DISCOVERY BY MEANS OF INFERENCE. 605 



inheritance, selection, and adaptation. Whilst persons in 

 general consider incredible the hypothesis that, during an 

 immense number of years, man was gradually developed 

 from the form of an ape, they are familiar with and believe 

 the far more wonderful fact that, even in the comparatively 

 short space of twenty years, each individual man is de- 

 veloped from a mere speck of albuminous matter. It is 

 intrinsically no more incredible that, during an immense 

 series of ages, inorganic, inanimate matter gradually 

 becomes organised, acquires animation, and, by means of 

 the processes of inheritance, selection, and adaptation, 

 gradually developes, and passes through a whole series of 

 vegetable and animal forms of life, up to that of a man, 

 than that dead matter, partly organic and partly in- 

 organic, taken as food and air by a woman, becomes in a 

 few hours a part of her living structure, in a few months 

 an embryo child, which by further assimilation of dead 

 material becomes in a few years a full-grown human being. 

 In mental physiology, as well as in the physical and 

 chemical sciences, in biology, &c., discoveries have been 

 made, not only by means of experiment, observation, and 

 comparison, but also by means of inference ; and those 

 made by the latter method have usually been the most 

 abstruse and important. The process of inference, based 

 upon comparisons of the actions of mental power and of 

 those of the physical forces, leads us to conclude that even 

 the human mind acts in accordance with all the chief 

 laws and principles of tnose forces ; also that neither the 

 conscience nor the will is a separate or distinct mental 

 power or faculty, and that the latter is simply a conscious 

 mental effort to effect an object, the idea of which is 

 already present to the mind. 1 



1 See pp. 127-132. 



