Part 9

If an electron falls from the M-ring on to the L{1}-ring, it will radiate an amount of energy slightly different from that radiated by an electron falling from the M-ring on to the L_{2}-ring. The wave-lengths corresponding to these radiations will therefore be slightly different and the corresponding lines in the spectrum, indicating these wave-lengths, will therefore consist of a pair of lines close together—a doublet. Now let us consider what happens when the electrons fall from the N-ring. The electron which falls from the N-ring, whether it falls on the L_{1}- or the L_{2}-ring, will radiate more energy than the electron from the M-ring. But the difference in the energy radiated, depending on whether it falls on to the L_{1}- or the L_{2}-ring, is obviously the same as the corresponding difference in the case of an electron falling from the M-ring. It is the difference in the two paths which is concerned, and this difference is simply the distance between the L_{1}- and the L_{2}-rings. In the case of electrons falling from the N-ring, therefore, although the actual amounts of energy radiated are greater, and therefore the corresponding wavelengths are shorter, yet the resulting pair of lines are at the same distance apart as in the case of the M-ring. Similar reasoning applies to any pair of electrons which start from the same outer ring and fall, one on the L_{1}-ring, and the other on the L__{2}-ring. In each case, a doublet is produced, and all these doublets have their component lines separated by the same interval.

This theory gives a satisfactory explanation of the observed equality of the L-doublets, but we can go on to deduce a result from it which can be used as a test. We have seen that the K α-line in the K-spectrum is produced by the passage of an electron from the L-ring to the K-ring. But there are two L-rings. The passage of an electron from each of these to the K-ring should produce a line in the K-spectrum. These two lines should be very close together; they should form a doublet. Now we have seen that the K α-line actually is a doublet. But we can go further. The difference in path, according to whether the electron falls on the K-ring from the L{1}- or the L_{2}-ring, is the same as the difference in the paths of two electrons, coming from the same outer ring, but falling one on the L_{1}-ring and the other on the L_{2}-ring. So that the interval between the components of the K-doublet should be the same as the interval between the components of the L_-doublets. This result is confirmed by actual measurement. The “interval” or “distance” between the components of a doublet is really a difference, of course, in the hardness of the corresponding waves.

We have said sufficient to make the main lines of the theory clear. We need only add that the further explanation of the L-spectrum and also of the M-spectrum requires us to assume that the M-ring also is not a single ring, but consists of two or more.

INDEX

A α-RAYS, 65 Aluminium, 154 Anti-cathode, 73 Argon, 141 Atom, 33 Atomic numbers, 82 Avogadro, 34

B ß-rays, 65 Balmer, 127 Barkla, 168 Black body, 114 Bohr, 123 Bragg, 118 Brownian movement, 45

C Cathode rays, 55 Compounds, formation of, 29 Crystal analysis, 166

D Dalton, 23 Debye, 122 Diffusion, 40

E Einstein, 46, 105, 120 Electron, mass of, 60 —— radius of, 62 Element, 28

F Fraunhofer, 123

G γ-rays, 65, 74 Gases, Kinetic Theory of, 42 Geological strata, age of, 70 Gold atom, 88 Gramme-atom, 37

H Helium atom, 86, 147 —— nucleus, 87, 108 Hertz, 54 Hydrogen atom, 85

I Inert gases, 142 Ions, 56 —— charge on, 58 Isotopes, 102

K Kirchhoff, 114, 123

L Laue, 166 Light, velocity of, 54 Lithium atom, 90, 149

M Magnetic properties of the elements, 157 Maxwell, 42, 53 Mendeléev, 77 Molecule, 33 Monochromatic light, 125 Moseley, 170

N Neon, 144 Newlands, 77 Nitrogen, 152

P Periodic system, 77 Perrin, 46 Planck, 119, 127 Prout, 25

R Radium, 63 —— disintegration of, 95 Relativity and the atom, 104, 133 Rutherford, 93

S Sommerfeld, 122, 134 Stokes, 57

T Temperature, absolute zero of, 42

U Uranium, 79

W Waves, longitudinal and transverse, 124, 165

X X-rays, 70, 167, 168