32 POPULAR LECTURES AND ADDRESSES. 



round its axis, and lengthen the duration of the 

 da}'. That there is such a tendency has lone; 

 been known to philosophers of the more abstract 

 kind. It is difficult to say who first promulgated 

 this idea. It has been recently stated that the 

 metaphysician Kant first asserted that the earth's 

 rotation is diminished through the influence of the 

 tides. This I know for certain, that the idea was 

 first given to me by my brother, Professor James 

 Thomson. As long ago as the first meeting of the 

 British Association in Glasgow, 1840, he pro- 

 pounded as a necessary result of the theory of 

 energy, that friction of the tides in channels 

 must give rise to a loss of something then called 

 7v>-:vVv7, from the motion of the earth and the 

 moon. More recently published articles, and 

 especially those of Mayer, the great German 

 advocate of the modern theory of heat, who did 



much to urge the reception of the idea of 

 an equivalence between heat and mechanical 

 .power, point out that the rotation of the earth 

 must be diminished by the tides. 



14. But we may go further, and say that tidal 



