CONDITIONS OF SCIENTIFIC DISCOVERY. 463 



existence. Potassium, for example, does not explicitly 

 exist in nature, but is implicitly contained in its com- 

 pounds, and has been rendered explicit by discovery. 

 Numerous compounds also, not explicitly contained in 

 nature, have been rendered explicit by means of research. 



2. With regard to its dependence upon our mental 

 and physical faculties, it is evident that, as all our know- 

 ledge primarily arises from our experience, all existences 

 which lie beyond the reach of our senses and conscious- 

 ness, or which cannot be inferred from our sensory or con- 

 scious impressions by our intellectual powers, lie beyond 

 our powers of scientific discovery ; but those which do not 

 lie beyond the reach of our consciousness or intellect, or 

 their future developments, may be sooner or later dis- 

 covered by us. 



3. With respect to its dependence upon the kind of 

 discovery to be made, we know that whilst we cannot 

 make any discovery which is contradictory to the laws of 

 nature, we can so direct the use of our intellectual powers 

 as to be able to select, within a certain limit, the kind of 

 discovery we can make ; for instance, we can choose either 

 a physical or chemical subject of investigation, or a re- 

 search belonging to any one of the sciences. We know that 

 we can even so direct the use of our powers as to discover 

 a number of facts, a general truth, or even, to a certain 

 extent, a law or principle ; the latter, however, is by far 

 the most difficult and the most uncertain of success ; and 

 in each of these cases the special methods we employ are 

 somewhat different. The special methods employed in 

 making discoveries in physics differ to some extent from 

 those employed in chemistry ; they differ also in every 

 different science and branch of science. The discovery 

 also of laws .and principles requires a more extensive 

 method than that of finding ordinary facts ; and that of 



