Prof. Thomson, On the presence of Radio- Active Matter, etc. 391 



On the presence of Radio- Active Matter in ordinary substances. 

 By J. J. Thomson, M.A., F.R.S., Cavendish Professor of Experi- 

 mental Physics. 



[Read 15 February 1904.] 



In a paper read before the Society in May, 1903, I showed 

 that there is in the water supplied by the Cambridge Water 

 Works, and also in the water from many of the wells in the 

 neighbourhood a radio-active gas, and by the kindness of Professor 

 Dewar I was able to show that this gas could be liquefied. Since 

 the date of that paper I have examined specimens of water from 

 wells in various parts of the country; for these specimens I am 

 indebted to the kindness of Professor Bedson, Middlesborough ; 

 C. Joyner, Esq., Icknield Square, Birmingham ; The Buddow 

 Brewery Co., Chelmsford ; Messrs Salt and Co., Burton-on-Trent ; 

 Messrs Worthington, Burton-on-Trent; The Preston Colliery Co., 

 North Shields ; A. P. Jenkin, Esq., Redruth ; A. Bosville, Esq., 

 Bridlington ; E. J. Russell, Esq., Wye, Kent ; E. Hinks, Esq., Croy- 

 don ; F. Everett, Esq., Dover. Eighteen specimens were examined 

 and in 15 of these considerable quantities of the radio-active gas 

 were found ; the amount of this gas varied considerably in the 

 different specimens, in two cases it greatly exceeded the amount 

 in the Cambridge water. Measurement of the rate of decay of 

 the radio-activity of the gas expelled from these waters, as well 

 as that of the induced radio-activity due to it, showed that the 

 gas was identical with that contained in the Cambridge water, 

 which again is identical with the emanation from radium. The 

 same gas has recently been found by Professor Bumpstead in the 

 water at Newhaven, Connecticut, U.S.A. There is thus reason 

 for believing that this gas is a constituent of most waters which 

 have not been allowed to stand out of contact with the soil for 

 too long. For as the radio-activity of the gas dies away to half 

 its value in about four days and diminishes in geometrical pro- 

 gression with the time, it naturally ceases to be appreciable in 

 water which has stood out of contact with the ground through 

 which it has percolated for more than a fortnight or so. As 

 the gas is identical with the emanation from radium it seemed 

 desirable to see whether traces of radium could be found in the 

 soil through which the water had percolated. Elster and Geitel 

 had already shown that a radio-active gas is given off hy the soil. 

 I have therefore made a series of experiments, which have shown 

 that a radio-active substance, apparently radium, is exceedingly 

 widely distributed, occurring in the most unexpected places. 



