y small, but not the "very very" small. There are details of the structure of the living cell, essential features in the composition of metals, cotton, silk, rubber, paint, bone, nerve, and a thousand other things which are hidden even from the microscope, and must always remain so hidden because the failure does not lie with the skill of the optician but with the incapacity of light itself.
The nature of radiation is in many respects a mystery, but we know enough about it to understand that we may talk of it in many of its important aspects as waves in some medium which we call the ether. If the radiation falls on any object, it is turned aside and modified in various ways. When our eyes are directed towards the object, they take in the modified rays, and we have learned by long practice to know, from these modifications, the nature of the object that has made them. That is "seeing."
The central point of the process is the act of scattering and modification. Now waves have a certain wavelength, and common experience of such waves as may be seen, for example, on the surface of the sea tells us that an object which is very much smaller than the length of the wave has no appreciable effect upon it. In just the same way there may be objects which are so small that they can not affect a ray of light, and such objects are forever invisible in the ordinary sense. The length of the light wave which our eyes can perceive lies within a short range on either side of a fifty-thousandth of an inch.
The X rays break down the barrier for us, and admit us to this immense field in which we want to be. They do so by virtue of their character as light waves, 10,000 times or so smaller than visible waves, but of exactly the same nature.
If a substance is such that all the atoms which compose it are arranged on one and the same pattern, so that the straight rows run through from side to side, the substance is a single crystal; crystalline character meaning, simply, perfect arrangement. But most substances, and especially those we handle every day, such as the metals, must be described as masses of small separate crystals.
However we try to deform [a bar of multi-crystalline material], there are always some crystals which resist being deformed in that particular way. And the various crystals back each other up according to some principle which we do not fully understand. Thus the properties of the bar depend upon its crystalline character. It is only the X ray that can tell us the internal arrangement of the crystal.
The X rays are of short enough wavelength to be turned aside or scattered by the atoms, when longer light waves are not. A single atom can, however, do very little. Here is where the regularity of crystal arrangement comes in. The unit of pattern is repeated an enormous number of times even in a crystal just visible to the naked eye. Whatever one of these units does in the way of scattering, all the others do in regular order. The combined amount is perceptible, and so the crystalline character is detected.
Of course this is an indirect way of examining the structure. We do not perceive the individual atoms; we discover only their arrangements. But the knowledge so gained can be combined with other knowledge that we already possess and we have actually found ourselves able to decipher the patterns of Nature to an extent we did not dream of a few years ago.
The Bubble Chamber
By Donald A. Glaser (Nobel Prize in 1960)
Published February 1955
In their exploration of the submicroscopic world of atomic nuclei, physicists are like men groping in a dark cave with a flashlight that goes on for only an instant and each time lights only a tiny corner of the cave. Occasionally the flash catches some activity or event—either a familiar particle behaving in a familiar way or some strange new particle whose behavior is altogether baffling. From these scanty glimpses nuclear physicists are attempting to identify the particles and the forces at play in the dark, violent world of the nucleus of the atom. It would help if they had a better flashl