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Resonance Radiation of Sodium Vapor.
(R. W. Wood and Fred Mohler, “Resonance Radiation of Sodium Vapor excited by one of the D-lines.”)
(Physical Review, XI, p. 70 (II), 1918.)
In 1905 Wood showed that if a sodium flame containing vapors of pure sodium is illuminated, the latter begin to emit yellow light. Wood called this radiation resonance radiation. In its spectral composition the resonance radiation proved to be identical with the exciting radiation, i.e. its spectrum consisted of two lines—$D_1$ and $D_2$. The question arises: what will the picture be if sodium vapor is illuminated by only one spectral line, $D_1$ or $D_2$; will the resonance spectrum likewise consist of one line, or of two? The answer to this question makes it possible to look more deeply into the very mechanism of radiation. Namely, it makes it possible to decide whether the centers producing the lines $D_1$ and $D_2$ are connected with one another, or whether they are independent of one another.
The paper under review is the second attempt in this direction. The first attempt1 did not yield definite results. To separate the $D$ lines the authors used a special polarization method, described earlier by Wood2. Most of the experiments were carried out with the $D_2$ line, since it is approximately twice as bright as the $D_1$ line. The result proved to be that the resonance spectrum consists of both lines, $D_1$ and $D_2$, under two conditions: 1) when traces of hydrogen are present in the bulb containing the sodium vapor, and 2) at sufficiently high temperatures (270–350°). The authors maintain that precisely under these conditions it becomes possible for energy to be transferred from the centers giving the line $D_2$ to the centers giving $D_1$, this transfer, in their opinion, taking place by way of molecular collisions. An analogous transfer of energy is observed in resonance in iodine vapors. When helium is mixed with vapors of pure iodine, the very character of the spectrum changes: the spectrum consisting of a system of doublets grows pale, and a continuous spectrum, barely noticeable before, appears brightly. Here there occurs a transfer of energy from the systems giving doublets to the systems giving the continuous spectrum.
E. Shpolsky.
On the Question of the Greatest Frequency of X-Rays and Gamma Rays.
(E. Rutherford. “Penetrating Power of the X Radiation from a Coolidge Tube.” Phil. Mag. (6), 34, p. 153, 1917.)
The paper is a continuation of an investigation carried out by the author together with Barnes and Richardson in 1915. In this original work Rutherford came to the conclusion that there exists a certain maximum frequency, and consequently also a hardness, which—