OBSERVATION AND EXPERIMENT. 



249 



position of the planets ; because ex- 

 perience has shown, as a very super- 

 ficial experience is sufficient to show, 

 that in such cases that circumstance 

 is not material to the result : and 

 accordingly, in the ages when men 

 believed in the occult influences of 

 the heavenly bodies, it might have 

 been unphilosophical to omit ascer- 

 taining the precise condition of those 

 bodies at the moment of the experi- 

 ment. As to the degree of minute- 

 ness of the mental subdivision, if we 

 were obliged to break down what we 

 observe into its very simplest elements, 

 that is, literally into single facts, it 

 would be difficult to say where we 

 should find them : we can hardly 

 ever affirm that our divisions of any 

 kind have reached the ultimate unit. 

 But this, too, is fortunately unneces- 

 sary. The only object of the mental 

 separation is to suggest the requisite 

 physical separation, so that we may 

 either accomplish it ourselves, or seek 

 for it in nature ; and we have done 

 enough when we have carried the 

 subdivision as far as the point at 

 which we are able to see what obser- 

 vations or experiments we require. 

 It is only essential, at whatever point 

 our mental decomposition of facts may 

 for the present have stopped, that we 

 should hold ourselves ready and able 

 to carry it farther as occasion requires, 

 and should not allow the freedom of 

 our discriminating faculty to be im- 

 prisoned by the swathes and bands of 

 ordinary classification, as was the case 

 with all early speculative inquirers, 

 not excepting the Greeks, to whom it 

 seldom occurred that what was called 

 by one abstract name might, in reality, 

 be several phenomena, or that there 

 was a possibility of decomposing the 

 facts of the universe into any ele- 

 ments but those which ordinary lan- 

 guage already recognised. 



§ 2. The different antecedents and 

 consequents being, then, supposed to 

 be, so far as the case requires, ascer- 

 tained and discriminated from one 

 another, we are to inquire which is 



connected with which. In every in- 

 stance which comes under our obser- 

 vation, there are many antecedents 

 and many consequents. If those 

 antecedents could not be severed 

 from one another except in thought, 

 or if those consequents never were 

 found apart, it would be impossible 

 for us to distinguish (d posteriori at 

 least) the real laws, or to assign to 

 any cause its effect, or to any effect 

 its cause. To do so, we must be able 

 to meet with some of the antecedents 

 apart from the rest, and observe what 

 follows from them ; or some of the 

 consequents, and observe by what they 

 are preceded. We must, in short, fol- 

 low the Baconian rule of varying the 

 circumstances. This is, indeed, only 

 the first rule of physical inquiry, and 

 not, as some have thought, the sole rule; 

 but it is the foundation of all the rest. 

 For the purpose of varying the cir- 

 cumstances, we may have recourse 

 (according to a distinction commonly 

 made) either to observation or to ex- 

 periment ; we may either Jind an 

 instance in nature suited to our pur- 

 poses, or, by an artificial arrangement 

 of circumstances, viake one. The 

 value of the instance depends on 

 what it is in itself, not on the mode 

 in which it is obtained : its employ- 

 ment for the purposes of induction 

 depends on the same principles in the 

 one case and in the other, as the 

 uses of money are the same whether 

 it is inherited or acquired. There is, 

 in short, no difference in kind, no 

 real logical distinction, between the 

 two processes of investigation. There 

 are, however, practical distinctions to 

 which it is of considerable import- 

 ance to advert. 



§ 3. The first and most obvious 

 distinction between Observation and 

 Experiment is, that the latter is an 

 immense extension of the former. It 

 not only enables us to produce a much 

 greater number of variations in the 

 circumstances than nature spontane- 

 ously offers, but, also, in thousands of 

 cases, to produce the precise sort of 



