IMPORTANCE OF QUALITATIVE TRUTHS. 203 



of everything, even of the great laws of consistency and 

 uniformity of nature. 



Qualitative truths of simple existence are the very 

 foundation of science, and the nearest approaching to 

 absolute of any truths we know. A qualitative truth is 

 not one of degree. In a qualitative sense, a thing must 

 either be or not be ; but a qualitative idea may be true or 

 untrue in all degrees from nothing to completeness. In 

 scientific discovery, whether in physics or chemistry, we 

 usually ascertain the existence of a thing, even though we 

 do not name it, before we determine its amount. The 

 methods of investigating the former are essentially logical, 

 and of the latter, both arithmetical and logical, be- 

 cause all mathematical reasoning must conform to logical 

 axioms. It is far more important to know the qualitative 

 fact of the mode or way in which transformation of phy- 

 sical energy is effected than even to know the quantitative 

 equivalent of that action. The discovery of a qualitative 

 fact leads to many questions respecting the quantitative 

 relations of that fact ; for instance, that of the existence 

 of thallium by Crookes, rubidium and caesium by Bun- 

 sen, of indium by Eeich and Eichter, and of gallium by 

 Boisbaudran, led to the questions, what was its atomic 

 weight, and in what proportions it combined with each of 

 the other elementary substances. The detection of dif- 

 ference or likeness of the thing discovered, by comparison 

 with things already known, is also largely dependent upon 

 qualitative knowledge. Every new discoverer must know 

 many qualitative truths, including all the physical and 

 chemical forces, their characteristics, chief properties and 

 relations ; all the elementary substances, and a great 

 number of their compounds, and the chief properties of all 

 these bodies, and of their actions upon each other. Newton, 

 Faraday, Volta, Oersted, Davy, Scheele, Priestley, Berzelius, 



