AIM AND PEOGRESS OF PHYSICAL SCIENCE. 389 



has reached the highest grade and excited the greatest 

 admiration, namely, in the region of mental perception, 

 that, as the latest results of physiology teach us, this 

 individual adaptation plays a most prominent part. 



Who has not marvelled at the fidelity and accuracy 

 of the information which our senses convey to us from 

 the surrounding world, more especially those of the far- 

 reaching eye ? The information so gained furnishes the 

 premisses for the conclusions which we come to, the acts 

 that we perform ; and unless our senses convey to us 

 correct impressions, we cannot expect to act accurately, 

 so that results shall correspond with our expectations. 

 By the success or failure of our acts we again and again 

 test the truth of the information with which our senses 

 supply us, and experience, after millions of repetitions, 

 shows us that this fidelity is exceedingly great, in fact, 

 almost free from exceptions. At all events, these exceptions, 

 the so-called illusions of the senses, are rare, and are only 

 brought about by very special and unusual circumstances. 



Whenever we stretch forth the hand to lay hold of 

 something, or advance the foot to step upon some object, 

 we must first form an accurate optical image of the position 

 of the object to be touched, its form, distance, &c., or we 

 shall fail. The certainty and accuracy of our perception 

 by the senses must at least equal the certainty and 

 accuracy which our actions have attained after long 

 practice ; and the belief, therefore, in the trustworthiness 

 of our senses is no blind belief, but one, the accuracy of 

 which has been tested and verified again and again by 

 numberless experiments. 



Were this harmony between the perceptions through 

 the senses and the objects causing them, in other words, 

 this basis of all our knowledge, a direct product of the 

 vital principle, its formative power would, in fact, then 

 have attained the highest degree of perfection. But an 



