1889.] THE DISPLACEMENT OF BEACH-LINES. 13 



some time in the distant future, come always to present the same 

 side to the Moon. This view of Kant's is adopted as correct by 

 the leading modern physicists; by such men as Robert Mayer, 

 HdmhoUg and W. Thomson. 



There are certain relations connected with the movements 

 of the Moon, which astronomers are disposed to explain by the 

 assumption that the sidereal day slowly increases, owing to 

 the friction of the tidal-wave. But on these subjects we will, 

 here, only refer the reader to Thomson and Taifs „ Treatise 

 of Natural Philosophy" and to a Paper by the first-named: „On 

 Geological Time" (Transact. Geol. Soc. Glasgow, 1868. Vol. Ill, 

 Part I, p. 1 ff.). 



Thomson and Tait, in their Natural Philosophy, treat of 

 the rotation of the Earth. They state that there are various 

 forces acting to change it; some of these act towards making 

 the sidereal day shorter, whilst others, again, act in the opposite 

 direction. The latter forces are the most powerful, and among 

 them, again, the tidal-wave undoubtedly takes the most impor- 

 tant place; so that for that reason the day becomes always 

 longer and longer in the course of time. The cooling is the 

 most impoitant force that contributes to abbreviate the day, 

 but its effect is estimated by Thomson (Transact. Geol. Soc. 

 1. c. p. 28) at only ^notr part of that of the tidal-wave; 

 and the effect of the latter can not be counterbalanced by 

 any of the other forces which act, sometimes in one and some- 

 times in another direction (transport of sediments from higher 

 to lower latitudes, or vice versa, accumulation of ice at the 

 poles and similar causes), and which in the course of time 

 abolish themselves, whilst the tidal-wave always acts for milli- 

 ons of years in the • same direction, {Thomson: Of Geological 

 Dynamics, Transact. Geol. Soc. Glasg. 1869. Vol. Ill, part 2, 

 p. 223). 



In that way the sidereal day should always, therefore, be- 

 come longer and longer. Now, what influence has that upon the 

 Earth? If the Earth was entirely fluid, it is clear that it would 

 immediately be compelled to change its form. According as the 



