XXXVI SOUTH AFRICA MEDAL. 



but were written in April of that year ; they were printed next to 

 Mr. H. N. Russell's paper on the same subject, which was, how- 

 ever, only written in October. It thus appears that both authors 

 nearly simultaneously and quite independently found out that it 

 was possible, in the case of an Algol star, to deduce a limiting 

 value for its mean density. Dr. Roberts's result for the four 

 stars he considered showed that the average density of a close 

 Algol variable is only 0.13 (say one-eighth) that of the Sun, and 

 Mr. Russell summarizes by saying : ' Notwithstanding the causes 

 of uncertainty, it is evident that the Algol variables as a class 

 are much less dense than the Sun, probably less than one-fourth 

 as dense.' 



" These distinguished achievements make it unnecessary to 

 do more than just to mention that Dr. Roberts is himself a dis- 

 coverer of many variable stars, and that he has investigated the 

 periods of southern variable stars and published the results in a 

 well-known catalogue. 



" Our medallist's assiduity and single-heartedness in his 

 astronomical work would alone have entitled him to our con- 

 sideration. We are grateful that, in addition to those good 

 qualities, we have been able to recognise the spark of genius. 

 Dr. Roberts, in the name of the Association, it gives me pleasure 

 to present to you this our medal, and our best wishes for the 

 successful continuation and fruition of your valuable work 

 accompany it." 



Dr. Roberts, in expressing his thanks, said that he felt it a 

 great honour that the Association should single him out in this 

 way. It was an extreme pleasure to him to be regarded as one 

 of the astronomers of the country, and he was proud, as an 

 amateur, to belong to that body. He would be glad if the honour 

 which had come to him would be the means of inducing others to 

 give up a portion of their time to the study of one or other of 

 the sciences. He felt specially honoured in that this mark of the 

 Association's appreciation had been presented to him by so dis- 

 tinguished a scientist as the President. 



Previous Recipients. 



1908. Grahamstown. — Arnold Theiler, C.M.G., M.D., Bacterio- 



logist to the Transvaal Government, Pretoria. 



1909. Blocmfontein. — Harry Bolus, D.Sc, F.L.S.. of Sher- 



wood, Kenilworth, Cape Division. 



1910. Cape Town. — John Carruthers Beattie, D.Sc, F.R.S.E., 



Professor of Physics. South African College, Cape 

 Town. 

 KHi. Bulawayo. — Louis Peringuey, D.Sc, F.E.S.. F.Z.S.. 

 Director of the South African Museum. Cape 

 Town. 



