﻿Ranges of the a. Particles from Uranium. 439 



From these surfaces the reflexion at the polarizing angle 

 sensibly disappears. The image of the paraffin flame could 

 be quenched by the operation of the polarizing nicol alone. 

 When the quarter wave-plate and analysing nicol were 

 introduced, a' and a could not be distinguished, the difference 

 probably not exceeding '05°, i. e. 3 minutes of angle. 



In order to examine the reflexion when the quartz was in 

 contact with a liquid of equal index, I had to mix alcohol with 

 the benzole. The behaviour was then much the same as with 

 glass of which the surface had been renewed by hydrofluoric 

 acid. No precise measures could be taken, but the reflexion 

 at 45° incidence seemed less than from the glass, though 

 still easily visible. It spite of repeated trials with inter- 

 mediate cleanings, it was difficult to feel sure that the 

 residual effect might not be due to foreign matter, the more 

 as differences could sometimes be detected between various 

 parts of the surface *. Even if the surface could be 

 regarded as clean on immersion, there is no certainty that 

 a capillary film of some sort might not be deposited upon it 

 from the liquid. The cause of the small residual reflexion 

 must remain for the present an open question. 



XL. The Ranges of the ol Particles from Uranium. By 

 H. Geiger, Ph.D., Lecturer in Physics, and J. M. Nuttall, 

 JB.Sc, Graduate Scholar, University of Manchester f. 



IN connexion with a re-determination of the ranges of the 

 a particles of a number of radioactive products, we have 

 pointed out in a previous paper % that there exists a quanti- 

 tative relation between the range of an a particle and the 

 transformation constant of the product from which it arises. 

 This was arrived at by plotting the logarithms of the trans- 

 formation constants against the logarithms of the ranges of 

 the respective products. In this way approximately straight 

 lines were obtained passing through the points representing 

 the products of the Uranium-Radium and of the Actinium 

 series. No details have yet been given for the Thorium 

 series on account of insufficient data. 



A certain difficulty remained as regards uranium. As Bolt- 

 wood § has shown, this substance emits two a particles tor one 



* At the top of the plate, where it was attached to a handle, a slight 

 invasion of gelatine (used as a cement) gave rise to a copious reflexion : 

 but this film was easily visible in the air. 



t Communicated by Prof. E. Rutherford, F.R.S. 



% II. Geiger and J. M. Nuttall, Phil. Mag. vol. xxii. p. 613 (101 IV 



§ J>. B. ISoltwood. Amer. Journ. of Sci. vol. xxv. p. 269 (IOCS). 



