Prksidknt's Addhess — >Skct. a. 29" 



We have iu»\v to deal with the eonchuUug pDi'tioii of tliis ah-eady 

 too long address, viz. : — 



Prohlkms akisin(; out ok Vakiaijlk Stah Hkskaiuui. 



To do this poitioii of in}' pajier anything hke justice would neces- 

 sitate nioi'e time and space than 1 can rightly demand. For it is nob 

 claiming too much for the subject that t have brctught before your 

 attention this morning, that it has opened up more problems in 

 astronomy, problems in stellar evolution, stellar devolution as well as 

 stellar physics, than any other branch of astronomical research. 



In the forefront of the problems urging themselves on our con- 

 sideration is that of tidal deformation. If two bodies revolve round 

 one another in contiguity it is evident that the tidal deformation of 

 both must be enormous. Darwin in his classical researches has demon- 

 strated theoretically what the shape of two stars would be which 

 circled round one another practicallj' in contiict. 



It is possible, I think, by means of very accurate observati<jn to 

 determine how far Darwin's remarkable conclusions find expression in 

 the actual realities of close binary movement. Already there is evi- 

 dence of the closest agreement 1)etween theory and observation. 



But, further, the generation of vast tides by the mutual attraction 

 of two contiguous masses of matter means the recession of the revolving 

 bodies, a recession growing gradually less as the distance between the 

 components increases, inasmuch as the amount of tidal deformation is 

 in the inverse ratio of the cubes of the distance of the deforming 

 bodies. 



Thus in every Algol system we have the embryonic stage of our 

 earth-moon system. And it is matter for grave satisfaction that in the 

 case of two Algol stars, j^ Lyrae and V Puppis, we ha\e incon- 

 testible e\ idence of this very recession which Darwin years ago, from 

 theoretical considerations alone, indicated to be the outcome of tidal 

 deformation. 



Then the extraordinary phenomenon of two stars revolving in 

 contact opens up a wide field "of conjecture and inquiry. A deter- 

 mination of the light changes, due to eclipse, of any binary system, 

 enables us also to obtain some idea of the density of the system, and 

 when spectroscopic measures are also available, of the size and mass of 

 the component stars. 



In this \\'A\ we have been able to arrive at the conclusion that the 

 density of all Algol stars is very much less than that of water, the 

 average density of those known comes out at about one-eighth. This 

 is in complete accordance with what we would expect. 



Algol stars are at the beginning of things stellar. They are at 

 the earliest stages of a long evolution. That at this point of their 

 history they should be distinctly gaseous is only what their evolution 

 postulates. Only as gaseous orbs of extreme tenuity could they come 

 into being at all. 



Granted this gaseous conditif)n, granted their bifurcati()n into twa 



