In the spring of 1899 Wood conceived the idea of studying light waves through their analogy with sound waves — and of projecting drawings of the latter on a cinematographic screen. There were, properly speaking, no motion pictures in those days, but the primitive machine had already been invented, and Wood was the first to foresee its possibilities in connection with animated drawings[5].
He had been puzzling over what form the light wave must assume in some of the complicated processes of reflection, as, for example, in a hollow spherical mirror. It occurred to him that this question might be solved by making use of the analogy between sound and light. A German physicist named Toepler had devised an instrument by which it was possible to photograph the spherical sound wave given off by the “snap” of an electric spark. This wave is, in fact, a spherical shell of highly compressed air, which expands with velocity of more than a thousand feet per second. To catch it before it has passed out of the field of the camera, it must be illuminated by the light of a second spark which occurs at about one ten- thousandth of a second later. With Toepler’s instrument, he made a long series of photographs of sound waves undergoing reflection and refraction, as well as diffraction and dispersion. One of the photographs showed the reflection of a sound wave from a little flight of steps made of glass and placed beneath the spark. The echo from the flight of steps consisted of a train of waves and constituted a musical note of high pitch. This phenomenon, the conversion of an explosive sound into a musical note, can be verified by clapping the hands together in front of a flight of steps, if one is in the open air where no echoes from the walls or ceiling interfere with the observation of the musical note which is echoed back from the steps.
The reflection of these waves from curved surfaces was extremely complicated. He first worked out a geometrical method of constructing their forms from theory, as they went through their contortions. These evolutions he drew on paper in black ink, by the hundreds, and then photographed them one at a time in succession on motion-picture film, which had only just been put on the market. Next he obtained a machine for projection, and found that the method gave admirable results. The black line representing the sound wave moved along, twisting and folding back upon itself in curious ways, and gave a striking picture of what was actually also happening to light waves in the case of reflection of light under similar conditions. Practically all of the optical phenomena of reflection and refraction of light were reproduced by sound waves and could now be studied in a new way.
The results were communicated to scientific journals here and abroad. Also the daily newspapers, caring nothing about the analogy with light waves — which was the only thing Wood did care about — were excited by the novelty of “seeing” sound waves, and reproduced page after page of the photographed drawings.
In January, 1900, Wood received an invitation from the Royal Society of Arts asking him to come to London and deliver a lecture on his color photography at the February meeting. Then came a letter from the physicist, Sir Charles Vernon Boys, inviting him to present before the Royal Society his animated photographs of sound waves. There are many Royal Societies, Royal Astronomical, Royal Photographic, Royal Microscopical, Royal Society of Arts, and Royal What-Have-You, but there is only one Royal Society tout court — founded in 1660 and unquestionably the most important scientific body in the world. Professor Snow was greatly excited and took the matter up with President Adams, who took it up with the Regents of the University, and Wood was given a two months’ leave of absence.
Boys met him on his arrival in London, put him up at the Savile Club and the Athenaeum, and secured suitable “lodgings” for him just around the corner from the former. His lecture before the Society of Arts was on St. Valentine’s day, with Sir William Abney in the chair. But the great occasion was still to come…
The young American professor’s appearance before the Royal Society was scheduled for the following afternoon. Boys had finally located and set up a motion picture projecting machine, of which there were then only two in London.
When they entered the sacred portals, the Fellows of the Society were having tea in the noble assembly room from which they all presently proceeded to the auditorium. Lord Lister, the venerable father of antiseptic surgery, presided from a thronelike chair behind an elevated desk. The great gold mace of Cromwell’s time was brought in on a red velvet cushion and laid solemnly on the desk in front of the president. Cromwell had treated it with less formality, and his celebrated order, “Remove that bauble!” has echoed down the ages.
In the audience sat many of the great scientific celebrities then alive in London: Crookes, Dewar, Sir Oliver Lodge, and Lord Rayleigh. In a moment they would be listening to “a young man from Wisconsin”, who would be standing where stood Isaac Newton, Davy, Faraday, and all the great in Britain’s scientific history. But if you think all this overwhelmed our young man from Wisconsin, you don’t yet know him. Says he in his notes: “I showed them the sound-wave photographs and moving diagrams without a hitch and spoke extemporaneously, feeling no more embarrassment than when lecturing to my students at Madison”.
Nonsense! Actually, he was acutely aware of the tremendous honor, and he was undoubtedly boiling with excitement. For it was the dawn of world-wide fame.
Chapter Eight.
Early Years as a Professor at Johns Hopkins — Great Discoveries and Promethean Celebrations
Following the death of the great, gruff Henry Rowland at Johns Hopkins in 1901, Wood was offered and accepted a full professorship in experimental physics there. It was a high honor for so young a man, no matter how fantastic a genius. Gertrude went ahead to Baltimore and selected a house on St. Paul Street in a city block that had looked upon the stoning by secessionists of the Massachusetts regiment on its way to Washington. Returning to Madison, the furniture was packed up and sent on in care of the Baltimore house agent, who installed it on its arrival. The family reached Baltimore late in September. They opened the Baltimore house, unpacked the crate containing the Stanley Steamer, and bounced over the cobblestones with which the entire city was then paved. Surface drainage disposed of all the water used for washing purposes, a thin stream, sky blue on wash day, running out under every back gate and along a shallow gutter in the brick sidewalk. Loose bricks acted as force pumps, squirting a jet of water up your trouser leg almost to the knees if you stepped on one, efficiently adjusted with respect to its neighbors. Wood called them “bath bricks”. The alleys and some of the street crossings had high stepping stones on which you crossed dry-shod in case of heavy rains, but at which the Stanley Steamer shied.
Of his work at Johns Hopkins, Wood says:
My teaching was very light, three lectures a week on physical optics, the same as at Madison, and I gave practically all of my time to research, a part of it in collaboration with graduate students working for the doctor’s degree. With J. H. Moore an investigation was made of the green fluorescence of sodium, with more powerful spectroscopes than the one I had used at Madison. This came along very well, an “infant phenomenon” being observed that became very important when it grew up in later years. Instead of illuminating the vapor in a small glass bulb with white light as I had done at Madison, we shot into it various colored rays in succession obtained by a combination of lenses and prisms called a monochromator, which sifts out from sunlight a very narrow region of the spectrum and projects the beam of pure color at any desired point. We found that when the metallic vapor was illuminated by a beam of blue light, it emitted fluorescent light of a yellow color, but as the color of the beam from the monochromator was changed to bluish green, green, and greenish yellow in succession, the region of maximum intensity in the fluorescent spectrum moved down towards the region of the exciting light and eventually coincided with it, with a suspicion of a trace of light on the further side of it. This was an exception to Stokes’s law of fluorescence, which stated that the light emitted by fluorescent substances was always made up of wave lengths longer than that of the exciting ray, that is, on the red side of it. Many years later unusual fluorescence was very clearly demonstrated in experiments that I made with sodium and iodine vapors, the discovery being of considerable importance in connection with the theory of molecular spectra.
5
Wood is frequently introduced to laymen by his scientific colleagues as “the grandfather of Mickey Mouse,” and a curious thing happened only last year (1940) in connection with Mickey Mouse’s Woodian ancestry. The AP carried a story that a professor at Wellesley had “applied the art and technique of Walt Disney” to the projection of animated mathematical drawings and curves. Mickey Mouse technique had completed the circle—beginning as a scientific abstract, and returning via Disney’s famous comics to its source.