HELMHOLTZ IN BERLIN 



yearns to give expression to his feelings in adequate 

 form. To him, possibly, an analysis of how these 

 effects are produced might destroy the charm, and 

 might even lead him to give a wrong interpretation 

 of what was before his eyes, as was the case when 

 Goethe attempted to explain colour by an utterly 

 erroneous conception. But the man of science, who 

 has in him a love of nature, and an imagination akin 

 to that of the poet, and often more penetrating, must 

 strive towards the intellectual satisfaction of under- 

 standing the methods by which nature works. 



In one of his papers on hydrodynamics, Helmholtz 

 refers shortly to the theory of tidal action. The 

 tendency of tidal movements on the surface of a planet 

 is to retard its rotation till at last it turns always the 

 same face to the body that causes the tidal motion. 

 Helmholtz was the first to point out that the reason 

 why satellites generally turn the same face to their 

 primary, is to be found in the tides produced by the 

 primary on the satellite while it was yet in the molten 

 state. 1 



The movements of glaciers and the formation of 

 ice arrested his attention, and it so happened that at 

 that time the observations of Rendu, Forbes and 

 Tyndall were being discussed. Helmholtz's contribu- 

 tions to the ice theory were published in 1865 and 1866, 

 while he was in Heidelberg. Faraday had made the 

 familiar observation that two pieces of ice pressed against 



1 Tait, Thermo-DynamicSy p. 104. 

 221 



