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And now comes Professor Roentgen with the discovery that from this arrangement described there proceeds what is believed to be a kind of vibration more distinct from the other sorts than the Hertzian waves are from light. No sense can perceive it, and it is being recognized and studied by its effects, noticed now for the first time. It illustrates how little man is capable of perceiving. This was the way Professor Sanford talked over his Crooke’s tube:
“There are many peculiar phenomena which take place in Crooke’s tube, and they have been studied for about fifteen years. If the air is entirely exhausted, there can be no spark produced in one. They are generally exhausted to from the one-thousandth to the one ten-thousandth part of an atmosphere. The end of the wire connected with the negative pole of the battery is called the cathode, and the effect appears to proceed from the cathode. When the current is started the particles of rarefied gas are electrified and driven off from the cathode with great force.
“If there is sufficient gas it becomes luminous through the particles striking each other. When the particles can reach the walls of the tube and pound against them, they set up a fluorescence in the glass. Probably they cause the glass to set up light vibrations in the ether. The cathode rays are not the X rays of Roentgen, nor are they rays of light. They are the steams of gas particles as they are repelled from the cathode, and it is rather their effect which is talked about.
“If I put certain substances near this tube, they will likewise fluoresce, as has been known for some time. It has not been known that the cathode rays would produce the same effect when the fluorescence was hidden, though it had been discovered that when a tiny sheet of aluminum is set in the tube like a pane of glass the cathode rays striking on this opaque window would produce a fluorescence in a proper substance placed behind it.
“Roentgen accidentally discovered in his laboratory that a sheet of paper moistened with double cyanide of barium and platinum and left near a Crooke’s tube when the tube was covered with a black cloth would show fluorescent effects, showing that the cloth was transparent to the cause of the fluorescence. He followed this discovery with his experiments. The effects secured can hardly be explained by any knowledge or theories held before. The rays from the Crooke’s tube, which produced Roentgen’s new fluorescent effects and later his photographic effects after passing through wood and flesh, are, of course, not light, and they are not Hertzian waves evidently. His theory is that the gaseous particles, striking against the glass, produce a vibration which sets up waves or vibrations in the ether different from any other kind of motion. He thinks that they are longitudinal ether waves.
“We have no sense that enables us to take cognizance of the ether as we can of light and heat, but we know that light and radiant heat are vibrations in an elastic medium, and we call that medium the ether. It must pervade all bodies, because some form of radiation can pass through all bodies at a velocity far greater than it would be if the bodies themselves transmitted it. The ether is as real to physicists as matter. We know only one kind of ether waves, and they are now all included in the term radiation. We know no limit to their lengths. One very small octave in the range of wavelengths we can perceive by the eye as light.
“Now, every kind of ether waves or vibrations that we know anything about can be reflected, refracted and polarized. We also know that all the kinds of ether waves with which we are acquainted are transverse vibrations; that is, the vibrations are back and forth across the line or plane of motion, like waves in water or in a rope when it is shaken, or like the vibrations of a string. When we speculate about Roentgen’s rays being longitudinal vibrations in the ether we mean that they are like sound vibrations, in which the vibrations are back and forth on the line of motion without crossing it. In sound vibrations the air goes out on a straight line, stops with a condensation and goes on again. Sound is the only kind of longitudinal vibrations we know anything about.
“It has been recognized by physicists that there is no theoretical reason why there should not be longitudinal waves in the ether, but it has been supposed that the ether was so nearly incompressible that the waves would have almost infinite velocity and length and hence could not be perceived. All elastic bodies, solid, liquid and gaseous, transmit, longitudinal waves, and as the ether is an elastic body it would certainly transmit them too. Roentgen has discovered that his new rays cannot be reflected, refracted or polarized, as we can do with all known kinds of ether vibrations. So Roentgen thinks that he has discovered a new kind of radiation. What longitudinal ether waves would do we do not know.”
An important find
“Whatever Roentgen’s discovery may be, it is an important find. Anything that will throw light on electrical phenomena is of value to science. We are calling on the ether to explain heat, light and electrical effects, and probably all effects which we class under chemical and magnetic attractions and repulsions, and even gravitation, as far as we have any hope of explaining it.
“It should be remembered that we have before produced photographs with electrical waves not luminous, and others have done to a certain extent what Roentgen has done and without the aid of light, except, we can refract and reflect the waves which have been presumed to produce the effects. In 1893, I produced photographs in the dark with the use of electrical waves, and I have attributed them to the Hertzian waves. It is barely possible that my pictures were due to the X rays.
“A great general misconception about Roentgen’s discovery and its possibilities would be corrected if it were remembered that his rays cannot be reflected by any thing, or refracted by a lens of any substance. Hence no image can be produced. The rays pass through substances transparent or translucent to them and cast shadows on the negative which are fixed there. It is wholly the fixation of shadows. The bones of the hand being opaque to the rays cast their shadow on the plate when the rays pass through the hand. The negatives used are prepared for the effect of light. Negatives better adapted to these rays may be expected to be invented.”
Page 1: Top photo — Early x-ray experimentation. Second photo — Early x-ray photograph by Wilhelm Röntgen of Dr vonKolliker’s hand (January 1896). Third photo — Wilhelm Röntgen portrait.
Page 2: Top illustration — Wills cigarette card of “X-ray apparatus” (c1902-1917), courtesy NYPL; Second — Public lecture flyer from London, 1896. “Before leaving the exhibition ‘see’ the wondrous X rays. The greatest scientific discovery of the age. By the aid of new light, you are enabled to see ‘through a sheet of metal’; ‘through a block of wood’ and also ‘count the coins within your purse.’ Admission 3d. Open all day. X-ray photographs taken.” Third — Drawing of Rontgen giving his famous X-ray lecture.