a. ii.] THE SCOPE OF PHILOSOPHY. 35 



relations of likeness and unlikeness which science detects 

 and classifies. The child who, when an orange is presented 

 to him, infers that on sucking it he shall experience a 

 pleasant taste; the savage who, finding the half-eaten 

 carcass of a sheep, concludes that a lion has been in the 

 neighbourhood; and Leverrier, who, noticing that the ob- 

 served motions of Uranus do not coincide with its motions 

 as predicted, suspects the existence of a still remoter planet 

 which disturbs it — go, all of them, through what is essen- 

 tially the same process. The child has mentally grouped 

 together the attributes of an orange ; and when certain 

 members of the group — as the shape and colour are after- 

 wards presented to his consciousness, there occurs a mental 

 representation of the remaining member — the agreeable 

 taste. The savage, from direct or hearsay experience, has 

 grouped together many cases of the eating of sheep by lions, 

 and from the presence of a certain number of the customary 

 phenomena, he classifies this new case with his already- 

 formed group of cases ; he assigns for the phenomenon a 

 cause like the causes which he has known. The astro- 

 uomer has linked indissolubly in his mind the phenomena 

 of celestial motions with the phenomena of gravitative force, 

 and has grouped many cases in which such force, brought to 

 bear on a planet from different quarters, causes irregularities 

 of motion. When, therefore, in the instance before him, 

 after calculating the resultant of all the known forces in 

 operation, he finds a residuum of motion which is unac- 

 counted for, what does he do ? He infers a like force as the 

 cause of the residuary motion ; and since there is no force 

 without, matter, he infers the existence of planetary matter 

 other than the planetary matter already taken into account. 

 He enlarges his group of cases in which planets perturb each 

 other's courses, by admitting a hypothetical like case ; and 

 forthwith proceeds to calculate, from the amount of residuary 

 motion, the size, distance, and orbit of the unknown planet 



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