THE PSYCHOLOGY OF BELIEF. 237 



de])end on the convergence of a number of separate probabilities 

 towards a common centre, while none of them are complete as 

 proofs ; the whole of what is commonly termed "circumstantial" 

 evidence being, in fact, of this character. And just as the value 

 of the " circumstances " depends on the testimony of experts, — 

 a case of poisoning, for example, requiring the analysis of the 

 chemist, and the examination of the morbid appearances by a 

 pathologist, — so must the hypothesis of evolution be ultimately 

 either established or disprovetl by its accordance or disaccordance 

 with a vast aggregate of facts of Nature, which belong to different 

 departments of scientific inquiry. The geologist traces the suc- 

 cession of plants and animals in palseontological order, and finds, 

 as he advances in his studies, less and less evidence of interrup- 

 tion, and more and more of continuity, biological as well as 

 physical. The zoologist and botanist, who have been accustomed 

 to classify their multitudinous and diversified forms of plants and 

 animals according to their " natural affinities," find a real meaning 

 in their classification, a new significance in their terms of relation- 

 ship, when these are used to represent what might be regarded 

 with probability as actual community of descent. The morpho- 

 logist who has been accustomed to trace a " unity of type " in 

 each great group, and especially to recognize this in the presence 

 of rudimentary parts which must be entirely useless to the animals 

 that possess them, delights in the new idea which gives a perfect 

 rationale of what had previously seemed an inexplicable super- 

 fluity. And the embryologist, who carries back his studies to the 

 earliest phases of development, and follows out the grand law of 

 Von Baer, " from the general to the special," in the evolution of 

 every separate type, finds the extension of that law from the indi- 

 vidual to the whole succession of organic life, impart to his soul 

 a feeling of grandeur, like that which the physical philosopher 

 of two hundred years ago must hive experienced, when Newton 

 first promulgated the doctrine of universal gravitation. And 

 lastly, when the doctrine of evolution is looked at in its moral 

 aspect, as one which leads man ever onwards and upwards, and 

 which encourages his brightest anticipations of the ultimate 

 triumph of truth over error, of knowledge over ignorance, of 

 right over wrong, of good over evil, who shall presume to say 



