788 Mr. A. Stephenson on Displacements 



4*5 (mean of A and B). The percentage caught is therefore 



450 



-=*-, or 63 per cent. (See also II. p. 783.) This is at the 



ordinary laboratory temperatures. 



Further experiments with air streams of magnitudes *11, 

 *25, and *80 litre per minute showed that at these speeds the 

 amounts of emanation caught were 86, 73, and 23 per cent, 

 respectively. 



Summary. 



Experiments have been made on the absorption of radium 

 emanation by coconut charcoal, the emanation being carried 

 to the charcoal by a stream of air. It has been found 



(a) that with weak solutions the amount of emanation 



absorbed in short exposures of the same time for the 

 same strength of air-stream is proportional to the 

 strength of" the solution ; 



(b) that with the same solution and strength of air-stream 



the amount absorbed for exposures of different times 

 does not increase in proportion to the time of expo- 

 sure but falls off, showing that the charcoal is getting 

 saturated ; 



(c) that under the conditions of the experiments the 



amount of emanation absorbed does not depend on 

 the humidity of the air ; 



(d) that with tubes 8 sq. cm. in cross-section containing a 



column 30 cms. long of coarsely powdered coconut- 

 charcoal the amount of emanation absorbed when 

 the air-stream is "5 litre per minute and the exposure 

 is 21 hours, is only about 02 per cent, of the total 

 amount of emanation carried by the air to the tube. 



In conclusion the author wishes to express his best thanks 

 to Professor Sir J. J. Thomson for permission to carry out 

 the above research at the Cavendish Laboratory. 



Cambridge, June 17, 1930. 



LXXXV1I. On Displacements in the Spectrum due to 

 Pressure. By Andrew Stephenson *. 



IT has been suggested in connexion with the peculiar 

 resonance effects exhibited in the spectra of sodium and 

 other vapours, that a series of lines is, in certain cases, the 

 spectroscopic analysis of the individual oscillatory motion of 

 a single coordinate under the disturbing influence of some 



* Communicated by the Author. 



