Wood doesn’t guess at the answer. Kimura was an extremely intelligent and popular fellow, and knew from experience that he was always welcome at the fireside.
Not much came of these lunar experiments (says Wood), chiefly because of climatic conditions. Dew formed on the mirrors, the clock did not drive very steadily, and there were innumerable mosquitoes, who came from all directions to see what was going on. So later in the autumn through the courtesy of Professor H. N. Russell of Princeton University, I was given an opportunity of mounting my sixteen-inch mirror at the Princeton Observatory. Professor Harlow Shapley, now director of the Harvard Observatory, was then a fellow in astronomy at Princeton, and he assisted me in handling the telescope and making the exposures.
We made photographs of the full moon by orange, violet, and ultraviolet rays, the latter bringing out the dark deposit bordering the lunar crater Aristarchus with great distinctness, while the orange-ray picture showed no trace of it. Experiments showed that when a gray volcanic rock was treated at one spot by blowing a jet of sulphur vapor against it, a thin deposit of sulphur crystals was formed which was invisible to the eye but came out black in a photograph made with ultraviolet rays. It therefore seemed probable that an extensive deposit of sulphur had been found on the moon’s surface by the new photographic technique.
The plates obtained through the ray filters could be studied to advantage by the methods employed in the three-color process of color photography. The negative taken through the ultraviolet screen was printed on a gelatin film and stained blue, the violet and orange pictures being rendered in red and yellow respectively. The three films when superposed resulted in a very fine color photograph which brought out the differences in the reflecting power of the different dark areas on the moon in a very striking manner. The prevailing tone of the darker portions of the lunar surface was olive green, but certain spots came out with an orange tone and others with a decided purple color. The dark spot near Aristarchus came out deep blue, as was to be expected.
INFRARED LANDSCAPE: A 1911 photograph made by Wood of a summer landscape in Sicily – the earliest landscape photograph with infrared light ever made. Wood also pioneered in ultraviolet-light photography.
PEGOUD UPSIDE DOWN: Wood pirouettes in the snows of St.Moritz, in the constume he designed that won first prize at the fancy dress ball.
In 1911 Wood also continued his researches with mercury vapor and detected resonance radiation in the ultraviolet region, analogous to the sodium vapor resonance at the yellow lines. The thing of greatest interest was the invention of what he termed a resonance lamp.
A thin-walled bulb of fused quartz was blown, a drop of mercury placed in it, the air pumped out, and the bulb sealed. The mercury vapor in this vacuum bulb had sufficient density at room temperature to emit resonance radiation when illuminated by the light of a quartz mercury arc, operated with weak current at low temperature. The radiation was powerful enough to make a screen of barium platinocyanide glow with a yellow light, and if a drop of mercury was supported on a slightly warmed bit of glass between the screen and the resonance lamp, the vapor rising from the drop showed as a waving, fluttering column of black smoke on the yellow background. This made it possible to design an optical apparatus that would show the slightest traces of mercury vapor in the air of the room, a matter of importance in power plants where the engines are driven by the vapor of mercury instead of by steam. The vapor is very poisonous, and a very small leak in the high- pressure boiler or engine might exist undetected until the men showed symptoms of mercurial poisoning, by which time permanent damage would have been done. Several years later the General Electric research laboratory asked Wood to design apparatus for this purpose. He went to Schenectady with drawings, but they decided not to use it, as their chemical staff had prepared a paper that would turn black when exposed to the vapor. After getting along with this for several years, they found, according to report, that the paper was sluggish in its action, and might not respond to a sudden leak before a dangerous dose of the poison had been inhaled. One of the young men in the laboratory was then given the problem of making an optical detector along the lines suggested by Wood. After he had worked a year without results, Wood was consulted by an older member of the staff. It turned out that all that had been done was to try to detect the absorption of the vapor by the light of a high-pressure, high-temperature quartz arc. Wood pointed out the foolishness of this attempt, since practically no light capable of being absorbed by traces of the vapor is emitted by such a lamp, for it is all absorbed by the cooler layer of vapor surrounding the arc proper in the tube of the lamp. They were instructed to use a resonance lamp, or an arc operated at very low temperature, and within a year the papers were full of the “electric nose” for smelling mercury vapor in the air, developed by engineers of the General Electric Company. It was identical with Wood’s first suggestion, except that it was arranged to ring a bell, instead of showing the presence of the vapor by a difference of luminosity in the two halves of a circular phosphorescent screen, a mere matter of using a photoelectric cell and amplifiers.
In the early part of 1913, Wood was invited by Sir Oliver Lodge, chancellor of the University of Birmingham, England, to attend the annual meeting of the British Association in September — and to receive the honorary degree of Doctor of Laws from the university.
As they were planning to take a second sabbatical year abroad at about this time, Wood accepted the invitation and went on ahead to England, while the rest of the family proceeded to Paris.
Sir Oliver Lodge was president of the British Association that year, and the meeting was the largest since 1904. Among others who were to be presented with LL.D.’s at the same meeting were Professor H. A. Lorentz and Madame Curie. In presenting Wood for the LL.D., Sir Oliver characterized him as “one of the most brilliant and original experimental physicists in the world”.
In his own address at the meeting, Wood described experiments with resonance spectra and amused the distinguished gathering with an account of his use of the family cat to clean the spectroscope. Nature, in reporting his speech, was even more glowing than Sir Oliver had been in his presentation. A little later Frederick Soddy, subsequently professor of inorganic chemistry at Oxford, referred to Wood in the same journal as “one of modern experimental research’s greatest masters”.
Wood still found time to enjoy himself. Before he left England, he went out to the great automobile race track at Brooklands for the races, where he also witnessed a stunt that set the aeronautical world agog. Pegoud, the French aviator, was to do his new and famous act in which he not only looped the loop “outside” as well as “inside”, but actually flew upside down for a quarter of a mile. “It was a lovely autumn day”, says Wood, “and the great stadium was packed. There came the hum of a motor high up in the air and we saw the tiny aeroplane with Pegoud’s helmeted head showing above the cockpit. A loop, another and another, and then the plane flying on a horizontal path, upside down with Pegoud’s inverted body hanging by the straps. The crowd of twenty thousand came to its feet with a gasp and a prolonged ‘A-a-ah.’ The plane dived again, turning over, and sailed along right side up with Pegoud now only a hundred feet above the ground waving to the cheering and shouting spectators”. Wood was tremendously pleased with the show, and later made amusing use of his impressions.