of sounding strings are very interesting: 1. The heavier the string, the lower the tone. For strings of the same length and tension, the pitch varies inversely as the square root of the weight. If one string be four times as heavy as another, its pitch will be half as high, that is to say, an octave lower. If a third string be added whose diameter is three times that of the first, and whose weight is consequently nine times as great, it will vibrate one third as many times per second as the first string. 2. If two strings have the same length and size, but carrying unequal weights, the tighter string will give the higher note. For strings of the same length and size, the pitch varies directly as the square root of the tension or stretching weight. If two strings otherwise alike be stretched with weights of one and four, the note of the second will be an octave higher than that of the first. If a third and similar string be added, sustaining a streching weight of nine, it will vibrate three times as frequently as the first string. 3. The shorter the string, the higher the note. If two similar strings be stretched to the same tension, and with lengths of one and two respectively, the note of the first will be an octave higher than that of the second. If a third string be added whose length is three times that of the first, the first will vibrate three times as often as the third. If a sounding string be held motionless at its middle, its half produces a note an octave above that produced by the whole string. By using strings of different weight, and by varying the length of the sounding segment with his fingers, the violin player is able to produce an apparently limitless variety of notes. Tuning a piano consists in giving each wire its proper tension, so that it will vibrate with desired frequency and produce the tone expected from it. See Violin ; Piano ; Sound
What Has Changed in the Last Century
The three laws Aiton's set out in 1910 — pitch varying inversely with the square root of the string's mass, directly with the square root of tension, and inversely with length — are the same laws taught today; they were already old when the entry was written, having been stated by Mersenne in 1636. The sonometer itself survives almost unaltered as a school and undergraduate physics apparatus, still a wire over a hollow box with hanging weights and a movable bridge, though the frequency is now usually read from an electronic counter, oscilloscope or phone app rather than matched by ear against a tuning fork. The one practical trade Aiton's mentions has moved on: piano tuners still set each wire's tension, but most now work with an electronic tuning device alongside the ear. The word sonometer has also drifted, and in medical and audiological use it more often denotes an instrument for measuring sound levels or hearing.
Written for this edition, 2026.