Chapter Seven.
Wood Begins His Great Work with the Spectroscope — Becomes Grandfather to Mickey Mouse — and Lectures Before the Royal Society
Young Professor Wood’s early and final decision to make physical optics his special field came in a curious way, toward the end of his first year at Madison. Professor Snow had asked him to undertake a graduate course of lectures on that subject — which Wood had never studied before. He willingly agreed and began to bone up, keeping just a jump ahead of his classes at first. He says that when the bell rang at the end of the hour he had just about reached the end of his knowledge of the subject. But soon he began pulling ahead. He was reading the current journals of physics and found that marvelous new fields of optics were being opened up which were not treated in the textbook he was using, Thomas Preston’s Theory of Light. By the end of the year he had done enough independent study to realize that Preston was at least ten years behind the times. So he made his decision — he would make physical optics his specialty, and he would write his own textbook!
You will have to go a long way to beat that, I think, as a piece of sheer scholastic impudence. But the joker is that he did it — and that the monumental opus stands today, in its third revised edition and translated into German, French, Russian, and other languages, as one of the world’s standard books on the subject. The book was to take five years to complete, and was not to appear until Wood had gone to Johns Hopkins, but he immediately plunged into experimental work that was to get him world-wide attention and, in the local papers, the name of the Wisconsin Wizard.
Just what was the subject that Robert Wood was choosing? Physical optics is the scientist’s name for what he practices when he combines the resources of physics and chemistry to study and learn all he can of the nature, habits, and possible uses of light. In a sense it is a science that is as old as man’s first speculation of the cause of the rainbow; but as a modern science it may be said to date from Sir Isaac Newton, who first proved that a prism simply breaks white light into its component parts, which can be reassembled again into white light. For nearly two hundred years after Newton, scientists were preoccupied with the basic characteristics of ordinary light. They measured its velocity through space. They noted how light rays were bent when they passed through other media, such as glass, quartz, water, or colored solutions, and they formulated the laws of this bending, or refraction, to give us the telescope and the microscope. They noted how light passed through a narrow slit tends to spread out, and how no shadow, when minutely examined, shows a sharp break between black and white, and they named this phenomenon diffraction. They studied also the phenomenon of interference, in which one ray of light cancels out another and complete darkness results. By the middle of the nineteenth century they knew enough about light to know that light, heat, electricity, and magnetism were allied phenomena: they were waves of energy radiating in a hypothetical medium called the ether, and they differed from one another only in their wave lengths and their frequency of vibration.
The classical theory of light had thus been rounded out long before Wood came on the scene. But vast new possibilities in physical optics had been opened up in 1859 when the spectroscope came into use for detecting the chemical nature of substances. A spectroscope is nothing more than a prism mounted between a source of light and an adjustable eyepiece (or photographic plate) for accurate observation. The prism bends each color of light that enters it at a different angle; it is the spreading out (the scientist calls it dispersion) of the component parts of white light that gives you the rainbow or solar spectrum you see in a crystal chandelier or in a spectroscope when sunlight is passed through it. But Bunsen and Kirchhoff in 1859 discovered that if, instead of passing sunlight through a spectroscope, you used the light of chemical substances heated to luminosity, you got spectra of an entirely different kind, and that the substance could be identified by its characteristic spectrum (Wood had identified the origin of the boarding-house hash by just this method).
This discovery made the spectroscope one of the major instruments of modern science, and opened almost illimitable fields for physical optics. For light became not only something to be examined in itself, but a powerful tool for examining the nature of the physical world. The minutest traces of substances revealed themselves in their spectra; and the most distant nebulae and stars showed their composition — and even their velocity and direction — in their spectra. The subject became more complicated as it developed, for it was found that the same substance gave different spectra depending on the physical state in which it was. Thus the analysis of spectra revealed not only the chemical composition of substances, but the physical condition in which they existed as well. And different types of spectra were investigated: the emission spectra of luminous bodies, and the absorption spectra emitted when light of various kinds is passed through non- luminous liquids and gases. With all this development, the task of the scientist in physical optics became that of subjecting light to every conceivable kind of test to make it tell more of its nature and the nature of its source. He studied the emission of light by luminous bodies under various types of excitation, such as sparks, electric arcs, and gases at low pressure in vacuum tubes carrying an electric current. He examined fluorescence, or the emission by certain substances of light of a different color from that of the light played upon them. He placed the source of light in powerful electric and magnetic fields. And he carried his investigations beyond the bounds of visible light to the region of the infrared and the ultraviolet and X rays.
FISH-EYE VIEWS: Photographs Wood made with his “fish-eye” camera (see here). Top: the first outdoor photograph taken – a railroad trestle seen from directly underneath. Bottom: a photograph Wood took of himself in the window of his laboratory, by putting his camera at the end of a six-foot plank and working the shutter by remote control.
MORE FISH-EYE VIEWS. Top: the camera is on the ground and a group of men stand in a circle around it. A group of fishermen standing around a small trout pool would look something like this to the trout looking upward from the bottom of the pool. Bottom: a photograph of McCoy Hall at Johns Hopkins, taken from across the street.
When Wood came on the scene at the end of the nineteenth century, physical optics was in this exciting stage of evolution. And physics in general was in one of its greatest transitional stages — the stage between the atom and Newtonian physics and the electron and Einstein. Wood’s role was to be the daring experimentalist whose work would continually challenge the formulations of the theoretical and mathematical physicists, and thus bring them closer to the ultimate truth. And equally important, his experimental demonstrations would confirm the truth of many of their purely theoretical conclusions. His first major contribution to physical optics is a beautiful example of this — and also an example of the amazing scope of his special field of science. Here is his account.