PHILOSOPHY OF INDUCTIVE INFERENCE. 253 



the diameter of a circle, with its apex upon the circum- 

 ference, apparently contains a right angle, we may 

 ascertain that all triangles in similar circumstances will 

 contain right angles. This is a case of pure space reason- 

 ing, apart from circumstances of time or quality, and it 

 seems to be governed by different principles of reasoning. 

 I shall endeavour to show, however, that geometrical 

 reasoning differs but in degree from that .which applies 

 to other natural relations. If we observe that the com- 

 ponents of a binary star have moved for a length of time 

 in elliptic curves, we have reason to believe that they will 

 continue so to move. Time and space relations are here 

 complicated together. 



The Relation of Cause and Effect. 



In a very large part of the scientific investigations 

 which must be considered, we deal with events which 

 follow from previous events, or with existences which 

 succeed existences. Science, indeed, might arise even were 

 material nature a fixed and changeless whole. Endow 

 mind with the power to travel about, and compare part 

 with part, and it could certainly draw inferences concern- 

 ing the similarity of forms, the co-existence of qualities, 

 or the preponderance of a particular kind of matter in 

 a changeless world. A solid universe, in at least approxi- 

 mate equilibrium, is not inconceivable, and then the rela- 

 tion of cause and effect would evidently be no more than 

 the relation of before and after. As nature exists, how- 

 ever, it is a progressive existence, ever moving and 

 changing as time, the great independent variable, pro- 

 ceeds. Hence it arises that we must continually compare 

 what is happening now with what happened a moment 

 before, and a moment before hat moment, and so on, 

 until we reach indefinite periods of past time. A comet 



