Variation of Emanation Content of Certain Springs. 815 



general conclusions as to recoil phenomena can be deduced 

 from this fact since radium B and radium D are isotopic 

 elements, and must therefore be expected to behave alike. 

 Possibly in other cases of radioactive disintegration the recoil 

 streams may consist of particles with multiple charges; but 

 unfortunately there are no other cases which lend themselves 

 to easy experimental investigation. 



We are indebted to Sir Ernest Rutherford for putting 

 at our disposal the large quantities of radium emanation 

 without which successful experiments would have been 

 impossible. We have also to thank Mr. C. W. Gamble, of 

 the Manchester School of Technology, for helping us to make 

 the Schumann plates used in these experiments. 

 Physical Laboratories, 



The University, Manchester. 



LXXXVTI. The Variation of the Emanation Content of 

 Certain Springs. By R. R. Ramsey, Ph.D., Associate 

 Professor of Physics, Indiana University, Bloomington, 

 2nd., U.S.A.* 



WHILE measuring the radioactivity of springs in the 

 neighbourhood of Bloomington, Indiana, I found 

 that measurements made at one time did not agree with those 

 made at another time. The discrepancy was so great, that 

 I set out to determine if the difference was due to errors or 

 due to an actual change of the value. I selected two springs' 

 and have tested them once a week during the last nine 

 months. 



The method of measurement was the Schmidt shaking 

 method (Phys. Zeit. vol. vi. p. 5G1, 1905). This method 

 has been found to have an accuracy of about 5 per cent, 

 when measurements are made at the spring, and an accuracy 

 of about 3 per cent, when measurements are made in the 

 laboratory (Am. Journ. Sci. vol. xl. p. 311, 1915). 



An emanation electroscope was used. This electroscope 

 was at first calibrated by means of Duane and Laborde ; sf 

 empirical formula, which holds for an electroscope of 

 one litre capacity. Later, the electroscope was calibrated by 

 means of emanation standard E 5-1, which is certilied by the 

 Bureau of Standards to be accurate to within 3 per cent. 

 The two methods of calibration agreed within 5 per cent. 



* Communicated by the Author. 



f Le Radium, vol. xi. p. 5 (1914) ; Ann. der Phys. vol. xxxviii. p. 959 

 (1912) ; Compt. Rendus, vol. cl. p. 1421 (1910) ; Journ, de Phys. vol. iv. 

 p. 605 (1905) ; Indiana Acad. Proc. 1914. 



