CAUSE AND EFFECT— PROBABILITY 135 



walk round so that a line drawn from the stone to me 

 sweeps out equal areas in equal times, a fundamental 

 characteristic of the laws of planetary motion. Now my 

 motion might be very fairly described by the law of 

 gravitation, but it is quite clear that no force from the 

 stone to me, no law of gravitation, could logically be said 

 to cause my motion in the ellipse. We might in imagina- 

 tion conceive a point changing its motion according to the 

 law of gravitation and tracing out my ellipse ; it might 

 keep pace with me, and would, of logical necessity, cover 

 equal areas in equal times. This logical necessity would 

 flow from our definition, our conception, namely, that of a 

 gravitating point. This point might be used to describe 

 my elliptic motion, and to predict my positions in the 

 future, but no observer would be logical in inferring 

 that the necessary sequence of positions involved in the 

 concept of a gravitating point could be transferred, or pro- 

 jected into a necessity in the sequence of his perceptions 

 of my motion. I might go round the ellipse a hundred 

 times in the same manner and then stop or go off in an 

 entirely different path. The sole legitimate inference of 

 the observer would then be that the law of gravitation 

 was not a sufficiently wide-embracing formula to describe 

 more than a portion of my motion.^ This difference 

 between necessity in conception and routine in perception 

 ought to be carefully borne in mind. The corpuscular, 

 the elastic- solid, and the electro -magnetic theories of 

 light all involve a series of conclusions of logical necessity, 



1 The example cited is given by Mr. Stuart on p. i68 of his Chapter of 

 Science. It is there used to support the argument of primitive man ; my will 

 causes me to go round the ellipse, therefore will causes the planets to go round 

 in ellipses, and hence Mr. Stuart passes to Aristotle's God as continual mover 

 of all things. That will is only found associated with certain types of material 

 nervous systems is not used by Mr. Stuart, however, to logically infer the 

 material nature of his first cause. He passes by the juggle of a common name 

 from the known to the unthinkable outside the sphere of knowledge and 

 science. The real truth which his Chapter of Science contains as to the 

 characteristics of natural law is hopelessly vitiated by his theological stand- 

 point. " I know," he says, " no result of science which could go to discredit 

 any single thing in all the Bible" (p. 184). Mr. Stuart's "science" is thus 

 incomparably more retrograde than the modern Cambridge theology which 

 discredits Noah's Ark. 



