24 THE POPULAR SCIENCE MONTHLY. 



the object whose image passes over his eye is in motion. It is thus 

 that when a person has come to us habitually at a certain hour, say 

 the postman to deliver our letters, we may readily take some other 

 person who appears at the time for him, and be ready to affirm or to 

 swear that we saw him. It is thus that " the wish is father to the 

 thought ; " that is, we are inclined to believe what we wish and ex- 

 pect. It is thus, too, that in times of excitement, personal, political, 

 and religious, we readily fall in with the fancies created by our fears 

 and our hopes. Not only so, but a vivid idea reaching down from the 

 brain may produce the same effect on the sensorium as the external 

 object does through the sense of sight or hearing. Dr. Carpenter 

 has seized an important truth in explaining in this way the erroneous 

 declarations given by honest enough persons believing in mesmerism 

 and spirit-rapping, and ever seeking for signs and wonders. He is 

 right, too, in explaining how strong religious feelings may raise illu- 

 sory expectations and beliefs, and that the testimony given by per- 

 sons under their influence may be partial or valueless. 



I think I discover proof that even scientific men may fall under 

 the influence of this " prepossession " and " expectancy." I see an 

 example of it in the way in which many of them account for our 

 thoughts and resolutions : they call them reflex action. The discovery 

 of the nature of automatic motion was one of the most important dis- 

 coveries of the last age. An action goes along a nerve to the centre 

 of a ganglion, and comes out in motion by another nerve: thus, if a 

 frog's foot is pricked, it is immediately drawn in. Of much the same 

 kind is the reflex action of the sensori-motor system. My nostrils are 

 affected by a pungent substance, the action goes on to the sensorium, 

 and a sneeze is the result. So far we have a well-understood process. 

 But can we go on to explain in this way our special mental acts ? The 

 language used by some physiologists is fitted to leave the impression 

 that all mental action is the reflex of some action from without, proba- 

 bly a sensation. Let us look at a case. I receive a letter informing 

 me that a friend at a distance is in deep distress, needs me to defend 

 him by my presence, my purse, and my counsel, against a false accu- 

 sation, and I hasten to his assistance. Is all this merely a reflex ac- 

 tion called forth by the appeal in the letter ? Let us carefully inquire 

 how much and how little physiology can explain. It can show how 

 the writing in the letter, after passing through the eye, is reflected on 

 the retina, thence carried through the optic nerve to the sensorium, 

 thence it may be transmitted to the gray matter at the periphery of 

 the brain, and produce there, it may be, some motion or new ar- 

 rangement of the cells. But it can go no farther. When I under- 

 stand the letter, when I comprehend the position of my friend, when 

 I conclude that the accusation against him is false, when I feel that I 

 ought to assist him, and for this purpose travel a long way and make 

 many sacrifices, we have come to processes that cannot be explained 



