Historical Figure
J. J. Thomson
1856–1940
British physicist (1856–1940)
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Biography
Sir Joseph John Thomson was a British physicist. He received the 1906 Nobel Prize in Physics "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases." In 1897, he showed that cathode rays were composed of previously unknown negatively charged particles, which he calculated must have bodies much smaller than atoms and a very large charge-to-mass ratio. The electron was the first subatomic particle to be discovered.
In Their Own Words (5)
The electron: may it never be of any use to anybody!
A popular toast or slogan at J. J. Thomson's Cavendish Laboratory in the first years of the 1900s, as quoted in Proceedings of the Royal Institution of Great Britain, Volume 35 (1951), p. 251. , 1951
As the cathode rays carry a charge of negative electricity, are deflected by an electrostatic force as if they were negatively electrified, and are acted on by a magnetic force in just the way in which this force would act on a negatively electrified body moving along the path of these rays, I can see no escape from the conclusion that they are charges of negative electricity carried by particles of matter.
"Cathode rays" Philosophical Magazine, 44, 293 (1897). , 1897
We see from Lenard's table that a cathode ray can travel through air at atmospheric pressure a distance of about half a centimetre before the brightness of the phosphorescence falls to about half its original value. Now the mean free path of the molecules of air at this pressure is about 10-5 cm., and if a molecule of air were projected it would lose half its momentum in a space comparable with the mean free path. Even if we suppose that it is not the same molecule that is carried, the effect of the obliquity of the collisions would reduce the momentum to half in a short multiple of that path. Thus, from Lenard's experiments on the absorption of the rays outside the tube, it follows on the hypothesis that the cathode rays are charged particles moving with high velocities, that the size of the carriers must be small compared with the dimensions of ordinary atoms or molecules. The assumption of a state of matter more finely subdivided than the atom of an element is a somewhat startling one; but a hypothesis that would involve somewhat similar consequences—viz. that the so-called elements are compounds of some primordial element—has been put forward from time to time by various chemists.
Royal Institution Lecture (April 30, 1897) as quoted by Edmund Taylor Whittaker, A History of the Theories of Aether and Electricity from the Age of Descartes to the Close of the Nineteenth Century (1910). , 1910
This example illustrates the differences in the effects which may be produced by research in pure or applied science. A research on the lines of applied science would doubtless have led to improvement and development of the older methods—the research in pure science has given us an entirely new and much more powerful method. In fact, research in applied science leads to reforms, research in pure science leads to revolutions, and revolutions, whether political or industrial, are exceedingly profitable things if you are on the winning side.
Cited from Lord Rayleigh, The Life of Sir J. J. Thomson (1943), p. 199. , 1943
If, in the very intense electric field in the neighbourhood of the cathode, the molecules of the gas are dissociated and are split up, not into the ordinary chemical atoms, but into these primordial atoms, which we shall for brevity call corpuscles; and if these corpuscles are charged with electricity and projected from the cathode by the electric field, they would behave exactly like the cathode rays.
"Cathode rays" Philosophical Magazine, 44, 293 (1897). , 1897
Timeline
The story of J. J. Thomson, told in moments.
Appointed Cavendish Professor of Physics at Cambridge. He was 27. Many older physicists were offended. One reportedly said, "Things have come to a pretty pass when they elect mere boys."
Announced his discovery of the electron at the Royal Institution. He showed that cathode rays were particles over 1,800 times smaller than a hydrogen atom. He called them "corpuscles." The name didn't stick.
Proposed the "plum pudding" model of the atom. Electrons embedded in a sphere of positive charge, like plums in a pudding. His own student, Rutherford, proved him wrong.
Won the Nobel Prize in Physics for his work on electrical conduction in gases. Seven of his research assistants also won Nobel Prizes. His son George won one too, for proving electrons were waves.
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