At the other end of the tunnel, which terminates in a dark room, is a small slit and back of that a mirror on which the sunlight is reflected from the outside by means of another mirror and a lens. This reflecting mirror and lens work as a heliostat revolving by clockwork, with the motion of the sun, so that the reflected light is always on the mirror at the dark end of the tunnel, which in turn always reflects this light through the slit to the achromatic lens and the diffraction grating. When the light is decomposed by the grating and sent back through the tunnel it is tilted slightly upward so that a photographic plate inserted just above the slit will take a photograph of the section of the spectrum on which the professor is working.
The wonderful power this instrument has in diffracting color and decomposing the spectrum is shown in many ways, each of which manifests its superiority over previous spectroscopes and the results obtained by them. In the first place, the professor said, in a small laboratory spectroscope what is known as the yellow sodium line appears as a single line, while in this new spectroscope this same line… appears as two distinct lines, separated by a distance of 5 inches!
Furthermore, the entire spectrum as seen by this instrument would be 50 feet long, while the finished spectrum magnified three times in order to study the various spectrum lines would be 150 feet in length. This is the length to which the spectrum studied by Professor Wood is extended, although he is not interested in the entire spectrum but only one part connected with his study and research work.
Professor Wood is now making a study of the absorption spectrum of iodine in connection with some other work along the same lines which he did last summer.
Despite the unwilling co-operation of the family cat, the wooden tunnel of the original East Hampton spectroscope became unsatisfactory. Wood had built a shingled roofing along its full length. But rains and snow finally wet and warped it. So he decided to build a new tunnel underground, using sewer pipe. East Hampton had a stone mason and pipe- layer by the name of Barnes, with whom Wood had been on terms of complete understanding since the episode of the baptismal font. There are various versions of that story too. Here’s what Wood tells me actually happened.
Barnes was doing some work for us while we were renovating the place, shortly after its purchase. He was building the cesspool. One day when our own car balked, I rode downtown with him on the seat of his cart, with barrels and sieves rattling behind. As we were passing through the village, the new rector of the chapel at Amagansett came hurriedly toward us, holding up his hand as a stop signal.
“Good morning, Mr. Barnes. I trust, Mr. Barnes”, he unctuously intoned, “that you will bear in mind that you promised to come to Amagansett at your earliest opportunity and lay our new baptismal font”.
“Yes, Doc”, replied Barnes, “I’ll build your baptismal font soon’s I can, but I got to finish the Prof’s cesspool fust”.
Barnes’s comeback had so enchanted Wood that he sent for him later to build the new spectroscope tunnel. The problem, of course, was to keep the tunnel, built of terra-cotta sewer pipes with walls of irregular thickness, absolutely straight and smooth inside. This was a problem that had never confronted Barnes before.
Wood put a heliostat (a mirror operated by clockwork) in the pit at the end of the forty-foot trench, which reflected a horizontal beam of sunlight three inches above the trench bottom. He told Barnes to lay the pipes along the beam of light, each pipe being adjusted so that the circular spot of light was exactly at the center of a sheet of white paper held against its end. When the job was finished and viewed from the outside, it seemed as full of irregular little humps and twists as a convulsed snake which had tried and failed to straighten out. Barnes said disgustedly, “That’s the worst job I ever did”. Wood said, “Look through it”. Barnes looked and said, “Gosh!”
It was straight as the bore of a rifle — on the inside.
JOHNS HOPKINS PROFESSOR: Wood in 1901, when he became professor of experimental physics at Johns Hopkins University.
THE MERCURY TELESCOPE: Here we see the spinning bowl of mercury reflecting the face of Wood as he gazes at it. Since the mirror is concave, reversing reflected images, Wood’s reflection appears right side up. This photograph was taken in the barn laboratory at East Hampton, where the preliminary work was done. Later the mercury telescope was moved to a pit under an adjacent cowshed.
Chapter Eleven.
Wood Turns His Sabbaticals into Triennials, Stands Where Faraday Stood, and Is All Over the Map
The average university professor is happy if he can take a full year’s sabbatical once in every seven years. But nothing is ever “average” with Wood. He took his first sabbatical in 1910- 11, another in 1913-14, went overseas again in a major’s uniform in 1917, then again soon after the armistice, and has been making long visits to Europe in intervals ever since. His growing international fame, his many invitations to lecture before learned societies abroad, his researches with European colleagues, the funds derived from the Adams endowment for publication of his work by Columbia University, the appreciation of Johns Hopkins, which always gave him half pay during absence, all contributed toward making these triennials not only possible, but reasonable.
Wood began his first so-called sabbatical in the summer of 1910, after devising earlier in the year a new type of diffraction grating which he named the Echelette.[9]
He went first to London, where he delivered the Traill Taylor Memorial Lecture, an annual function of the Royal Photographic Society, and the initial “Thomas Young Oration”, a similar affair just started by the Optical Society. He then joined his family in Paris. Elizabeth, now aged twelve, was placed in school there, and Robert, Junior, aged sixteen, at school in Geneva. Margaret, now a tall young lady of seventeen, accompanied her parents to Berlin.
In Berlin, the Woods found a pension facing the Tiergarten, near the school where Margaret chose to study art. Wood’s amateur talents in this direction had been increased in their transference to the daughter, who later made a name for herself as an outstanding portrait painter.
The family was now joined by their old friends, the Trowbridges. With Trowbridge, Wood attended the celebration of the hundredth anniversary of the founding of the University of Berlin. They went as official delegates from Johns Hopkins and Princeton. The ceremonies were elaborate. Kaiser Wilhelm was there in gorgeous uniform. With him was the pretty crown princess with whom, according to Trowbridge, the irrepressible Wood (delegate from Johns Hopkins!) carried on a mild flirtation during the tedious ceremony.
Soon Wood was deep in research with Professor Rubens, who fifteen years before had encouraged him to change from chemistry to physics. The research with Rubens was on a new method they had developed for isolating and measuring the longest heat waves ever discovered. It was at the time when efforts were being made all over the world to fill the gap in the spectral region between the longest infrared heat waves and the shortest electric or radio waves, for Maxwell’s theory showed that light and electromagnetic waves differed only in length. The method which they discovered was called focal isolation and depended on the odd circumstance that crystalline quartz was exceedingly transparent to a group of waves far longer than any discovered in the infrared, while having at the same time an index of refraction much higher than for visible light, in other words “anomalous dispersion”. They succeeded in isolating heat waves of over 0.1 of a millimeter[10], the longest observed at that time.
9
It was designed for work in the remote infrared region of the spectrum. These were coarse gratings having from 800 to 4,800 lines to the inch ruled with deep saw-tooth grooves in copper. Gratings for work with visible light have from 15,000 to 30,000 lines to the inch ruled on a harder metal, speculum, or aluminum on glass. He carried on a short research with Trowbridge at Princeton in which they examined the behavior and performance of the grating, incidentally resolving the carbon dioxide band at 4.3 μ into a double band, which had never been done before. They did not realize the importance of this discovery at the time, and their paper was overlooked by Bjerrum, whose theory of molecular band spectra published in 1912 predicted a double band in the infrared as a result of a vibration in the molecule combined with its rotation. The double band was rediscovered in 1913 by Eva von Bahr, to whom credit has always been given for proving experimentally the theory of Bjerrum. The band had been pictured and described in the Philosophical Magazine three years before. Bjerrum’s oversight was probably due to the tide of the paper: “Note on Infra-red Investigations with Echelette Gratings.”
10
Later on, using the same apparatus but employing a mercury arc lamp instead of the Welsbach, Rubens and Von Bayer isolated a radiation having a wave length of 0.3 of a millimeter.