56 AN INTRODUCTION TO SCIENCE 



only convenient object which he had at hand, his latch-key, 

 his prediction was verified. Inverting the order of his pre- 

 diction on another occasion, it was still verified. The cause 

 of the subject's movements lay not in the thing presented, 

 but in the authoritative suggestion that he would behave 

 towards it in a certain way. Countless claims made by 

 mesmerisers and spiritualistic and theosophical miracle- 

 workers of all grades would fall to the ground if their 

 audiences understood how to devise control-experiments. 

 We have a vivid recollection of the discomforture cf a 

 certain "professor" whose subject could read the Lord's 

 Prayer from a microscopic photograph, could obey the 

 injunctions of his hypnotist when in a separate room, and 

 do many other marvellous things when a small scientific 

 committee eliminated the possibility of suggestion. The 

 droll feature of the performance was the surprise of the 

 "professor," who had deceived himself. He had taken for 

 granted that the effects were caused by the conditions of 

 which he made parade, and not by other conditions which 

 he had overlooked. 



Scientific men are incessantly engaged in testing hypoth- 

 eses by eliminating the condition which, ex hypothesi, is 

 supposed to be the cause of phenomena. Science marches 

 by observing, by colligating observations, by speculating as 

 to the common cause which results in the similarity of the 

 phenomena observed. We often speak of the ingenuity of 

 an hypothesis, but truly this is almost equivalent to assert- 

 ing its falsity or its unnecessary complication and want of 

 finality, if it be not false. The progress of theory is towards 

 unification, and therefore towards simplicity. When, in 

 1859, Darwin published his doctrine of Natural Selection, 

 although he saw that only the fittest can survive, and that 

 the struggle for existence must inevitably eliminate the unfit, 

 he did not realize that this simple theory would suffice to 

 explain all the adaptations to their environment presented 

 by all living things. The eyes in a peacock's tail seemed to 



