852 Dr. B. W. Boyle on the 



strongly than toluol ; higher members of the benzene series, 

 for instance, might be examples. 



Determinations of the coefficient were also made with 

 mercury and with sea-water. It was desired to find if the 

 former absorbed, or occluded, the emanation to any appre- 

 ciable extent, and measurements on the latter had a bearing 

 on the values of natural ionization found over the ocean 

 and the disparity between these values and those over the 

 land. 



The observations with mercury showed that it does not 

 absorb the emanation to an appreciable extent, and that in 

 the experiment any emanation which was mechanically 

 suspended in the mercury was not enough to be detected 

 within the error of experiment. AYlien the 7-ray measure- 

 ments were made care was taken not to disturb the mercury 

 in the bulb from the position it had when the bulb was laid 

 aside to wait for radioactive equilibrium. This prevented 

 the occlusion of some of the Ka C in the mercury, and 

 the consequent appreciable absorption of 7 rays bv the 

 latter. 



The sample of sea-water experimented on was taken from 

 a river estuary in Wales ; its specific gravity at 14° 0. was 

 1'022. The value obtained for the coefficient (one deter- 

 mination) was 0*255. This is a very appreciable absorption, 

 and its value must have a bearing on the results obtained 

 for the natural ionization and amount of radioactive products 

 in the atmosphere, over the ocean and over the land. Both 

 these quantities vary between very wide limits : but it is 

 certain that, on an average, they are less over the ocean than 

 over the land. The facts have been well brought out in a 

 recent paper by Simpson and Wright*, who showed in 

 addition that generally the natural ionization and the amount 

 of radioactive products increased as land is approached from 

 mid-ocean. The natural ionization is to some extent dependent 

 on the quantity of radioactive products, and this latter to 

 some extent on the amount of radium emanation present. 

 On account of the absorbing power of the ocean there should 

 be less emanation per unit volume of air over the ocean than 

 over the land, whence the greater part of the emanation is 

 supplied ; and for the same reason this quantity of emanation 

 should increase as land is approached from mid-ocean. Pro- 

 bably this is not the only explanation for the disparity 

 mentioned, but certainly it is a contributing effect. 



* Proe. Roy. Soc. A. lxxxv. p. 175 (1911). 



