534 THE ENGRAVED ROCK OF LOE. 



comparisons with Loe cannot be made. Possibly this is the 

 place referred to by C J. Andersson* as follows : — 



The natives of these parts have a strange tale of a rock, in which 

 the tracks of all the different animals indigenous to the country are 

 distinctly visible; moreover, that man and beast lived here together in 

 great amity, but one day, from some unknown cause, their Deity appeared 

 unexpectedly and dispersed them. I never had the good fortune to 

 obtain a sight of this marvellous rock. Mr. Moffat, who makes mention 

 of a similar story prevailing among the Bechuanas, was equally unsuc- 

 cessful. 



As to ithe meaning of Loe, speculation can scarcely hope to 

 be profitable while so little really is known either of the old 

 engravings of South Africa or of the artists who made them. 



In conclusion, the writer's thanks are due to Mr. Knobel 

 for his valued co-operation to Dr. Poch for the use of his 

 photographs, and to Mr. A. M. Cronin for so kindly photograph- 

 ing the rubbings made at Lo€. 



Radium Production. — According to Scieiice,-\ the 

 radium output of the Standard Chemical Company, of Pitts- 

 burgh, during the years 1913-1917 amounted to 25.4 grams of 

 the element, and during 19 18 the output was 13.6 grams, making 

 a total of 39 grams for the six years. It is estimated that the 

 total radium production in the United States to 1919 approxi- 

 mates 55 grams of the element, or probably more than halt of 

 all the radium produced in the world. 



Ageing of Chemical Elements. — It has recently 



been suggested that the remarkable difterence in the atomic 

 weight of what for purposes of distinction have been termed 

 " common " lead and " radioactive "' lead may be accounted for 

 by a process of " ageing." According to this hypothesis, what is 

 now " common " lead, at the time of the formation of the earth 

 .had an atomic weight of 206.08 and a density of 11.27, but that 

 as the aeons rolled by the speed of the electrons in the lead atom 

 slowed down, and so the atomic weight rose to 207.19 and the 

 density to 11.34. Hence " neo " lead. i.e.. lead freshly formed 

 by radioactive disintegration, would increase in mass, and in ages 

 to come will possess a higher density and atomic weight than it 

 does now. Reasoning along these lines, it is suggested that the 

 atomic weight of atmospheric or mineral helium must be .0214 

 higher than that of helium produced by radioactive disintegration, 

 so that while the atomic weight of " common " helium is 3.94, that 

 of " neo " helium must be 3.92. 



*"Lake N'Gami" (1856), 327. 

 t49, 227, 228 (1919). 



