444 ACTUAL WORKING IN OKIGINAL RESEARCH. 



one may be distinguished by its introduction (all othei 

 conditions remaining^the same) being attended by a total 

 cessation of the effect. 



In the discovery of static conditions, as well as in that 

 of dynamic causes, we often meet with circumstances 

 which cannot be altered or removed at all, and others 

 which can only be altered by changing several at the same 

 time ; in each of these cases we proceed as in the dis- 

 covery of causes. 



CHAPTEK XL VIII. 



DISCOVERT OF COINCIDENCES. 



BEFORE we can completely explain a phenomenon we 

 require not only to find its true cause, its chief relations 

 to other causes, and all the conditions which determine 

 how the cause operates, and what its effect and amount 

 of effect are, but also all the coincidences. Before we 

 can determine the cause of an effect, we usually require 

 to know what are the coincidences. By a coincidence is 

 meant any circumstance which, although occurring with 

 or immediately before a phenomenon, is not at all neces- 

 sary to its production or existence ; for example, gold is 

 heavy and yellow, but its yellowness is not a cause or an 

 essential condition of its heaviness, although usually oc- 

 curring with it. Darkness also invariably precedes, and a 

 somewhat higher temperature usually accompanies, day- 

 light ; but neither is a cause or a necessary condition of 

 it, for we know that the relative position of the sun to a 

 particular part of the earth is the cause of each. A coin- 

 cidence is an independent circumstance. 



All the immediate conditions of an effect are concomi- 



