EVOLUTION AND THEISM. 385 



and the first half of the present were exercised, as to its real 

 nature. While Hume and his followers admitted nothing but 

 invariable and unconditional antecedence, as the "cause" of a 

 phenomenon, excluding altogether that notion oi force or power 

 which was expressed by the term "efficient cause," there has 

 always been a school of scientific men, who have maintained that 

 this notion is not only accordant with the fundamental instincts 

 of the human mind and the uniform teachings of human experi- 

 ence, but is justified by the highest scientific reasoning. And I 

 hold it to be not the least of the vast services rendered to science 

 by Sir John Herschel, that by constantly keeping this great 

 principle in clear view, he prepared the way for that general 

 recognition of it, which has latterly come about almost insensibly, 

 as a result of those researches into the mutual relations of the 

 physical forces, which have culminated in the general doctrine of 

 the Conservation of Energy. For even John Stuart Mill, who was 

 the most powerful upholder of the Hume doctrine, had come, in 

 his later years, to perceive (what I had frequently urged upon him 

 at an earlier period) that when the assemblage of antecedents is 

 analyzed, they are always found resolvable into two categories — 

 the force or power which produces the change, and the material 

 collocations which constitute the conditions of its exercise. Thus 

 — to use one of Mill's own illustrations — although we speak of 

 a man's fail from a ladder as " caused " by the slipping of his ibot 

 or the breaking of a rung (as the case may be), the efficient cause 

 is the attractive force of the earth, which the loss of support to 

 the man's foot brings into operation. And now that heat, light, 

 electricity, magnetism, chemical affinity, and vital agency, are 

 universally admitted to be only varied expressions of different 

 kinds of movement among the particles of matter, sustained by 

 the same agency as that which, when it acts on masses of matter, 

 produces or resists mechanical motion, the " efficient cause " of 

 every phenomenon in nature is sought in the action of one or 

 other of these forces, and the determination of the conditions of 

 that action becomes the primal object of scientific inquiry. 



The first result of thisstudy is the recognition of uniformity 

 in the action of these forces ; like results happening under like 

 conditions ; and diversities in the conditions being attended with 



