158 ■ SECULAR CHA^UE IN THE I'KklOD OF L CARIN.H. 



Of the direct and immediate cause of such variation of 

 period as that of U Carinae we know practically nothing". 



When a period is uniformly increasing or decreasing, one 

 of two causes may be in operation, or perhaps both. The 

 matter of the star may be growing steadily less in bulk, due to 

 the constant attrition of a near companion. 



Or tidal friction, due to the mutual attraction of the two 

 bodies, may accelerate or retard the period of revolution, accord- 

 ing to the relation of the period of revolution to the period of 

 rotation of the component stars. 



But where the variation is circular in character, there is 

 more difficulty in reaching a reasonable explanation. 



If we imagine the orbit of the binary star to be sensibly 

 elliptical, then l)inary rcA-olution, >vith its corres])onding tidal 

 action, must produce certain changes in the form of the 

 orbit. These changes will become manifest in an alteration 

 in the light period of the star. 



Or we imagine such a system a.-^ U Carin?e to revolve 

 round a large and central body in a period of 19 years. The 

 variation in |)eriod, 0.65 day, would then be a measure of the 

 radius of the system. 



The difficulty here is that we have to imagine a central 

 body three thousand times more bulky than the sun. 



Whatever be the explanation, we are at present only groping 

 dimly towards it. But we are sure of this, that the facts we 

 obtain will one day be of service in definitely ascertaining and 

 defining the causes which produce variation in tlie period of sucl'. 

 stars at U Carinie. 



It is in this expectation that the present brief exposition of 

 the light changes of L' Carin?e are offered. 



Active Principles of South African Plants. 



— The South African Medical Record, of i.^th November* con- 

 tains a paper read by Dr. C. F. Juritz before the British Medical 

 As.sociation, Cape of Good Hope (Western) Branch, on the 27th 

 August, on " The urgency of a definite forward movement in the 

 study of the active principles of South African Plants." 



Radium in Japan, — Dr. Ishidzu, of the Tokyo Hy- 

 gienic Laboratory, has been investigating the hot and mineral' 

 springs of fapan with a view to ascertain the quantities of radiuni 

 which they contain. It is reported that, as a result of his investi- 

 gations, he considers Japan to be the richest radium countrv in 

 the world. Considerable proportions of radiuni are declared by 

 Dr. Ishidzu to be present in the waters of a mineral spring in 

 the Yamanashi Prefecture, and radium-bearing water also occurs 

 in another spring at Chuggoka. 



*(1915) 13 [21]. 



