348 THE EVOLUTION OF LIFE. 



tion as the law of many diverse orders of phenomena, has 

 been spreading ; may we not say that there thence arises the 

 probability that evolution will presently be recognized as the 

 law of the phenomena we are considering ? Each further ad- 

 vance of knowledge, confirms the belief in the unity of 

 Nature ; and the discovery that evolution has gone on, or is 

 going on, in so many departments of Nature, becomes a rea- 

 son for believing that there is no department of Nature in 

 which it does not go on. 



§ 118. The hypotheses of Special Creation and Evolution, 

 are no less contrasted in respect of their legitimacy as hy- 

 potheses. While, as we have seen, the one belongs to that 

 order of symbolic conceptions which are proved to be illusive 

 by the impossibility of realizing them in thought ; the other 

 is one of those symbolic conceptions which are more or less 

 completely realizable in thought. The production of all 

 organic forms by the slow accumulation of modifications upon 

 modifications, and by the slow divergences resulting from 

 the continual addition of differences to differences, is mentally 

 representable in outline, if not in detail. Various orders of 

 our experiences enable us to conceive the process. Let us 

 look at one of the simplest. 



There is no apparent similarity between a straight line 

 and a circle. The one is a curve ; the other is defined as 

 without curvature. The one encloses a space ; the other 

 will not enclose a space though produced for ever. The one 

 is finite ; the other may be infinite. Yet, opposite as the 

 two are in all their properties, they may be connected together 

 by a series of lines no one of which differs from the adjacent 

 ones in any appreciable degree. Thus, if a cone be cut by 

 a plane at right angles to its axis, we get a circle. If, instead 

 of being perfectly at right angles, the plane subtends with 

 the axis an angle of 89° 59', we have an ellipse which no 

 human eye, even when aided by an accurate pair of compasses, 

 can distinguish from a circle. Decreasing the angle minute 



