314: ILLOGICAL GEOLOGY. 



the Earth in circles, said the earliest observers : led partly 

 by the appearances, and partly by their experiences of cen 

 tral motions in terrestrial objects, with which, as all circu 

 lar, they classed the celestial motions from lack of any 

 alternative conception. Without this provisional belief, 

 wrong as it was, there could not have been that compari 

 son of positions which showed that the motions arc not 

 rcpresentable by circles; and which led to the hypothesis 

 of epicycles and eccentrics. Only by the aid of this hy 

 pothesis, equally untrue, but capable of accounting more 

 nearly for the appearances, and so of inducing more ac 

 curate observations only thus did it become possible for 

 Copernicus to show that the heliocentric theory is more 

 feasible than the geocentric theory ; or for Kepler to show 

 that the planets move round the sun in ellipses. Yet 

 again, without the aid of this approximate truth discovered 

 by Kepler, Xewton could not have established that general 

 law from which it follows, that the motion of a heavenly 

 body round its centre of gravity is not necessarily in an 

 ellipse, but may be in any conic section. And lastly, it 

 was only after the law of gravitation had been verified, 

 that it b.ecame possible to determine the actual courses of 

 planets, satellites, ami comets; and to prove that, in con 

 sequence of perturbations, their orbits always deviate, more 

 or less, from regular curves. Thus, there followed one 

 another live provisional theories of the Solar System, 

 before the sixth and absolutely true theory was reached. 

 In which live provisional tin-ones, each for a time held 

 as final, we may trace both the tendency men have to 

 leap from scanty data to wide generalizations, that are 

 either untrue or but partially true; and the necessity 

 there is for these transitional generalizations as steps to the 

 final one. 



In the progress of geological speculation the same laws 

 of thought are clearly displayed. We have dogmas thai 



