I 9 4 THE SCIENCE OF LOGIC 



we can infer that there must be, connected with the whole 

 event, something that causes d ; and we can then proceed to 

 search for this something in the surroundings of the event. No 

 doubt, our knowledge of a complex event is rarely so perfect as 

 this symbolism implies ; the latter represents rather an ideal. But 

 it expresses the sort of consideration embodied in the Method of 

 Residues. It shows us, too, that the analysis here effected is 

 mental rather than actual, and that deductive inference from our 

 previous knowledge is the predominant feature of this analysis. 



We may now state the rule or canon which is the ground of 

 the analysis. It is formulated by Mill in this way : 



&quot; SUBDUCT FROM ANY PHENOMENON SUCH PART AS is KNOWN 



BY PREVIOUS INDUCTIONS TO BE THE EFFECT OF CERTAIN ANTE 

 CEDENTS, AND THE RESIDUE OF THE PHENOMENON IS THE EFFECT 

 OF THE REMAINING ANTECEDENTS.&quot; 



It is stated more briefly, thus, by Mr. Joseph: 1 &quot;Nothing 

 is the cause of one phenomenon which is known to be the cause of a 

 different phenomenon.&quot; To suit cases where no antecedent is forth 

 coming, within the ambit of the complex event itself, for an un 

 explained residue, Dr. Mellone 2 formulates the following rule, 

 which becomes, in such cases, a &quot;finger-post to the unexplained&quot; : 

 &quot; When any part of a complex phenomenon is still unexplained by 

 the causes which have been assigned, a further cause for this re 

 mainder must be sought &quot;. 



The method can be applied both to experimental cases and 

 to cases of simple observation. As applied to the former it is a 

 quantitative method, its value depending on the degree of exact 

 ness with which we can make use of measurement. It is ex 

 tensively applied in this way to experiments in chemical analysis. 

 The following example, from Jevons Elementary Lessons in Logic* 

 will illustrate the use of it. &quot; Thus, the composition of water 

 is ascertained by taking a known weight of oxide of copper 

 [C], passing hydrogen [H] over it in a heated tube [T 1 ] and con 

 densing the water [IV] produced in a tube [7^ 2 J containing sul 

 phuric acid [in known weight, S]. If we subtract the original 



l op. cit., p. 404. His formula emphasizes the fact that reciprocating causes 

 only are in contemplation. The author formulates (ibid, n.) other grounds of elimin 

 ation applicable to causes that are non-reciprocating either because they contain too 

 little (partial causes, sine qua conditions), or too much, for the effect. These are 

 eminently instructive, e.g. that from Hume s Treatise, etc., pt. III., xv. &quot; Where 

 several different objects produce the same effect, it must be by means of some quality, 

 which we discover to be common amongst them &quot;. 



o/. cit., p. 3x5. 3 P- 254. 



