﻿152 Prof. E. Kutherford : Distribution of the 



The letter ju, (strictly speaking denoting " molecular con- 

 ductivity") has been retained, for the sake of simplicity, to 

 represent also " atomic conductivity." The table has been 

 entirely constructed from the data in Laiidolt-Bornstein's 

 Physikalisch-Chemische Tabellen (latest, 1905, edition). In 

 all cases, the atomic conductivities given are the means of 

 those obtained by all the possible calculations. To calculate 

 the molecular conductivity of any salt, base, or acid, respect- 

 ively, the equation pv x + pv x , /w M + /*t? 0H , or B,v sx . f iv K + fiv„ 

 should be employed. 



East London Technical College, 

 London, E. 



XXII. Distribution of the Intensity of the Radiation from 

 Radioactive Sources. By E. Rutherford, F.R.S., Mac- 



donald Professor of Physics, McGill University, Montreal* . 



[Plate II.] 



IX the course of my experiments on the magnetic deflexion 

 of the a rays emitted by the active deposit of radium, a 

 very peculiar photographic effect was observed. The ex- 

 perimental arrangement was similar to that described in 

 a previous paper (Phil. Mag. July 1905). The rays from a 

 wire about 1*5 cms. long and 0*5 mm. in diameter, made 

 strongly active by exposure in the radium emanation, passed 

 through a slit and fell on a photographic plate placed some 

 distance above the slit. The whole apparatus was exhausted 

 of air, and a strong magnetic field applied so as to bend the 

 pencil of a rays. With a broad slit, comparable in width 

 to the diameter of the active wire, the photographic trace 

 of the a rays on the plate is shown by a black band with 

 sharply defined edges ; and the intensity of the photographic 

 impression is approximately uniform over its cross section. 

 With a very narrow slit, however, the photographic trace of 

 the rays has a very different appearance. 



Fig. 1 A, PI. II., shows a magnified drawing of such a trace. 

 The outside edges of the band are sharply defined, and the 

 photographic impression falls off rapidly from the outside to 

 the centre, but is most intense at the extreme edges. The 

 trace, at first sight, appears as if it consisted of two dark 



* Communicated by the Author, having been read before the American 

 Physical Society, April 1906. 



