IS DEVELOPMENT HYPOTHESIS SUFFICIENT? 91 



era of which it cannot be deprived, and which cannot be added to nor 

 lessened. It is this that secures the permanence of Nature, keeping it 

 unchanged in its power or powers amid all changes of action. This 

 energy, disappearing in one form, appears necessarily in another, and 

 gives us what Spencer calls the " persistence of force." This ever- 

 enduring force gives rise to development. Going out from one body, 

 it is manifested in another. The fact is, all causation, all physical 

 action, is evolution. The substances and powers in the agents acting 

 as the cause are found, though in a modified form, in the effects. Pro- 

 ceeding on this very principle, Mayer says : " Forces are causes ; ac- 

 cordingly, we may in relation to them make full application of the 

 principle causa equat effectwn" and he thus elaborated the grand sci- 

 entific truth, the most important discovered in our day, that the sum 

 of energy in the universe is always the same. 



2. I admit that this power becomes more and more differentiated, 

 that is, takes more and more diverse forms, and thus imparts an ever- 

 increasing multiplicity and variety to the universe, and will continue to 

 do so till the diversity breaks it up, and " the heavens shall pass away 

 with a great noise, and the elements shall melt with fervent heat, the 

 earth also, and the works that are therein shall be burned up." Mr. 

 John S. Mill has been successful in showing that there is usually more 

 than one antecedent or agent in a cause. " A man takes mercury, goes 

 out-of-doors, and catches cold. We say, perhaps, that the cause of his 

 taking cold was exposure to the air. It is clear, however, that his 

 having taken mercury may have been a necessary condition of his 

 catching cold ; and though it might consist with usage to say that 

 the cause of his attack was exposure to the air, to be accurate we 

 ought to say that the cause was exposure to the air while under the 

 effect of mercury." He concludes, " The real cause is the whole of 

 these antecedents." Now, I hold that in physical Nature causes are 

 not only usually, but invariably, of this dual or plural nature. I go a 

 step farther, and have shown, I think, that the effects are also of the 

 same dual or plural character. The effect, in fact, consists of the 

 same agents or substances as the cause, but now in a new state. A 

 picture falls from a wall and breaks a table ; we say that the breaking 

 of the table was the effect of the fall of the picture. But the true 

 effect embraces both the picture and the table, the picture having lost 

 its momentum, and the table being broken. It follows from all this 

 that the new combination of agents, acting as the causes, must produce 

 more and more varied effects, as the effects joining with other effects 

 become causes, and ramify into branches and branchlets. The sum 

 of the powers is one and the same, but they appear in an ever-increas- 

 ing number and diversity of forms. The conservation of force thus 

 gives a unity to Nature, while the mutual action and interaction give 

 it its multiplicity. I remember how deeply I was interested in that 

 paper (I read it when it appeared) of Yon Baer, in which he shows 



