458 SPECIAL METHODS OF DISCOVERY. 



special system of rules of discovery on a comparatively 

 limited scale in that subject ; and an inductive system for 

 science in general consists of a somewhat similar but more 

 extensive method, applicable to all the simple sciences of 

 matter and energy. 



As the only two agents concerned in scientific discovery 

 are external nature and the human faculties, the nature of 

 a discovery depends essentially upon two things, viz., first 

 and most essentially, upon the kind of phenomenon pre- 

 sented to us ; and, second, upon the kind of aspect in 

 which we perceive it. Out of these two conditions arise what 

 for the sake of convenience I will venture to call the fun- 

 damental laws of scientific discovery, viz., 1 . that of disco- 

 very by means of experiments or natural phenomena ; and, 

 2. that of discovery by means of the senses and intellect. 

 The chief law of discovery by means of natural phenomena 

 is, that every new substance or force, and every new com- 

 bination of matter or its forces, produces new effects, 

 except in cases where there are preventive conditions ; and, 

 conversely, every new effect may be produced either by a 

 new substance or by a new arrangement of matter or its 

 forces. In most instances, therefore, in which a new dis- 

 covery is made, we observe for the first time either the 

 effect of a new substance or of a new disposition of the 

 forces and substances of nature ; or a new cause, i.e. 

 a new substance, or a new arrangement of matter and its 

 forces, which produced the particular effect. The chief 

 law of discovery by means of the senses and intellect is, 

 that whenever we perceive or compare any truth or class 

 of truths in a new aspect, we obtain new knowledge ; 

 and therefore, also, whenever a truth or class of truths is 

 presented to us in a new aspect, we make a new discovery. 

 When we perceive, compare, or reason upon a phenomenon 

 in a new aspect, we evolve new truths respecting it : thus, 



