10 president's address. 



in conception between estimating the length of a standard roc! 

 and spanning a universe. The humble student toiling at some 

 laboratory analysis is an arm in the same service that seeks to 

 explore the remotest distances, lay bare the most hidden secrets, 

 declare the foundational laws that govern this manifold, many- 

 mirrored universe. There is no isolated labour under the sun. 

 The long series of observations of the moon, discussed and 

 worked into theory by Xeison of Natal, though long unused, has 

 now found its fitting place in a new theory of the moon's motion. 

 This new theory brings into pre-eminence a consideration of tidal 

 retardation, and the consequent slowing down of the earth on its 

 axis. And at this point we reach another aspect of astronomical 

 research, that which deals with the life history of our own good 

 green earth. It would seem a very far cry to relate all this lunar 

 work to the winking changes ■^een in a variable star. One man 

 works at the moon's position, and evolves a theory of its move- 

 ments ; another finds that this theory means a slowing down of 

 the earth on its axis and an outward spiral movement — slow with 

 the terrible patience of Nature — of the moon's path ; and yet 

 another, examining some far-ofif binary star, finds its period of 

 revolution increasing in the process of the years. Then comes 

 the unifying touch, and all this i'^ seen to be part of one great 

 whole, to which each worker has added his part. 



The study of variation in the brightness of stars, due either 

 to eclipse, or to some condition of orbital motion, or to intrinsic 

 light changes in the star itself, has been especially studied in 

 .South Africa. We have already referred to Innes's work, as 

 embodied in the Annals of the Cape Observatory, Vol II, and in 

 many of the Circulars of the Union Observatory. 



At Lovedale, the work undertaken during the past twenty 

 years has been the systematic recording of the changes in bright- 

 ness of over a hundred well-known stars. I do not mean here to 

 do aught but refer to the bigger issues which this long series of 

 observations has revealed, and I do so because of my desire to 

 give weight to the thought of the unity of all scientific efifort. 



A study of the light variation of certain eclipsing stars 

 yields not only the form and nature of the orbit in which they 

 move but also the shape, density, and relative size of the com- 

 ponent stars. It will readily be seen that such deductions, if 

 reasonably substantiated, have an important bearing on the ques- 

 tion of stellar evolution. 



That eclipsing stars are very probably in the early stages of 

 their life history, seems -e reasonable conclusion ; thus any facts 

 that emerge regarding their form, or structure, or density are of 

 no ordinary interest. It is of importance to note that every close 

 binary star is of a density many tunes less than that of the sun ; 

 that few of them reveal an outer atmosphere ; that the oblate- 

 ness yielded by an examination of their light curve is in close 



