66 SCIENCE PROGRESS 



instability ensues, a cataclysm takes place, the satellite is 

 shot off violently from the parent body, and a new position of 

 stability results with the two bodies in rotation at a certain 

 distance apart, as discussed by Darwin. Thus a consistent 

 theory has at last been obtained, in the formulation of which 

 Darwin's work has been invaluable. Darwin himself regarded 

 his theory as important inasmuch as it was applicable as a 

 whole to celestial evolution. Proven it, of course, cannot 

 be regarded as being, but the evidence in its favour is consider- 

 able. Independent support is now being obtained from the 

 study of spectroscopic binaries , the light curves of many of which 

 can be explained on the supposition that there are two stars 

 rotating around one another and which are under strong tidal 

 distortion. 



The following words from Prof. E. W. Brown's memoir aptly 

 sum up Darwin's service to cosmogony and may fitly close 

 these brief remarks on his work : 



" Perhaps Darwin's greatest service to cosmogony was 

 the successful effort which he made to put hypotheses to the 

 test of actual calculation. Even though the mathematical 

 difficulties of the subject compel the placing of many limitations 

 which can scarcely exist in nature, yet the solution of even these 

 limited problems places the spectator on a height which he 

 cannot hope to obtain by doubtful processes of general reason- 

 ing. If the time devoted to the framing and setting forth of 

 cosmogonic hypotheses by various writers had been devoted to 

 the accurate solution of some few problems, the newspapers 

 and popular scientific magazines might have been less inter- 

 esting to their readers, but we should have had more certain 

 knowledge of our universe. Darwin himself engaged but little 

 in speculations which were not based on observations or precise 

 conclusions from definitely stated assumptions, and then only 

 as suggestions for further problems to be undertaken by him- 

 self or others." 



This paragraph reminds one of the note in the last issue 

 of Science Progress entitled " Great Science and Little 

 Science." Darwin's work did not consist of isolated observa- 

 tions, but is one of the monuments of Science to the making 

 of which his life's work was directed. 



The lectures on Hill's Lunar Theory, which were delivered by 

 Darwin during his tenure at Cambridge of the Plumian pro- 



