Page:Popular Science Monthly Volume 9.djvu/42

24 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 expect. 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 illusory expectations and beliefs, and that the testimony given by persons 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 discoveries 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, probably 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 accusation, and I hasten to his assistance. Is all this merely a reflex action 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 arrangement of the cells. But it can go no farther. When I understand 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