194 w. JAMES :

reach of his hands. But the geometrical relations here spoken of are nothing but identities recognised between the directions and sizes perceived in this way and those of our ordinary space-world. The two worlds do not fit each other intuitively. How lax the connexion between the system of visual and the system of tactile directions is in man, appears from the facility with which microscopists learn to reverse the move- ments of their hand in manipulating things on the stage of the instrument. To move the slide to the seen left they must draw it to the felt right. But in a very few days the habit becomes a second nature. So in tying our cravat, shaving before a mirror, &c., the right and left sides are inverted and the directions of our hand movements are the opposite of what they seem. Yet this never annoys us. Only when by accident we try to tie the cravat of another person do we learn that there are two ways of combining sight and touch perceptions. Let any one try for the first time to write or draw while looking at the image of his hand and paper in a mirror, and he will be utterly bewildered. But a very short training will teach him to undo in this re- spect the associations of his previous lifetime. Prisms show this in an even more striking way. If the eyes be armed with spectacles containing slightly prismatic glasses with their bases turned, for example, towards the right, every object looked at will be apparently translocated to the left ; and the hand put forth to grasp any such object will make the mistake of passing beyond it on the left side. But less than an hour of practice in wearing such spectacles rectifies the judgment so that no more mistakes are made. In fact the new-formed associations are already so strong that when the prisms are first laid aside again the opposite error is committed, the habits of a lifetime violated, and the hand now passed to the right of every object it seeks to touch. 1 1 It might, indeed, seem incredible that life-long association should be so rapidly undone. Were there any truth at all in the prevalent modern doctrine that ancestral habits engender fixed instincts in the progeny, one would say that the connexion with each other of the space-directions given by different senses ought to be congenital, inseparable and unconquerable. The facts cited might be taken to show that this modern doctrine, how- ever it may be verified for lower forms, fails in its application to man. It must be remembered, however, that the association of particular body- movement directions with particular visual directions is not so constant as the objection assumes, even in creatures ignorant of mirrors, prisms and lenses. Every time we move one end of a lever towards the right we see the other end move towards the left. Every time we pull down a rope or