Vacuum Tubes and Radiant Matter
We had seen on another thread that Hauksbee (enabled by Boyle) was able to generate electricity inside vacuum back in 1705. Over a hundred and fifty years later—armed with more advanced and reliable glass forming techniques, as well as better pump systems—William Crookes was one of dozens of scientists that helped develop the technology of vacuum tubes. These tubes, when linked to an electric circuit, produced a similar glow to that seen by Hauksbee in his sphere. But there was so much more that Hauksbee missed! In a wonderfully written paper titled On Radiant Matter (1879) Crookes begins by acknowledging that he stole the title from Faraday, and pays homage to “the great philosopher”, by saying he was the first to classify matter into four states—solid, liquid, gaseous, and ‘radiant’ (plasma). Crookes then proceeds to describe the effects of vacuum on the mean-free path of gas molecules and how this gas becomes radiant when enough voltage is applied. Through wonderful narrations and drawings that he describes to the reader as if they were pictures, he points out the various colors that are possible depending on the type of glass used (e.g. country of origin or ore extract). At the same time, he notices that other “phosphorescent” metal ores can be placed in the glass to generate a similar effect, expanding the color palette even further. Other curiosities are mentioned, among them that poor vacuum creates streaks which go directly to the positive electrode while high vacuum makes the bulb glow uniformly and independent of the position of the positive electrode (the first compact fluorescent lightbulb?). Furthermore, he points out that objects can cast shadows from these emissions, and therefore must travel in a straight line. But the most important advancements happen in Part II of the paper, where he shows that the emissions can push objects and that they can be deflected by magnetic fields. He proceeds to make a sort of motor, where the beam is concentrated using a magnet and makes the positive electrode (shaped as a waterwheel) spin. In his final section, he reflects on all his learnings and considers the size of molecules and atoms—and he feels humble amongst all those zeros in his calculations. Crookes realizes that the numbers he is dealing with are astoundingly big! He asks the reader: how long would it take for one of his evacuated bulbs to reach atmospheric equilibrium if he were to leak in a hundred million air molecules per second. “An hour? A day ? A year? A century? Nay, almost an eternity!—a time so enormous that imagination itself can not grasp the reality”. Finally, after blowing our minds with discovery, invention, and facts, he closes his paper with a passage from Edmund Spenser’s epic poem The Faerie Queene:
“Yet all these were, when no man did them know,
Yet have from wisest ages hidden beene;
And later times things more unknowne shall show.
Why then should witlesse man so much misweene,
That nothing is, but that which he hath scene"
It is a wonderful paper, and although Crookes never explicitly said it, the fact that he noticed that these beams were charged particles with finite mass, marks (imo) the birth of particle physics. The Faerie Queene Pandora's atomic box was opened.
Source: Crookes, W. On Radiant Matter I. Popular Science Monthly 16, 13–24 (1879).
License CC BY 4.0
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Full disclosure, I may occasionally borrow a sentence from Will Durant's Story of Civilization. I absolutely love that collection!