On the day when history entered the new century, Lord Kelvin, a famous elder in British science, delivered a famous speech at the Royal Society on April 27th, 1900.

Lord Kelvin, whose real name is william thomson, is an outstanding theoretical and experimental physicist in Britain. At the age of 22, he became a professor of natural philosophy at Glasgow University. He has made remarkable achievements in electromagnetism and thermal research, and published about 700 scientific papers in his life. Starting from 1858, he led the completion of the submarine cable laying project across the Atlantic and connecting Europe and America. He also established the first physics laboratory for Dabei. Because of his outstanding achievements and contributions, he was elected as a member of the Royal Society of London in 185 1, served as the president of the Royal Society from 1890 to 1895, and was made Lord Kelvin in 1892.

Lord Kelfen later wrote an article based on this speech at the beginning of the new century, which supplemented the work from the beginning of 1900 to the completion date of the article (1901February 3) 13 months, and expanded the problems expounded in the speech. His secretary, Anderson, helped him draw all kinds of accurate geometric figures, performed many algebraic and arithmetic operations, and checked a large number of individual results. Kelfen's article entitled "Dark Clouds in the 9th Century Suspended over Thermodynamic and Photodynamic Theories" was published in the joint issue of Journal of Philosophy and Journal of Science in July, 190 1.

At the beginning of the article, Kelfen wrote bluntly: "Dynamics theory asserts that heat and light are both modes of motion, but now, the beauty and clarity of this theory are covered by two dark clouds. With the wave theory of light studied by Fresnel and Thomas Yan, the first dark clouds began to appear. Including the question: how does the earth move through an elastic solid, which is essentially a light ether? The second dark cloud is Maxwell Boltzmann's theory of energy sharing. "

Regarding the first dark cloud, that is, "the relative motion between ether and measurable objects", Kelfen reviewed and analyzed physicists' views on this issue. He believes that if we have a satisfactory basic relationship between ether and matter, instead of the old embarrassing concept that when the atoms of matter move relative to the ether around them, the atoms will repel the ether in the space in front of them, then all phenomena can be fully explained more quickly.

Kelvin agrees with Fresnel very much. He disagreed with Thomas Yan that the ether was not completely free when it passed between molecules and atoms, just like a breeze blowing through trees.

According to Fresnel's static ether theory, if we ignore the rotation of the earth and the movement of the whole solar system, there should be an ether flow of 30 kilometers per second on the tangent parallel to the earth's orbit. "But, alas! Something contradictory to this conclusion happened, and the ether in the earth's atmosphere did not move relative to the earth. " Michelson and Morey's experiments proved this point. "I can guarantee that the results of the experiment are reliable" and "I don't see any defects in the idea or implementation of the experiment".

However, the "brilliant proposal" independently put forward by Fitzgerald and Lorenz seems to be out of the predicament, which makes it possible that "the experimental results cannot refute the conclusion that the ether moves freely in the space occupied by the earth". Although Kelvin prefers the static ether theory and agrees with the contraction hypothesis, he still seems to think rationally that this problem remains unsolved. He is cautious about this here: "We must also look at the first dark cloud very densely."

Kelvin spent most of his time discussing the "second dark cloud" in detail. He briefly reviewed the process of energy balance theory, analyzed the content of the theory and the difficulties encountered, and especially listed the distance between the theoretical calculation value and the actual observation value of the specific heat of diatomic or polyatomic gases. Kelfen asserts: "The obvious deviation observed is absolutely enough to prove Boltzmann-Maxwell theory", "In fact, the deviation of Boltzmann-Maxwell theory is greater than what we have listed" and "there is no possibility that Boltzmann-Maxwell theory is consistent with the real situation of gas specific heat."

In his article, he strongly emphasized two bold conclusions: as far as Boltzmann-Maxwell theory is concerned, he is quite dissatisfied with the unproven mathematical conclusion and the unreliable experimental conclusion. Contrary to Rayleigh's attempt to defend Boltzmann-Maxwell theory, Kelfen clearly pointed out: "The simplest way to achieve the expected result is to deny this conclusion."

He confidently predicted that the second flower "covered the dark clouds of heat and light molecules in the last quarter of the nineteenth century, and people could make it disappear at the beginning of the twentieth century."

In the history of physics, Lord Kelvin is famous for his conservatism, but his speech is profound and to the point. He not only gained insight into two difficult problems in physics in the19th century, but also pointed out a more sensible direction of efforts. This is of course related to his intuitive ability of genius, and I am afraid we can't ignore the influence of the torrent of physics revolution at the turn of the century.