SO On Some Processes of Scientific Reasoning. 



Chemistry is almost entirely based on Ideal construction. 

 We popularly employ the term "gold" to denote various 

 objects which possess certain properties of weight, color, &c, 

 but the gold of the chemist is an ideal conception bearing the 

 same relation to real gold as a geometrical sphere does to a 

 real sphere ; in fact, I believe I am correct in saying that 

 no chemical element or definite chemical compound exists in 

 nature, or can be produced artificially, in a state of absolute 

 purity. The law of chemical combination in definite propor- 

 tions is not accurately true for real substances, although in 

 many experiments the deviation from the law is practically 

 insensible. The same is true of the relation between the 

 combining equivalent and specific heat of a gas, and, in 

 short, of all numerical chemical laws. 



Chemical affinity is a conception which is at present of an 

 entirely metempirical nature. The phenomena of chemical 

 composition and decompositions cannot be explained by the 

 laws of ordinary physics, and it is convenient to assume an 

 " unknown something," called Chemical Affinity, as the cause 

 of these phenomena. Chemical Affinity is sometimes used in 

 another sense, as a name for the peculiar relations between 

 phenomena which it is in its other meaning the cause of — 

 an unfortunate ambiguity — but the word has many com- 

 panions in misfortune. 



I may here allude to the fact that the separation of the 

 different branches of Science from each other is purely an 

 artificial one. All the relations between real material sub- 

 stances are complicated relations, involving dynamical, 

 thermal, electrical, and, probably, chemical phenomena ; 

 and the perfect solution of the simplest mechanical problem 

 would involve the application of all the Sciences which 

 respectively deal with these phenomena. It is only by 

 adopting the method of Ideal Construction that the different 

 Inorganic Sciences can be separated from one another. 



Passing now from inorganic to organic phenomena, in the 

 Ideal Vertebral Skeleton of Owen we have a capital example 

 of Ideal Construction. However, Biology has at present 

 scarcely reached the deductive stage, and until it has 

 become, to some considerable extent, a Deductive Science, 

 it cannot be expected to illustrate the full value of that 

 method of reasoning. 



In Biology, we have the introduction of a metempirical 

 element, which has been the cause of very violent contro- 

 versy; — I refer to the idea of Life, Vitality, or Vital Force, 



