442 Anniversary Address by Sir A. Geikie. [Nov. 30, 



MEDALLISTS, 1911. 

 The Copley Medal. 

 The Copley Medal is this year awarded to Sir George Howard Darwin 

 for his long series of researches on tidal theory, including its bearing on the 

 physical constitution of the earth and on problems of evolution in the 

 planetary system. 



As regards the actual oceanic tides, he has perfected the method of 

 harmonic analysis initiated by Lord Kelvin, and has greatly promoted its 

 practical application by the invention of simplified methods of ascertaining 

 the tidal constants of a port from the observations and of framing tide- 

 tables. In another series of researches the tides of a solid planet of slightly 

 viscous material are investigated, including the consequent secular changes 

 in the motion of the planet and of the tide-generating satellite. He traced 

 from this point of view the past history of the earth and moon, and was led 

 to the now celebrated hypothesis that the latter body originated by fission 

 from its primary when in a molten state. 



He has further studied in great detail the classical problem as to the 

 possible figures of equilibrium of a rotating mass of liquid and their 

 respective stabilities, which has engaged in succession the attention of 

 Maclaurin, Jacobi, Kelvin, and Poincare\ The difficult theory of a binary 

 system composed of two liquid masses revolving in relative equilibrium, now 

 known as Eoche's problem, has been greatly developed and extended by him. 

 Such investigations have, of course, an important bearing on the theory of 

 the evolution of the earth-moon system already referred to. 



The above is a mere summary of the main lines of Sir George Darwin's 

 activity. There are in addition a number of highly important memoirs on 

 more or less cognate subjects. Tor example, in dealing with the question 

 as to the degree of rigidity of the earth as it now exists, he has treated it 

 from various points of view; he has considered the theory of the long- 

 period tides, and the stresses produced in the interior by the weight of 

 continents and mountain chains. The inferences of Kelvin and Darwin as 

 to a high rigidity have, it is well known, been recently confirmed in a 

 striking manner by the work of Hecker on the lunar disturbance of gravity. 

 It is to be observed in this connection that Darwin's own early attempts 

 (in conjunction with his brother Horace) to measiire this lunar effect directly, 

 though not immediately successful, have had a great influence on the 

 subsequent history of the subject, as well as on seismometry. 



Mention should also be made of remarkable papers on the history of 



