Stoney — Natural Science and Ontology. 511 



of cause and effect. There is nothing in Nature competent to cause 

 one body to exclude another from the space it occupies. A state- 

 ment of the fact is one of the laws of Nature. If a stone be allowed 

 to drop in the vicinity of the earth, its downward speed is accelerated 

 by a perfectly definite law. This law is one of the Uniformities of 

 Nature 1 which scientific inquiry has brought to light. But tvithin 

 the domain of Physics there is no cause of the acceleration. (See 

 § 25, p. 482, and Diagram IV., p. 487.) The facts as to what occurs 

 in Nature can be observed ; the circumstances under which they 

 occur can be investigated ; similar cases can be compared ; and 

 the laws to which the simultaneous or successive events conform 

 may be brought to light. But here our knowledge ends : Physical 

 Science has said its utmost. 



Now all this is changed when we turn to the only field of ob- 

 servation accessible to us in which we are dealing directly with auta. 

 The thoughts of which I consist, the thoughts that are my mind, 

 are auta : a very small group of auta no doubt in the mighty uni- 

 verse of auta, but still an actual sample, although a very special and 

 one-sided sample of what auta are. Now in the operations that go 

 on in my mind I do find instances, some few instances, of causes pro- 

 ducing effects. The familiar case of a geometrical demonstration 

 producing in a man's mind a belief in the truth of the conclusion is 

 a case in point. Here the understanding of the proof is the efficient 

 cause of the belief in the conclusion which accompanies that under- 

 standing. A wish to accomplish something, and a knowledge of 

 how to go about it, both of which are thoughts in the mind, are a 

 part of the efficient cause of subsequent events, unless counteracted 

 by other causes. A few other examples can be obtained from the 

 same small field of investigation ; and this is all that man, in his 

 isolated position, has any right to expect ; for the bulk of his 

 thoughts are due, at least in large part, to autic causes which lie 

 outside his mind, and it is there also that those of his thoughts that 

 are known to be causes, usually exhibit their effects. When per- 

 ceptions arise in my mind, the effect is indeed within my mind, but 

 the cause lies beyond it ; and when I move my muscles the cause is 

 within my mind, but it is outside the mind that it operates. The in- 

 stances are indeed few where the causes and the effects are both within 



1 In this case the vicinity of the earth to the stone and the acceleration of the 

 stone's vertical velocity are the two " unfailingly concomitant events." 



