In 1843 in England the Scottish engineer, Alexander Bain, invented a device using a paper soaked in an electrolyte which decomposed when exposed to a transmitted electric current. Bain’s original device consisted in a metallic stylus drawn upon a rotating disk (not unlike a record player) with a paper, wetted with a solution of potassium ferrocyanide, laid onto the disk Fig.1.
The stylus is connected to the telegraph circuit and as the current flows through the stylus it decomposes the solution leaving a continuous stripe of Prussian blue upon the paper. Obviously, if the current is switched on and off at regular intervals the stylus leaves marks of different lengths in a spiral pattern upon the paper. Another, earlier, form of automatic telegraph, which used a long ribbon of paper running over a roller, was developed from Bain’s system. As the current might be made to flow through the wires with a telegraph key (a Morse key) the stylus would then leave a sequence of marks along the length of the paper strip which could be read according to an agreed code of short and long lines not unlike the Morse code. If, at the transmitting station, the paper was punched through by a stylus and then run over the roller so that a wire alternately runs over the uncut paper or protrudes through the hole in the paper making contact with the metal surface of the roller and thus connecting the current to the telegraph wires, an automatic telegraph could be established.1
Bain’s chemical telegraph led to an important new idea: that an image could be transmitted via the telegraph by scanning it in 2 dimensions, originally as a spiral of lines reproducing the short and long pulses of the telegraphic code produced on a rotating disk (Bain’s version) or drum (Bakewell’s version) and shortly thereafter as a series of horizontal scans, each one placed below the previous as in Giovanni Caselli’s Pantelegraph [Fig.2]. Using Bakewell’s copying telegraph, if an appropriately cut insulating sheet of paper were placed on the drum of the sending station it could read out a helical scan of a handwritten document or image and transmit the scan to a synchronised receiving cylinder with an electro-chemical “writing” stylus which made marks in prepared paper according to the “pulses” in the current being transmitted.1 Obviously synchrony between the sending and receiving stations was necessary, and synchrony proved very hard to maintain.
The instrument developed by Caselli in 1860 used a metallised paper written upon with a greasy (and thus insulating) ink. As a steel or copper pen is drawn across the paper at the sending station, it either conducts and no current (signal) is sent or it is prevented from conduction by the insulating greasy ink and a current is then sent to the receiving station where a sheet of paper chemically sensitised to the current will be marked. By allowing the current to decompose the chemicals in the damp paper a piece of tin-foil laid behind it will carry a copy of the image which can then be chemically fixed. The scanning of each pen is kept in synchronism by a pendulum driven by electromagnets which are switched on and off by a very well regulated clock. The sychronism thus depended on the stability of the separate clocks at the sending and receiving stations [Fig.2]. Supposing that synchrony was well maintained it is clear that by tracing a series of parallel lines Caselli’s pantelegraph, was able to transmit not just letters but also designs.2 [Fig.3]
Caselli was aware that his pantelegraph could readily be used for non-European languages, while: “Oriental languages, and particularly Chinese and Arabic, [are] not available on other autographic telegraphs.” The Emperor of China heard about Caselli’s device and sent two diplomats to Paris for demonstrations of it in 1863.3 They are said to have been amazed that the pantelegraph could easily transmit Chinese characters and negotiations to take one back to Beijing were commenced but ultimately this project collapsed.4
Another version of this scanning concept was developed by the Italian Bonelli. He set up a message in movable type in a box and scanned it with a comb of 5 wires insulated from each other. As they connect with the raised portions of the type-face they would switch on a current which was then transmitted along a five wire telegraph system. On reception, a copy of the set up type is produced by running a similar comb of parallel wires over chemically prepared paper in the manner of Bain’s system.5
These developments led to the facsimile transmission of images which, while spawning both the “wireless photo” used in newspapers for most of the 20th century and the facsimile machine using the telephone, reached its zenith in the raster scan of the television set and the computer monitor, long foreshadowed by the Jacquard loom. It is also the basic concept behind all versions of the dot matrix or inkjet printer. In an interesting departure from the regular transmission of messages Lardner notes that music was also transmitted as fast sequences of pulses encoded into a paper tape at a telegraph office in New York.6
The display of waveforms
While the woven portraits and ribbons of the Jacquard-controlled loom were of great popularity as images, especially in the production of souvenirs, they could not particularly advance scientific education or experimental purpose. It is to those matters scientific that we should turn briefly by looking at the display of waveforms in acoustics and electricity.
The study of Acoustics and of the way the ear is induced to discern sounds was advanced both by Ernst Chladni and by Felix Savart.
Chladni began his work in Germany with his New Discoveries in the Theory of Sound published in 1787,7 which was later considerably extended in his Acoustics of 1802.8 They both invented means for displaying the shape of the vibrations that a sound made in a solid material. Chladni’s technique was to spread fine sand over the surface of a square or circular horizontal metal plate clamped to a stand. Then by drawing a violin bow across its edge the plate was caused to vibrate [Fig.4]. The vibratory motions of the plate would kick the sand into the air and then as it settled it would become aligned with the least active regions of the vibrating surface, forming exquisite patterns that showed the way the sound wave had spread across the metal plate and reflected off its edges.9 If the plate was circular the sand settled into radial patterns and if the plate was square the sand settled into rectilinear patterns. [Fig.5]
Around 1822, Felix Savart tried making the Chladni figures on an elastic membrane. He
“stretch[ed] a thin sheet of paper, about four or five inches in diameter, over the mouth of a vessel, such as a large glass … so that the paper has an uniform degree of tension and a horizontal position. A thin layer of fine and dry sand being scattered over the paper, a plate of glass in a state of vibration, is brought within a few inches of the membrane. The vibrations of the glass plate are conveyed through the air to the paper membrane, and the sand on its upper surface is thrown into figures which have sometimes the most perfect regularity”7 [Fig.6].
Savart applied these experiments to the mechanism of the tympanum of the ear (eardrum) showing that the tympanum vibrated in unison with the pressure waves acting upon it, and thence communicated these vibrations to the cochlear via the small bones of the inner ear.8
The Chladni figures became rather famous as a demonstration of the power of the invisible and achieved a certain notoriety as a semi-mystical phenomenon; making the invisible visible, being repeated in the 20th century as the Cymatic figures9 of Hans Jenny and being adopted as supporting theories of so-called “vibrational medicine”.
Charles Wheatstone, whom we have already met in the page on the Telegraph, spent a considerable period studying acoustics, light and electricity. He was a friend of Babbage10 and had recommended to Ada Lovelace that she translate the Menabrea memoir on Babbage’s Analytical Engine.11 Besides inventing the electric telegraph with Cooke in 1837 and the stereoscope in the early 1830’s he was also interested in the visualisation of sound. He built two devices that could show the vibrational behaviour of sound waves. The first was the Kaleidophone, which consisted in a stiff rod bolted to a stand with a silvered bead of some sort glued to its free end so that when it was set vibrating the light reflected from the bead would form a continuous line whose extent was determined by the rate and energy of the vibration.12 The continuous line is brought about by the persistence of vision.
Wheatstone’s other device was his Wave Machine.13 This was designed to demonstrate the basic behaviour of light waves and could also be used to demonstrate the behaviour of sound waves. Two sets of 80 parallel wires with white beads on the ends were mounted at right angles to each other and set into parallel slots in the sides and the top of the device so that when a “slider” was run through the machine the beads would move up and down as the molecules of water do in a wave or the particles of the “ether” were then believed to do in the transmission of light. Holland notes that “It could demonstrate the formation and propagation of any wave, the superposition and interference of waves of equal wavelength, and also the superposition of waves of unequal wavelength.”14 This instrument was primarily an educational or demonstration device. There is one in the School of Physics at the University of Sydney.
At least two methods of recording a visual trace of the waveforms of sounds were developed. One, the Vibroscope, invented by Jean-Marie Duhamel, a French mathematician, involved attaching a quill or a wire to a tuning fork. The free end of the wire was then placed against a smoked paper glued around a cylinder. Upon the cylinder’s rotation the wire scratched away at the smoked surface as it was vibrated by the tuning fork thus tracing the sound wave [Fig.7].
At least two methods of recording a visual trace of the waveforms of sounds were developed. One, the Vibroscope, invented by Jean-Marie Duhamel, a French mathematician, involved attaching a quill or a wire to a tuning fork. The free end of the wire was then placed against a smoked paper glued around a cylinder. Upon the cylinder’s rotation the wire scratched away at the smoked surface as it was vibrated by the tuning fork thus tracing the sound wave [Fig.7].
The second, the phonautograph invented by Leon Scott de Martinville, is modelled after the human ear, having a funnel that collects the sound which vibrates a membrane (as in the eardrum) with a stiff bristle attached to this membrane which scratches away at a smoked paper around a rotated cylinder. Invented in 1857, the phonautograph is often said to be the first sound recording device,15 which in a loose way it might be, but it was unable to reproduce the sounds it recorded, a process achieved some twenty years later by Edison. However the trace itself [Fig.8] is not dissimilar to the trace recorded by Edison onto a wax cylinder. In both the vibroscope and the phonautograph the smoked paper, was fixed by dipping the paper into ether.16
The Harmonograph
Another aid for making the vibrations of sound available to the other senses was the use of the harmonograph, a device that records the curve of the compound swing of two pendulums set at right angles. A pendulum when caused to swing will move from its initial somewhat rotatatory movement until it settles into a linear back and forth movement whose period is set by the length of the pendulum‘s string. The length of the swing will then settle back to zero as it uses up the potential energy imparted to it by the initial cause. The earliest form of harmonograph was devised by Blackburn in 1844 [Fig.9]. He hung a short pendulum from a transverse string [A,B in the figure] so that it pulled the string down by its weight. When the pendulum bob is pulled away from its neutral centre position it will swing with two components, one established by the length of the pendulum from its supporting string [C,D] and the other established by the length of the short pendulum [C,D] plus the distance [C,E] that it pulls the supporting string way from a line [A,B] drawn between the two supporting points of this transverse string. Thus the pendulum bob will swing in a compound way and if a container of sand, say, with a hole in it so that the sand drains out slowly, is used as the bob then it will draw the compound curve of the relationship between the two pendulum periods.17
An harmonograph made from two pendulums, set up so that their swings are at right angles to each other and allowing independent adjustment of their frequency and phase, was invented by S.C. Tisley in 1874 in the UK. [Fig.10].
One of the pendulums moves a drawing tablet and the other moves a pen set to draw directly onto the tablet, so that as the pen is moving back and forth in one direction the drawing tablet is moving at right angles to it. The compound curve so produced is a drawing of the frequency and phase relationships of the two pendulums.18 The drawings were considered quite beautiful and the harmonograph became a popular parlour instrument in the last quarter of the 19th century. [Fig.11]
Lissajous figures
Meanwhile, in 1857, the French mathematician, Jules Antoine Lissajous, had invented an optical means for observing the harmonic relationship between two tones. He used a pair of tuning forks set up at right angles with small mirrors attached to reflect a beam of light. One tuning fork is set in the horizontal plane and the other in the vertical plane and at such a relationship to the first that the beam of light reflected off the first onto the second and then onto a screen of some sort.19 [Fig.12]
If the two tuning forks possess an identical frequency then the compound trace reflected onto the screen will be a circle, supposing they also have the same amplitude or an ellipse if the amplitudes are not equal.20 If the frequencies of the two tuning forks are different then the compound curve will be a function of the ratio between the frequencies.
Quite complex forms can be generated with appropriate selection of the frequency ratio and the relative start timing (phase relationship) of the vibration (or oscillation) [Fig.13]. The best known Lissajous figure for us in Australia is of course the ABC’s logo which is a simple 3:1 ratio sine-wave based figure.21
One of the uses of the Lissajous figure was to assist in the tuning of tuning forks against a standard fork. In the mid-20th century the effect became useful in setting the frequencies of oscillators in electrical engineering. When a standard tone is connected to one axis of an oscilloscope (say the x-axis) and a test tone, of similar frequency and amplitude, is connected to the other (the y-axis) then the test tone can be tuned to an exactly matching frequency as the standard tone by watching the circle (or ellipse) the two tones produce when mixed in the oscilloscope. If it is moving then the two tones have a different frequency, if it is steady then the tones are of the same frequency.
Both the Lissajous figure and the harmonograph reappear in the mathematical art of early computer graphics and other experiments that led to various forms of interesting graphics based on mathematical curves, such as the harmonograph built by John Hansen Fig.12, early computer art using a plotter by Doug Richardson, and such complex forms as the Spirograph which appeared in a Meccano version built by Alan Bromley. John Hansen, at this time was working largely in his own in Melbourne, while the latter two were both at the Basser Department of Computer Science in the University of Sydney. However as I have indicated above, the visualisation of waveforms subsequently became the function of the cathode ray tube invented by Ferdinand Braun from work done by Crookes and Thompson.
———————————————————-
Return to Contents
FOOTNOTES
- Sabine, (1867), op cit, p.179. ↩︎
- Deschanel, (1872), op cit, pp.730-33. ↩︎
- See: < https://books.google.com.au/books?id=mnpeizY0btYC&pg=PA84&lpg=PA84&dq=Emperor+of+China+heard+about+Caselli%E2%80%99s+device&source=bl&ots=zvzFDiH-zg&sig=ACfU3U0Fi6yem22Pn24Q-5evzUJ981sa_Q&hl=en&sa=X&ved=2ahUKEwjMvcXimLSEAxXXsVYBHTKCDO04ChDoAXoECAIQAw#v=onepage&q=Emperor%20of%20China%20heard%20about%20Caselli%E2%80%99s%20device&f=falsehttps://books.google.com.au/books?id=mnpeizY0btYC&pg=PA84&lpg=PA84&dq=Emperor+of+China+heard+about+Caselli%E2%80%99s+device&source=bl&ots=zvzFDiH-zg&sig=ACfU3U0Fi6yem22Pn24Q-5evzUJ981sa_Q&hl=en&sa=X&ved=2ahUKEwjMvcXimLSEAxXXsVYBHTKCDO04ChDoAXoECAIQAw#v=onepage&q=Emperor%20of%20China%20heard%20about%20Caselli%E2%80%99s%20device&f=false > ↩︎
- Feydy, Julien (1995) “Caselli’s Pantelegraph”, La Revue, Musee des Arts et Metiers, no.11, June 1995, pp.50-57, Paris: Centre National des Arts et Metiers. ↩︎
- Sabine, (1867), op cit, p.182. ↩︎
- Lardner, (1854), op cit, vol iv, p.71. ↩︎
- Savart, Felix, (1825) “On the Acoustic Figures produced by the Vibrations communicated through the air to Elastic Membranes” in Brewster, David (ed) The Edinburgh Journal of Science, Vol.II, November – April 1825. pp.296-301 ↩︎
- Savart, (1825), op cit, pp.300-1. ↩︎
- Also in this video there are some beautiful vibrational patterns (a la Chladni) to be seen. https://www.youtube.com/watch?v=KijiWlTJp3Y ↩︎
- Toole, (1992), op cit, p.112, note 4. ↩︎
- Woolley, (1999), op cit, p.259. ↩︎
- Brewster, (1868), op cit, p.252. ↩︎
- Holland, Julian (1999) “Charles Wheatstone and the Representation of Waves – Part II”, Rittenhouse, Vol.13, no.2, p.30. ↩︎
- Holland, Julian (1999) “Charles Wheatstone and the Representation of Waves – Part II”, Rittenhouse, Vol.14, no.3, p.30. ↩︎
- For some of the history see Wikipedia https://en.wikipedia.org/wiki/Phonautograph. For a picture of one in the Smithsonian Museum, see http://cylinders.library.ucsb.edu/history-early.php ↩︎
- Deschanel, (1883), op cit, pp.904-5. ↩︎
- Deschanel, (1883), op cit, pp.932-3. ↩︎
- Goold, et al, (n.d.), op cit, pp.4ff, or Poynting and Thomson, (1904), op cit, pp.75-8, who claim the harmonograph for one A.J. Donkin. ↩︎
- Deschanel, (1883), op cit, pp.927-30. ↩︎
- for the maths see Deschanel, 1883, op cit, p.930, notes 1 and 2. ↩︎
- http://abc.net.au/science/holo/liss.htm ↩︎