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XXVII. On the Radioactive Matter in the Earth and flu- 

 Atmosphere. By A. S. Eve, M.A., Me Gill University, 

 Montreal*. 



IVTUMEROUS observers have found that part of the 

 -L^ ionization occurring within closed vessels is due to 

 penetrating radiation. These rays are attributed to the 

 presence of radium in the earth and of radium emanation in 

 the atmosphere. Experiments are described in this paper 

 which lead to an estimate of some of the magnitudes of the 

 quantities involved. 



Let K denote the number of ions, due to the 7 rays only, 

 generated per cubic centimetre per second at a distance of 

 one centimetre from one gram of pure radium bromide, 

 supposed concentrated at a point, and so placed that all the 

 rays are absorbed in air. Then Q grams at a point will 

 generate at a distance r, by the 7 rays alone, a number of ions 

 per c.c. per second denoted by N and given by, 



N=K-^" A ", (1) 



where \ is the coefficient of absorption of the 7 rays by air. 



The value of K has been approximately determined by 

 finding the number of ions produced per c.c. per second in 

 closed vessels made of various metals. These vessels were 

 placed at a distance of 303 cms. from 14*3 mg. of radium 

 bromide sealed in test-tubes, and placed behind lead 7 mm. 

 thick. The radium bromide used was that which Professor 

 Rutherford found gave per gram a heating effect of 110 

 gram-calories per hour. The experiments were made in the 

 Chemistry Building, where radium emanation has not been 

 artificially introduced. Vessels were made of clean com- 

 mercial sheets of lead, copper, zinc, iron, aluminium, and 

 tinned iron. These vessels were 51 cms. hio-h. and 23 cms. 

 in diameter (rig. 1). Two tubes were soldered into the sides, 

 so that dry filtered air could be drawn into the vessels when 

 required. Above each vessel was a small electroscope, 8 cms. 

 high and 6*5 cms. in diameter, made of clean tinned iron. 

 A rod within the electroscope carried a Dutch-metal leaf 

 observed by a microscope with a graduated eyepiece. This 

 rod was supported by sulphur, originally poured when in a 

 molten state into a larger cylinder of ebonite. This arrange- 

 ment gives excellent insulation and firm support. The rod 

 terminated within the lower vessel in a hook to which a rod 



* Communicated bv Professor E. Rutherford, F.R.S. 



