446 ACTUAL WORKING IN ORIGINAL RESEARCH. 



ness is largely a fortuitous result of independent trains of 

 conditions. As causes and their effects are indissolubly 

 connected together, separable effects are usually produced 

 by separable causes, and inseparable ones by the same 

 cause ; for instance, the various effects of heat produced 

 simultaneously in a piece of metal are mostly inseparable. 

 Two coincident circumstances may be inseparable because 

 they are produced by the same force or agent ; such phe- 

 nomena, if they follow different rates of variation, must 

 be separately investigated. By allowing only one cause 

 to operate in a given case, we know that any two phenomena 

 or effects which then occur must be related to each other, 

 either as an intermediate cause and its effects, Or as a ne- 

 cessary condition and effect, or as coincident effects of the 

 original cause. 



Separable coincidences, after having been proved to 

 be such by being excluded by experiment, need not be 

 further considered ; we must not, however, assume either 

 separable or inseparable circumstances to be mere coinci- 

 dences without proving them to be such. Inseparable 

 circumstances can only be proved to be coincidences by 

 indirect means, i.e. by showing that they cannot be any- 

 thing else ; and this is usually done by fully accounting 

 for the effect by the other causes and conditions present, 

 and thus showing them to be unnecessary ; the determina- 

 tion of inseparable coincidences, therefore, is one of the 

 last steps in an experimental research. We find causes 

 and necessary conditions before we find inseparable coinci- 

 dent circumstances. An inseparable coincidence may be 

 distinguished both from a cause and from a necessary 

 static condition by its not being indispensable to the 

 effect nor contributing to it. 1 That which appears to 



1 Respecting fortuitous circumstances, see Jevons's Principles of 

 Science, vol. i. p. 302. 



