REASON. 321 



parison. The inference is formed out of the perception, as it 

 were, immediately, and does not require to pass through any 

 such process of reflection as the term ratiocination is apt, and 

 indeed ought, to imply ; the ratios at this stage are perceived, 

 compared, and the inference from them drawn, without the 

 need of deliberate thought. For instance, I am hurrying to 

 catch a train, and meet a man in the street hurrying in the 

 opposite direction ; we both begin rapidly to dance from side 

 to side in our endeavour to pass one another, and each time 

 we do so it is evident that we have each inferred that the 

 other will pass on the opposite side : yet these successive acts 

 of inference are made with such rapidity, that not only has 

 there been no deliberate thought in the matter, but it is only 

 by such thought that I can afterwards find that I must have 

 performed so many separate acts of inference. 



Clearly, then, it is in these lower stages of perception 

 that we have to look for the first germ of reason : for this 

 purpose, let us first interrogate our own perceptions. The 

 large measure in which inference enters into the very struc- 

 ture even of our most habitual perceptions is easily shown. 

 Sir David Brewster has noticed the fact, which must have 

 been observed by every one, that when looking through a 

 window on the pane of which there is a fly or a gnat, if the 

 eyes are adjusted for a greater distance, so that the gnat is 

 not clearly focussed, the mind at once infers that it is a bird, 

 or some other much larger object seen at a greater distance.* 

 Now this shows that in the case of all our visual perceptions 

 mental inference is perpetually at work, compensating for the 

 effects of distance in diminishing apparent size. No less 

 constant must be the work of mental inference in compen- 

 sating for the eilects of the "blind spot" upon the retina. 

 For if the vision be directed to a coloured surface, the part of 

 the surface, which, on account of the blind spot, is not really 

 Been, yet appears to In; seen ; and not only so, hut it appeal ! 

 to be coloured the same tint as the rest of the surface, what- 

 ever this may happen to be: unconscious inference supplies 

 the colour. .Mr. .Sully has devoted a large part of his work 

 on " Illusions" to a survey and classifical ion of " The Illusions 

 of Perception ;" and in most of the instances which he gives 

 it is apparent, as he observes, that the illusion arises through 

 the mental "application of a rule, valid for the majority of 



• Litters on Natural Magic, VII. 



