REMAINING LAWS OF NATURE. 141 



which affirm the bare fact of existence, they have a peculiarity 

 which renders the logical treatment of them a very easy 

 matter ; they are generalizations which are sufficiently proved 

 by a single instance. That ghosts, or unicorns, or sea- 

 serpents exist, would be fully established if it could be ascer 

 tained positively that such things had been even once seen. 

 Whatever has once happened, is capable of happening again ; 

 the only question relates to the conditions under which it 

 happens. 



So far, therefore, as relates to simple existence, the 

 Inductive Logic has no knots to untie. And we may proceed 

 to the remaining two of the great classes into which facts 

 have been divided ; Resemblance, and Order in Space. 



2. Resemblance and its opposite, except in the case in 

 which they assume the names of Equality and Inequality, are 

 seldom regarded as subjects of science ; they are supposed to 

 be perceived by simple apprehension ; by merely applying our 

 senses or directing our attention to the two objects at once, or 

 in immediate succession. And this simultaneous, or virtually 

 simultaneous, application of our faculties to the two things 

 which are to be compared, does necessarily constitute the ulti 

 mate appeal, wherever such application is practicable. But, 

 in most cases, it is not practicable : the objects cannot be 

 brought so close together that the feeling of their resem 

 blance (at least a complete feeling of it) directly arises in the 

 mind. We can only compare each of them with some third 

 object, capable of being transported from one to the other. 

 And besides, even when the objects can be brought into im 

 mediate juxtaposition, their resemblance or difference is but 

 imperfectly known to us, unless we have compared them 

 minutely, part by part. Until this has been done, things in 

 reality very dissimilar often appear undistinguishably alike. 

 Two lines of very unequal length will appear about equal 

 when lying in different directions ; but place them parallel, 

 with their farther extremities even, and if we look at the 

 nearer extremities, their inequality becomes a matter of direct 

 perception. 



