g^O K THE 



'south AFRICAN JOURNAL 

 OF SCIENCE: 



COMPRISING THE REPORT OF THE 



SOUTH AFRICAN ASSOCIATION 



FOR THE 



ADVANCEMENT OF SCIENCE, 



1920. 



BULAWAYO. 



OFFICERS: 1S20-1921. 



PRESIDENT. 

 Prof. J. E. DUERDEN, M.Sc., Ph.D., A.R.C.S. 



VKJE-PRESIDENTS. 



I'rof. G. E. Cory, M.A. 



Prof. R. Lkslik, M.A., F.S.S. T. R. SiM, D.Sc. 



Prof. J. A. Wilkinson, M.A. F.C.S. 



HON. GENERAL SECRETAKIES. - 

 H. E. Wood, M.Sc. F.R.A.S., Union Observatory, Johannesburg. 

 C. F. JuRlTZ, M.A., D.Sc, F.I.C., Agricultural Chemical Rescarcli li'aboratory, Capetown. 



HON. GENERAL TREASURER. 

 J A. FooTE, F.G.S., F.E.I.S., Conuuercial High School, Johannesburg. 



HON. LIBRARIAN. 

 Annie Porter, D.Sc, South African Institute for Medical Research, Johannesburg. 



ASSISTANT GENERAL SECRETARY. 

 H. A. G. Jeffreys, O.B.E., Box 6894, Johannesburg. Telegraphic Address: "Science." 



HON. EDITOR OF JOURNAL. 

 Prof. H. B. Fantiiaji, M.A., D.Sc, University College, Johannesburg. 



VOL. XVII. JULY. J192A. NO S. 3 a nd 4. 



JOHANNESBURG. 

 PUBLISHED BY THE ASSOCIATION. 



1921. [Price lOs 



