[No. 1 



probability that the solid crust, at one or other point, must 

 yield when the strain in the interior increases most rapidly. 



It becomes necessary now to investigate whether the action 

 of the tidal-wave and the alteration in its force is sufficiently 

 great to explain the displacement of the beach-lines. This pro- 

 blem belongs to the science of physical mathematics, and it is 

 not in my line to solve it. I present it as a question to be solved 

 by competent authorities, and restrict myself to the following 

 remarks. 



If the sidereal day was at one time several hours shorter, 

 and the Earth at that period was a solid body, the strain and 

 pressure in the interior would rise with the length of the 

 day until, at last, the strain would be so great that the 

 Earth would begin to yield. It would then accommodate itself, if 

 not entirely, still partially, until the strain was at all events 

 partially relieved. Probably, then, a pause would occur in which 

 fresh strain would accumulate, to produce a new change of form; 

 and these paroxysmal alterations of form, in the body of the 

 Earth, which is strained to its limit of elasticity, probably would 

 take place, when the eccentricity had attained it's highest 

 value, and the strain had increased most rapidly, or at some 

 short time afterwards. In such circumstances, probably, the 

 slight change which the tidal-wave is subjected to on account of 

 the varying eccentricity, may turn the scale and be decisive for 

 the time of the dry land's changes. 



Thomson states (Transact. Geol. Soc , Glasgow 1868) that it 

 is still hopeless to attempt to solve the problem of how speedily 

 the sidereal day becomes lengthened by reason of tidal ac- 

 tion. Experimentally, he calculates (1. c. p. 26) the effect of the 

 present tidal-wave to be so great, that the Earth will in 100 

 years be retarded 180 seconds, corresponding to a prolongation of 

 the sidereal day of 0.01 second, aud if, for the sake of simpli- 

 city, the retarding force is assumed to be constant, the day 

 would thus, at the expiry of 100,000 years (the time that on the 

 average is necessary for an oscillation of the eccentricity), have 

 become 10 seconds longer; and Thomson speaks only of the 



