THE SCOPE OF PHILOSOPHY 



presentation 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 cus- 

 tomary 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 astronomer 

 has linked indissolubly in his mind the phe- 

 nomena 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 irregular- 

 ities of motion. When, therefore, in the instance 

 before him, after calculating the resultant of all 

 the known forces in operation, he finds a re- 

 siduum of motion which is unaccounted 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 exist- 

 ence of planetary matter other than the plane- 

 tary 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 mo- 

 tion, the size, distance, and orbit of the unknown 

 planet. Nothing can better illustrate the state- 

 ment that scientific and ordinary knowledge are 



51 



