THE AIM OF SCIENCE 43 



discourse three different meanings of the term 

 " cause" are frequently confused. "A cause may 

 act by impelling, by releasing, or by unwinding. 

 The billiard-ball, that strikes another, determines 

 its movement by impelling. The spark that ex- 

 plodes the powder acts by releasing. The gradual 

 relaxing of the spring that makes the phono- 

 graph turn, unwinds the melody inscribed on 

 the cylinder: if the melody which is played be 

 the effect, and the relaxing of the spring the 

 cause, we must say that the cause acts by un- 

 winding. 



"What distinguishes these three cases from 

 each other is the greater or less solidarity between 

 the cause and the effect. In the first, the quan- 

 tity and quality of the effect vary with the 

 quantity and quality of the cause. In the second, 

 neither quality nor quantity of the effect varies 

 with quality and quantity of the cause: the 

 effect is invariable. In the third, the quantity 

 of the effect depends on the quantity of the 

 cause, but the cause does not influence the 

 quality of the effect: the longer the cylinder 

 turns by the action of the spring, the more of the 

 melody I shall hear, but the nature of the melody, 

 or of the part heard, does not depend on the 

 action of the spring. 



"Only in the first case, really, does cause ex- 

 plain effect; in the others the effect is more or 



