70 DARWINIANA. 



effect his own. Or both may have been equally con- 

 versant with the properties of the matter and the 

 relation of the forces concerned (whatever the cause, 

 origin, or nature, of these forces and properties), and 

 the result may have been according to the designs of 

 both. 



As you admit that they might or might not have 

 designed the collision of their balls and its conse- 

 quences, the question arises whether there is any way 

 of ascertaining which of the two conceptions we may 

 form about it is the true one. Now, let it be re- 

 marked that design can never be demonstrated. Wit- 

 nessing the act does not make known the design, as we 

 have seen, in the case assumed for the basis of the argu- 

 ment. The word of the actor is not proof; and that 

 source of evidence is excluded from the cases in ques- 

 tion. The only way left, and the only possible way in 

 cases where testimony is out of the question, is to infer 

 the design from the result, or from arrangements which 

 strike us as adapted or intended to produce a certain 

 result, which affords a presumption of design. The 

 strength of this presumption may be zero, or an even 

 chance, as perhaps it is in the assumed case ; but the 

 probability of design will increase with the particu- 

 larity of the act, the specialty of the arrangement or 

 machinery, and with the number of identical or yet 

 more of similar and analogous instances,, until it rises 

 to a moral certainty i. e., to a conviction which prac- 

 tically we are as unable to resist as we are to deny the 

 cogency of a mathematical demonstration. A single 

 instance, or set of instances, of a comparatively simple 

 arrangement might suffice. For instance, we should 



