THE TIDES AND TIDAL ROTATION 



About a century and a half ago the celebrated philo- 

 sopher, Iinmanuel Kant, wrote an essay that has since 

 become classical in which he proved to his own satisfac- 

 tion and to that of the scientific world generally that, 

 owing to the retarding effect of the solar and lunar 

 tides, the earth's day must be gradually growing longer. 

 The arguments advanced by him were purely theoretical, 

 so it was left to others to fortify his conclusions by 

 marshalling physical facts to their support. Accord- 

 ingly, extensive searches were made for records of an- 

 cient eclipses in order to furnish a basis for calculation, 

 and two or three very ancient ones were discovered, 

 which for less delicate work have been found to be in- 

 valuable. In this computation, however, accuracy as 

 to the very days, or even the very hours, was not suf- 

 ficient minutes and even seconds assumed an im- 

 portance. But these latter the records failed to furnish. 

 When the reader then takes into account the further 

 disadvantages that the ancients were dependent on the 

 comparatively crude device of sun-dials for the measure 

 ment of time; that they had not yet learned how to pre- 

 dict solar eclipses and could therefore not have been 

 on the qui mve to note the precise instant of beginning, 



73 



