Later in the day Warburg came to my room holding in his hand the little ten-page reprint of Roentgen’s paper, asking me if I cared to read it, and if so, to please leave it on his desk after lunch. The pages had not been cut, so I cut them up the side and along the top, read the paper, and left it on his desk.
Early in the afternoon he came to my room in a rage. “Herr Wood, why have you cut these pages?” going on to say that he had borrowed the reprint from the newsstand on the corner (they were on sale all over Berlin, at ten cents a copy), that Roentgen would send him a copy, and that now he would have to pay the news dealer, as I had spoiled the copy by cutting the pages. I said that he had suggested that I read it, and that I couldn’t very well read it without cutting the pages. “Why not?” he replied. “You can read it this way” (holding his finger between the pages, spreading them apart, and peeking in from the bottom). “That is what I did”. I said I’d be delighted to pay the news dealer and keep the copy myself. “Good. You can do that”, he beamed. I still have the reprint!
Within a day or two the laboratory was humming with the buzz of the vibrating spring interrupters of every Ruhmkorff induction coil that could be found in the instrument cases. Everyone who could blow glass and had access to an air pump was busy making the pear-shaped glass bulbs, sealing in electrodes, and laboriously exhausting them with cumbersome mercury pumps, which were all that we had at the time. The laboratory had gone X-ray mad. We photographed our hands, mice, small birds, and all sorts of things. I wrote a long story of the discovery, illustrated with photographs, and sent it to the leading Chicago newspaper. This was the first account to reach America, with the exception of a five-line cable. It was returned by the editor saying that they had already published a full-page story in the Sunday issue, illustrated with photographs made by a South Side photographer, who had antedated and beaten Roentgen — he had photographed the insides of a piano through the case, the vitals of a typewriter through its tin cover, and other impossible subjects, all transparent fakes of course.
I remailed the article immediately to the Century Magazine; it appeared in the next number, and even with this long delay it was the first comprehensive communication on Roentgen’s discoveries to appear in America.
When the required laboratory experiments were finished, it was customary for the newcomer to ask some professor’s help in choosing a subject for research. But one or two ideas had occurred to me while reading, and I had found a corner in the attic of the laboratory that was ideal for private experiments. It was roomy and out of the way. Moreover, it was a storeroom for old apparatus and barrels full of discarded vacuum tubes and glass bulbs used by the celebrated Goldstein, some of whose discoveries on the discharge of electricity in high vacua had antedated those of Crookes in England.
I hunted up an old induction coil and storage battery and played for a few days with some of Goldstein’s old vacuum tubes, often reading his papers. Nothing was known at the time of the nature of electrical discharges in gases at low pressure, and there was much discussion about the temperature of the luminous gas in vacuum tubes, which had never been determined experimentally by a method free from objections. The typical discharge in a long glass tube containing, say, hydrogen gas at low pressure, and furnished with wire electrodes at each end which carry the current from a high potential storage battery of many hundred small cells, is a rose- colored column of light, broken up into disk-shaped stratifications, extending two-thirds of the way down the tube from the positive electrode, then a dark space in which the gas is nonluminous, though obviously carrying the electrical current, and finally a blue glow extending out from the disk which forms the negative electrode but separated from it by another and very narrow dark space. An unsolved question was the distribution of temperature in this complicated discharge. Were the luminous parts hot and the dark spaces cold, or was the temperature sensibly the same throughout the tube?
I told Professor Rubens I should like to investigate this question and thought that it could be done with a bolometer arranged in such a way that the instrument could be moved along the discharge when the tube was excited. The bolometer measures temperature by the change in the resistance of an exceedingly fine platinum wire when heated, and therefore requires two wires leading to a galvanometer and battery. “And how then will you move a bolometer about inside a vacuum tube?” asked Rubens. I thought it could be done by mounting the discharge tube on the top of a barometer tube, with the bolometer wire on the upper end of a narrow glass tube carrying the two wires and passing up through the mercury column of the barometer. The open end of the barometer tube was to dip into a tall glass jar filled with mercury, and the narrow tube, carrying the bolometer at the top and bent into a long U at the bottom, passed down through the mercury column and up through the jar into the outside air. By raising or lowering the exposed arm of the U, the bolometer could be made to traverse the discharge tube. Rubens thought the idea good, and spoke of it to Warburg, the director. I was given a small room to myself, with an air pump for exhausting the tube or changing the pressure, and the necessary electrical equipment. I found an old Goldstein tube in the attic, which was exactly what I wanted, and started setting up my equipment.
The investigation with the movable bolometer occupied me for the better part of three semesters, and turned out even better than I’d hoped, for I was able not only to measure the temperature in the main parts of the discharge but also to record its slight rise and fall, as the bolometer loop of thin wire passed through the luminous disks of the stratifications. This method of exploring the interior of vacuum tubes became standard practice and has been used in many subsequent investigations by others.
Wood’s account of the Berlin period is not confined entirely to laboratory research. There are two colorful spots, one having to do with getting stuck on a pinnacle during a vacation rock- climb in Switzerland, and the other telling of adventures with the ill-fated Lilienthal and his glider. The rock-climb comes first, and here’s what he wrote about it:
I’m no mountain climber, much less a rock-climber, but when we went up from Interlaken to the Schynige Platte, which commands a marvelous view of the Jungfrau, Mönch, and Eiger, I was intrigued by a curious rock rising like the tower of an old castle and aptly named the “Gummihorn”. It was gray in color and resembled old, rotten rubber.
Baedeker said its summit had been recently made “accessible to experts”. It rose abruptly from a green hill only a few hundred yards from the hotel, and I decided to have a look at it after lunch. It was about a hundred and fifty feet in diameter at its base and perhaps three hundred feet high, the walls being practically perpendicular. Finding a place with a slight incline from the perpendicular I commenced to crawl up, finding numerous toe and finger holds. About half way up I found myself standing on a narrow ledge possibly ten inches in width, and faced by a smooth perpendicular wall about six and a half feet high. A bit of rope hung over the edge, and I could see that the other end was fastened to an iron spike driven into the rock of a second ledge above me. This evidently represented Baedeker’s “recently made accessible”. Clinging to a crevice with my left hand, I took hold of the rope with my right and gingerly pulled. As I pulled harder, it broke at the point where it was in contact with the sharp edge of the rock. I nearly let go with my left hand, but managed to keep my hold. I looked down. The grass looked pretty far away, and I began to doubt whether I could find the toe holds for descent. Finally I decided to climb on to the top and be rescued by the fire department. I managed to pull myself to the next ledge by means of the iron spike, and from here on to the top found the climbing easier. A group of Germans on a neighboring hill raised their hats on their Alpine stocks and shouted Hoch! Hoch! when I appeared on the summit, but I was too much shaken to do more than give an indifferent wave in return. I managed to get down by a slightly less difficult path. It was comic-opera mountaineering in miniature.