/i\i(h'inn /t\i</i(((i(>fi and Contdcl IJccI rir/'f //. 701 



' 



Atomic Weight. 



Difference of 

 Oscillatiou-Freciueiicies. 



1 



' M^ 



Ca 



24-36 

 40-1 



87-6 

 137-4 



91-7 

 223 



801 

 1691 



4858 



; Si' 



1 Ba 



Ka 





Dr. Watts' law makes the atomic weight o£ radium equal 



to 



177 if calculated from Mg, 

 IS7 „ „ 0., 



210 „ ,, Sr, 



233 „ „ Ba. 



The law found by Precht and the writer, that the differences 

 o£ the oscillation-frequencies of homologous doublets are 

 proportional to some power of the atomic w^eight, in other 

 words that the logarithm of the difference is a linear function 

 of the logarithm of the atomic weight, seems to furnish a 

 better means to calculate the atomic weight of radium from 

 its spectrum. It makes the atomic weight of radium 258. 

 Whether this value or the one found by Madame Curie, 225, 

 be the right one, is as yet open to discussion. 



Hannover Technische Hochscliule, C RUjSTGE. 



October 1903. 



LXXXVIIT. Radium Rad'/ation and Contact Electricity. By 

 Lord Blytilswuod, LL.l)., and H. S. Allen, M.A.^ B.Sc."^ 



WHEN the air between two insulated plates, of different 

 metals, is subject to the influence of a radioactive 

 substiince, similar wires connected with the plates acquire a 

 difference of potential. This difference may be measured 

 by joining the plates to the quadrants of a sensitive electro- 

 meter. It is of the same order of magnitude as that which 

 would be obtained by connecting the metal plates with a drop 

 of water. 



This effect was first observed in air under the radioactive 

 influence of a disk of the metal uranium by Lord Kelvin, 



* Communicated by Lord Kelvin. 

 Phil. May. S. G. Vol. G. No. 36. Dec. 190; 



3 A 



