44 INTRODUCTION TO SCIENCE 



less given in advance, and the antecedent in- 

 voked is in different degrees, of course its 

 occasion rather than its cause." 



In the first case, where the cause acts by im- 

 pulsion, what is in the effect was already in the 

 cause; the momentum of the one billiard-ball 

 passes in great part into the other; the causal 

 explanation is complete. 



In the second case, where the cause acts by 

 releasing, it is an indispensable condition; it 

 pulls the trigger apart from which the effect will 

 not occur. But it does not explain the effect. 

 The egg of a sea-urchin will develop without 

 being fertilized if it be immersed for a short time 

 in sea-water to which some magnesium chloride 

 or the like has been added, and there are many 

 other ways of inducing "artificial parthenogene- 

 sis." But the cause in this case in only a trigger- 

 puller. 



In the third case, there is more than trigger- 

 pulling, but the cause does not explain more 

 than the rate or duration of the effect. 



People are wont to recognize themselves as the 

 "causes" of this or that result, congratulating 

 themselves on being the "happy cause of success," 

 blaming themselves as being the "unfortunate 

 cause of disaster," and this idea of an active agent 

 effecting a change in something passive often 

 influences the popular conception of causality. 



