Music and Mechanics

Flies, wheels and trapezoid violins

Our story begins with a chance encounter on a street in London, in August 1666 - just a month before the Great Fire of London. Here’s how the 17th century diarist, Samuel Pepys, describes his meeting with the scientist, Robert Hooke.

Up, and with Reeves walk as far as the Temple, doing some business in my way at my bookseller’s and elsewhere, and there parted, and I took coach, having first discoursed with Mr. Hooke a little, whom we met in the streete, about the nature of sounds, and he did make me understand the nature of musicall sounds made by strings, mighty prettily; and told me that having come to a certain number of vibrations proper to make any tone, he is able to tell how many strokes a fly makes with her wings (those flies that hum in their flying) by the note that it answers to in musique during their flying.

Samuel Pepys

Robert Hooke (1635-1703) began his career assisting the scientist Robert Boyle in his experiments on the relationship between gas, temperature and pressure. Hooke constructed the vacuum pump for Boyle; and, later, he built telescopes and microscopes. Hooke used the microscope to explore the structure of flies and other tiny species.

Hooke also made engravings of the fly, seen here in his publication, Micrographia (1665).  And, in his conversation about sound with Samuel Pepys, Robert Hooke uses the beating of the fly’s wings as a way of explaining sound frequency.

Hooke designed and built a wheel with regular teeth marks around its edge. As the wheel span, the teeth struck a card, making a noise. The faster the speed of the wheel, the higher the frequency of the teeth hitting the card.

Every time a fly beats its wings, it makes a sound. But, if it beats its wings many times a second, those combined beats turn into a hum. The faster the wings are beaten, the higher the hum. If Robert Hooke’s wheel made the same note as the hum of a fly, then the frequency of the fly’s wings could be deduced.

Incidentally, a fly flaps its wings about 200 times a second - which is about the same pitch as a G or G sharp below the middle C of a piano.

A century went by before the French physicist, Félix Savart, took the invention of Robert Hooke’s wheel further, increasing the speed of the wheel and, therefore, the frequencies of sound produced, as he explored the hearing range of humans. The Savart wheel was named after him, as was the musical interval, the savart. 1,000 savarts have the range of three octaves and a major third - about half the range of a modern piano.

You can see a demonstration of this instrument here - with a tune that neither Hooke nor Savart would ever have heard in their lifetimes!

Incidentally, Savart was also an amateur musician and, with his knowledge of acoustics, experimented with the sound of a violin made in the shape of a trapezium. The intention was to improve the tone production of a violin by giving its resonator a smooth surface rather than a curved one. Here’s an example:

Rotation is, of course, a key feature of mechanical music and we’ll see more examples of instruments using wheels to produce sounds. Benjamin Franklin’s glass harmonica is rather similar to the design of the Savart wheel, but, instead of teeth hitting a card, sounds are produced using friction. The glass harmonica comprises glass vessels arranged on a spindle. The performer touches the rotating glasses with moist fingers to produce a pure tone of a certain pitch - rather like running one’s finger around the rim of a wine glass.

Some instruments have sounds generated mechanically, but still require skill and musicianship to play them - for example, the glass harmonica above, or the pipe organ. Other instruments produce music automatically, without any real musical prowess from the person operating them. We’ll take a look at automatically generated sounds in the next chapters.