72 Scientific Intelligence. 



arranged in shells, the outer boundary of the magnetic field coin- 

 ciding with a place where the electric force vanishes." 



AYlien more than one electron forms a part of the normal 

 atom, the position of equilibrium will not be where the force due 

 to the positive nucleus vanishes, but where this force at any 

 electron balances the repulsion due to the other electrons. 

 Therefore the earlier condition cu — n-n changes to cu = tt 

 (71 + 8), where 8 is a quantity depending on the repulsion of 

 the electrons and perhaps also on n. The frequency formula 

 now assumes the Rydberg form l/(m + S') 2 + l/(n + S) 2 . In 

 the discussion of this expression, Thomson shows that the pro- 

 cesses of ionization and a supposed shrinking toward the center 

 of the outer boundary of the magnetic field account for the exist- 

 ence of a principal series, of the first and second subordinate 

 series, and of the well-known mutual connections between these 

 series such as the Rydberg-Schuster law, common convergence 

 frequencies, etc. Doublets and triplets arise from asymmetry, 

 with respect to the nucleus, in the distribution of electrons 

 belonging to the same ring, since this asymmetry would cause r 

 to have slightly different values for the various electrons and 

 hence give rise to different frequencies of vibration. 



In addition to the topics barely suggested above, the paper 

 contains a wealth of other valuable material for the details of 

 which the reader may be referred to the original text. Two 

 remaining points, however, deserve special notice. By assuming 

 a certain simple relation between the electric and magnetic 

 forces, Thomson deduces Planck's law. He also calculates the 

 number of waves in a train, after proving that the time taken 

 for the energy lost by radiation to fall to 1/e of its initial value 

 is equal to 10 22 /5?i 2 . This leads to 4 X 10 6 waves for the D lines 

 of sodium, and to 660 waves for the characteristic X-rays of the 

 L series of platinum. — Phil. Mag., 37, 419, 1919. h. s. u. 



4. Absorption of X-Rays. — The relative absorption coeffi- 

 cients of X-rays, for a comparatively large number of different 

 elements, have been very thoroughly investigated by T. E. 

 Auren. The success of the work was largely due to the appli- 

 cation of a compensation method, for which the apparatus was 

 admirably designed, and to the care taken to minimize and cor- 

 rect for small sources of error. The chief results obtained may 

 be summarized as follows : 



(1) In the chemical compounds examined the additive law 

 has been found to hold unqualifiedly. With the possible 

 exception of carbon, the state of aggregation seemed to 

 ■ have no influence on the quantity of absorption. The 

 valency of the same element as a constituent of different 

 compounds had no detectable effect on the magnitude of 

 the absorption of the element in question. 



