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Updated: May 4, 2025
There was, however, a great difference between the discovery made by Röntgen and anything that had preceded it. His stage of progress in knowledge was this, that during the discharge of one kind of rays of force from the cathode pole in a Crookes tube another kind of rays are set free, which differ totally in their nature and effects from anything hitherto known.
Apparently they cannot be produced except in a very high vacuum, where the pressure of the air is about 1-100th millionth of an atmosphere, or that which it is some 90 or 100 miles above the earth. Mr Crookes regards them as a stream of airy particles electrified by contact with the cathode or negative discharging point, and repelled from it in straight lines.
He held that the heat and phosphorescence produced in a low-pressure tube were caused by streams of particles, projected from the cathode with great velocity, striking the sides of the glass tube. The composition of the glass seemed to enter into this phosphorescence also, for while lead glass produced blue phosphorescence, soda glass produced a yellowish green.
The best scientific authorities now use the word "Cathode" in place of "Negative," the word Cathode coming from the Greek root meaning "descent; the path of generation, etc," From the Cathode pole emerge the swarm of electrons or corpuscles; from the same pole emerge those wonderful "rays" which have revolutionized scientific conceptions during the past decade.
Streams of these ``ions'' pour from many flames and from molten metals; and the impact of the cathode and ultra-violet rays causes them to gush even from cold bodies. In the vast laboratory of the sun it is but reasonable to suppose that similar processes are taking place. ``As a very hot metal emits these corpuscles, says Prof.
Through the lead-glass bowl I could see the X-ray tube inside suffused with its peculiar, yellowish-green light, divided into two hemispheres of different shades. That, I knew, was the cathode ray, not the X-ray, for the X-ray itself, which streams outside the tube, is invisible to the human eye. The doctor placed in our hands a couple of fluoroscopes, an apparatus by which X-rays can be detected.
The stream of new discoveries which followed Crookes's work justified his conviction that in cathode ray phenomena we have to do with a frontier region of physical nature. Still, the land that lies on the other side of this frontier is not the one Crookes had been looking for throughout his life.
This glow excites brilliant phosphorescence in glass and many substances, and these "cathode rays," as they are called, were observed and studied by Hertz; and more deeply by his assistant, Professor Lenard, Lenard having, in 1894, reported that the cathode rays would penetrate thin films of aluminium, wood, and other substances and produce photographic results beyond.
Craig was as calm as if his every-day work was experimenting on cadavers. He applied the current, moving the anode and the cathode slowly. I had often seen the experiments on the nerves of a frog that had been freshly killed, how the electric current will make the muscles twitch, as discovered long ago by Galvani. But I was not prepared to see it on a human being.
Where they strike on the glass of the tube it is seen to glow with a green or bluish phosphorescence, and it will ultimately soften with heat. These are the famous "cathode rays" of which we have recently heard so much.
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