566 C. Barus — Coronas of tht Fog Layer. 



cubic centimeter), and the too- particles from a diameter of 

 about 2xl0-' cm to 10-' cm . 



In do case was there any dislocation of coronas, or of color, 

 detected, though naturally the coronas in case of reflection from 

 the mirrors were somewhat more yellowish in color (due to the 

 reflecting surfaces) and less vivid (due to the reflections and 

 greater thickness of fog layer) ; for it is hardly probable that 

 the fog particles are quite of a size. The continuity of corre- 

 sponding colored rings, however, was exact within the limits of 

 observation. Hence thicknesses of 15 on] and over 15™' produce 

 identical coronas identical in aperture ; or the thickness of the 

 cloud kyer is without influence on the coronas. 

 Brown University, Providence, E. I. 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. The Radium Contents of some Uranium Minerals. — It lias 

 been shown by Boltwood and also by Strntt that in inauy miner- 

 als a constant relation exists between the amounts of uranium and 

 radium present, as would be expected from the theory of the 

 formation of radium through the intermediate uranium-X and 

 ionium. Recently Mile. Gleditsch has found these relations to 

 vary considerably (in the ratio 100 : 86 : 68) in thorianite, Joachims- 

 thal pitchblende, and autunite. Soddy and Pirret, while finding 

 a constant ratio in thorianite and the pitchblende, have also found 

 a deficiency of radium in autunite. aIarckwald and Russell 

 have now confirmed the last mentioned result, and have made a 

 further study of the autunite, which is a calcium-uranium phos- 

 phate with the formula Ca(UO a ),(POJ,.8H„0. This mineral, 

 besides containing less than the expected amount of radium, is 

 remarkable in containing no appreciable amount of lead as well 

 as less helium than the required amount. From the amount of 

 helium present, Soddy has calculated that the age of the mineral 

 would be only about 30 years if none of this gas had been lost, 

 whereas the radium corresponded to an age of many thousand 

 years, so that he assumed that the radium in the mineral came 

 from without and crystallized as an isomorphous replacement of 

 calcium, instead of being a product of the uranium. This view 

 of Soddy's appeared improbable to Marckwald and Russell, so 

 that they investigated the ionium contents of the mineral and 

 found its amount to be only slightly less than normal in propor- 

 tion to the uranium. Since ionium has an average life of not less 

 than 30,000 years, it follows that the age of the autunite must be 



