As further examination of detonators showed that they contained nothing of the nature of this solid bullet, it was clear that it had been molded by the heat and pressure of the explosion from the paper-thin wall of the copper detonator tube. This discovery, for it really was a discovery, shows the importance of experiment in any investigation. Up to this time the formation of this solid pellet had never been noticed or described. Its formation resulted from the presence of the dent at the bottom of the copper tube, which the explosive experts had found increased the force of the dynamite exploded by the detonator without knowing why. The reason was now quite clear. The copper bullet traverses the entire length of the dynamite stick, with an initial velocity three times that of a rifle bullet. If there were only the thin fragments of sheet copper into which the rest of the detonator is blown the explosion would be started only at one end of the stick.
The problem of how this solid pellet was formed was solved by firing detonators loaded with different amounts of explosives into a long cylindrical pasteboard tube filled with cotton, diaphragmed with thin paper disks every two inches, the pellet being searched for in the cotton lying between the last disk perforated and the next intact disk. As the pellet, which starts off with an initial velocity of about 6,000 feet per second, penetrates the cotton it gathers a tightly wadded ball around it as it advances, spinning its own cocoon, so to speak, and is thus protected from friction against the matter through which it is passing.
Until Dr. Wood made these discoveries, not even the technical experts on dynamite, blasting, and commercial explosives had ever known or dreamed of the terrific velocity this “pellet” expelled from the detonator possessed, much less the weird, sinister shape into which it became transformed.
These detonators, harmless-looking as an ordinary small cartridge, yet as deadly dangerous as rattlesnakes — often picked up by children around quarries — began to interest Dr. Wood. He learned that there are between three hundred and four hundred accidents from detonators per year in the United States, many of them fatal. He continued his experiments and issued warnings, which have already begun to cut down this category of accidents in which children are frequently injured, mutilated, blinded, and have in some cases lost their lives.
Said Dr. Wood: “Children fire them usually by putting them on a rock and striking them with a hammer or another stone. Parents and schoolteachers should warn children that if they ever find anything resembling a twenty-two-rifle cartridge with wires or a fuse protruding from it, they should give it a wide berth and should on no account attempt to explode it”.
Wood’s most far-reaching, though less sensational, contribution to the science of detection is known, curiously enough, throughout the world as the “Vienna Method”, though it was invented in America, by an American, and given first to the American police. It is a device for detecting raised checks, superimposed forgeries, erasures and alterations in manuscripts, by photographing the material with ultraviolet light. Wood published the method about 1906; the alert Vienna police began to read about it, and wrote direct to Wood for further details, which he generously supplied, with additional suggestions. They then began publishing extensive reports in various important technical European police journals, giving Dr. Wood full credit for the invention but claiming its adoption by themselves. In consequence, even here in America, “Vienna Method” became the police-laboratory name for it.
Despite his major absorption in pure science at Johns Hopkins, Dr. Wood is still frequently called on by both the police and private parties to help solve this or that mystery — particularly if it has anything to do with fires or explosions.
Not long ago two lawyers, accompanied by a gentleman whose left hand was missing, knocked at the door of Wood’s laboratory. It was explained that a serious accident had occurred on a turkey hunt. A shotgun had exploded at the breech, tearing off the hunter’s left hand at the wrist so completely that it hung by a few shreds of muscle and skin. The gun was one of the most expensive on the market, guaranteed by one of the most prominent firms dealing in firearms, and the victim was about to bring suit against the company for heavy damages. A chemist who had analyzed a fragment from the barrel was ready to testify that it was made of a low grade of steel and showed evidence of flaws, but the lawyers wanted someone who had specialized in explosions to serve also as expert. They had brought the gun with them, a twelve-gauge shotgun of aristocratic family.
Wood examined it carefully. The explosion had occurred in the barrel at a distance of about three inches from the breech, and at first sight he could not understand how such a serious break at this point could have been caused by a normal cartridge.
After examining the inner surface of what remained of the barrel with a magnifying glass, he laid the gun down and said: “Gentlemen, you’ve assigned me to the wrong side of the case. The explosion was due to the circumstance that somebody had slipped a sixteen-gauge shell into the twelve-gauge gun by mistake. It had slid into the barrel and stuck where the barrel narrowed above the breech. Subsequently a twelve- gauge cartridge had been introduced and fired. The simultaneous explosion of the two cartridges exploded the barrel”. Wood pointed out that bright, brass-yellow stains could be seen at several spots on the inner surface of the barrel, and taking a penknife he succeeded in detaching two small fragments of thin sheet brass, which had been welded to the steel by the force of the explosion. These fragments had exactly the thickness of the sheet brass from which the head of a sixteen- gauge cartridge is made.
There was an uproar. The owner of the gun insisted it was impossible. He had no sixteen-gauge shells in his pocket, did not even own a sixteen-gauge gun. He had fired the gun a few minutes before the accident, had inserted another twelve- gauge immediately, and closed the breech.
Wood said, “I can’t help that. A sixteen-gauge got in somehow. Someone in the gun club may have picked up a shell that had been dropped on the floor and put it in the pocket of your hunting coat that may have been hanging in the vicinity. You slipped it into the gun after firing, and then a few minutes later, not being sure whether you had reloaded or not, opened the breech, and seeing that it was empty (the sixteen-gauge having slipped down out of sight) you inserted the twelve-gauge”.
The owner was aggressively positive about the impossibility of such a fantastic theory. He remembered exactly what he had done, and after a long argument the group departed. Wood noticed that the two small fragments of brass were still on his desk, and he put them carefully in a pillbox and tucked them away in his desk drawer, in case they should be required subsequently.
The lawyers, however, still wanted his testimony in regard to certain other facts connected with the explosion, and pointed out that only such questions would be put to him as could be answered without reference to the yellow metallic stains and fragments of brass. But Wood declined to go on with it. “The other side may employ an expert who will notice the stains, and their counsel will ask me in cross-examination if I didn’t observe them, and I will either have to commit per jury and say ‘No’ or give a truthful answer, and then be faced with the question: ‘Did you point this out to the prosecution?’ ”