Radiation from Ordinary Materials. 531 



a glance how entirely different these curves are from those 

 for the other metals investigated. I have no explanation for 

 this difference, but it is well known that iron and steel are 

 anomalous in many other properties. The steel wires after 

 ha vino- been stretched are magnetized, and this suo'ofests that 

 a molecular change may take place in the steel, perhaps at a 

 definite point in the stretching, causing the steel at that 

 point to become harder. 



Up to the present no other substances have been in- 

 vestigated, but it is my intention to investigate the behaviour 

 o£ quartz fibres in the same way. They have been shown to 

 be very perfectly elastic for small distortions, but it is quite 

 possible that a slow creep does take place and could be 

 detected if much larger distortions were used. 



My best thanks are due to Prof. Poynting for his many 

 valuable and kindlv suggestions throughout the research. 



Birmingham Universitv, 

 Oct. 1904. 



L. The Radiation from Ordinary Materials. By Norman 

 R. Campbell, B.A., Fellow of Trinity College, Cambridge*. 



[Plate VII.] 



§ 1. ri^HE experiments of Patterson, McLennan, Strntt, 

 _L Righi, and others, have proved beyond doubt that 

 part of the "spontaneous" ionization in a closed vessel con- 

 taining gas is due to the influence of the walls. It is of the 

 utmost importance to determine the nature of this influence 

 — to ascertain whether it consists of Becquerel rays, and, if 

 so, to discover the nature of those rays. 



In this paper f two methods are described which have been 

 used for the solution of the problem, the later being suggested 

 by the earlier work. 



§ 2. All the experiments consisted in the measurement of 

 the spontaneous saturation current — or "leak," as it will be 

 called hereafter — through vessels of various forms and 

 materials. A preliminary description of the apparatus used 

 for the measurement is desirable. 



A Wilson gold-leaf electroscope J was employed and found 

 most satisfactory. The potential to which the insulated 

 system had attained in a given time was ascertained by means 



* Communicated by Prof. J. J. Thomson. 



t This paper contain- an account of the experiments, the results of 

 which were briefly indicated in a Letter to the Editor of 4 Nature ' 

 (vol. lxix. }». oil i. 



t C. T. R. Wilson, Proc. Camb. Phil. Sjoc. vol. xii. p. 135 (1903). 



