6 THE TONER LECTURES, 



only one-half of the power of sight, and objects then if seen are 

 seen in half. Suppose a man to be looked at, there would be 

 visible, if it is the left side of the brain which is affected, only 

 the right half of the bodj'. Wollaston himself had this trouble. 

 One day, trying to read the name of an instrument, the baro- 

 meter, he read " meter" only ; the other part of the word, 

 " baro," he could not see. Another eminent friend, while living 

 in France, Professor Agassiz, had the same affection. He saw 

 one-half of all objects. And a good many patients who are 

 affected especially with certain disorders of movement and with 

 diabetes have also this trouble ; they see but half of objects. 

 There are, therefore, cases which seem to be in favor of the 

 view. But, continuing to consider what ought to take place, we 

 find that, if the disease exists only in a small part of the left 

 side of the brain, in that portion which serves for sight, we 

 ought to find that then only one-half of one eye will be affected. 

 There are such cases. If it is the other part of that same half 

 of the base of the brain which is affected, then it is one-half of 

 vision in both eyes which should be affected. There are also 

 facts of this kind. 



There are, therefore, three kinds of facts which seem to sup- 

 port the view of Wollaston. But what of that ? Philosophers 

 do not accept conclusions because there are some facts which 

 support them. We accept conclusions when all the known 

 facts are either in perfect harmony or clearly prove the conclu- 

 sion ; and also when there is no fact that seems to be in oppo- 

 sition. It is requisite, therefore, either that all the facts are in 

 favor of the theory, or that while there are a number in favor 

 there are none in opposition. Such is not the case here. There 

 are a great many facts which show that a disease in one-half 

 of the brain will produce complete loss of sight of one eye, 

 either on the same or on the opposite side, or the two halves 

 of both eyes. Therefore there are three series of facts, while 



