582 



Proceedings of the Royal Irish Academy. 



erroneous mechanical and physical assumption which asserts that the 

 particles of the solid shell retained the same places which they held 

 when they were liquid. When a solid, continuous shell had heen 

 once formed, it is manifest that it would constitute for the liquid 

 nucleus, and the semi-liquid matter passing into the solid state, a 

 casing far less yielding than the substances enclosed within it. These 



Fis. 1. 



plastic substances would, as I have already pointed out, tend to freely 

 arrange themselves according to the hydro-dynamical laws ; and thus 

 the arrangement of the strata of the shell and nucleus above indicated 

 must necessarily follow. Each successive stratum added to the shell's 

 inner surface by solidification from the nucleus would be moulded 

 against the existing shell into a shape corresponding to that of the 

 surface of the fluid mass. 



The plastic character of solids shown by the effect of the die on 

 medals, the forcing of solids under pressure to change shape, has led 

 to the inference that the earth and planets may have acquired their 

 oblate figures without ever having been fluid. 



This fallacy arises from observing solids 'jon the earth's surface 

 acted on by gravity. A solid sphere of lead, ten feet in diameter, 

 placed on a flat place, would probably be slightly flattened, and its 

 poles become less than its equivalent ctiameter. But if so, the result 

 would be due to the action of parallel forces. The diagram (fig. 2) 

 represents the sphere acted on by this force, and (fig. 3) the same 

 sphere acted on only by the force of attraction directed to its centre, C. 

 The resulting effects in both cases would be totally different. 



The force resulting from an angular velocity such as in the earth 

 would be only s^ia-th of the parallel forces in the first case. The force 

 resulting from this cause would be so small as to have no sensible 

 effect except on extremely yielding masses, such as liquids. All 

 experiments on solids at the earth's surface are illusory on account of 

 the parallel action of gravity when applied to such matter. A round 



