FIFTH AWARD OF THE SOUTH AFRICA MEDAL AND 



GRANT. 



{Fund raised by Members of the British Association in com- 

 memoration of their visit to South Africa in 1905.) 



Dr. Alexander Roberts, F.R.A.S., F.R.S.E., was nomi- 

 nated for the award upon the following grounds : — 



" For the past twenty years Dr. Roberts has devoted all the 

 time which he was able to spare from his responsible duties at 

 Lovedale, to the study of variable stars and kindred astronomical 

 work. 



" Beginning in 1891 with no other equipment than an old 

 theodolite and an opera glass, he made a survey of the southern 

 sky south of declination 30 , and, in spite of the slender resources 

 at his disposal, was rewarded by the discovery of twenty variable 

 stars in the course of the next two or three years. 



" Notable as this result of statistical research in itself was 

 in regard to our knowledge of the structure of the universe, it 

 constituted for Dr. Roberts only the first stepping-stone towards 

 a sphere of scientific work of a far more general and important 

 character. Henceforth he devoted his energies to a detailed 

 examination of the light curves of variable stars, a research 

 rendered possible by the presentation of a new equatorial tele- 

 scope especially designed for this class of work. 



" He at once clearly recognised the importance of a detailed 

 study of the so-called Algol variables from the standpoint of 

 cosmical evolution. 



" The light fluctuations of these variables are now known 

 to be caused by eclipse phenomena recurring at regular intervals 

 owing to the revolutions of two stars round a common centre of 

 gravity, the plane of orbital motion being so situated that the 

 light of one star is eclipsed in the direction of the line of sight 

 by the other. 



" Not only did he contribute more than any other observer of 

 variable stars to the knowledge of facts, but he applied his great 

 mathematical abilities to the consideration of the physical causes 

 underlying these light phenomena, and developed a mathematical 

 theory which enabled him to determine the density and figure of 

 the two components and also their orbital motion. 



: ' This unique combination of observational skill with a 

 clear insight into the theoretical vistas of the problem has 

 resulted in the production of over 100 important contributions to 

 scientific journals, giving Dr. Roberts world-wide reputation as 

 an astronomer. It would be impossible to enter fully upon the 

 public appreciation of his scientific work, but I may be allowed 

 to quote the following remarks by two of our leading scientists. 



" In his presidential address to the British Association at 



