418 THE PRINCIPLES OF SCIENCE. 



specially applicable to these brandies of science. Whatl 

 more I may be able to say upon the subject will be betteJ 

 said, if ever, when I arn able to take up the closelyJ 

 connected subject of Scientific Nomenclature, Terminology! 

 and Descriptive Representation. In the meantime, 1 havJ 

 wished to show, in a negative point of view, that natural 

 classification in the animal and vegetable kingdoms is a] 

 special problem, and that the special methods and difn-1 

 culties to which it gives rise are not those common to all 

 cases of classification, as so many physicists have supl 

 posed. Genealogical resemblances are only a special casej 

 of resemblances in general. 



Unique or Exceptional Objects. 



In framing a system of classification in almost an] 

 branch of science, we must expect to meet with unique 

 or peculiar objects, which are so called because they seei 

 to stand alone, having few analogies with other object 

 They may also be said to be sui generis, each unique ol 

 ject forming, as it were, a class by itself; or they ai 

 called nondescript, because in thus standing apart it 

 difficult to find terms in which to explain their properties 

 The rings of Saturn, for instance, form a unique obj&amp;lt; 

 among the celestial bodies. We have indeed considerec 

 this and many other instances of unique objects in th&amp;lt; 

 preceding chapter, on Exceptional Phenomena. Apparent 

 Singular, and Divergent Exceptions especially, are anak 

 gous in nature to unique objects. 



In the classification of the elements, Carbon stands 

 apart as a substance entirely unique in its powers o\ 

 producing compounds. It is considered to be a quadri 

 valent element, and it obevs all the ordinary laws 

 chemical combination. Yet it manifests powers of affinitj 

 in such an exalted degree that the substances in which 



