TERMINOLOGY AND NOMENCLATURE. 279 



ciated immediately with the perception to which they 

 belong ; and not connected with it through the vague 

 usages of common language. The memory must 

 retain the sensation ; and the technical word must be 

 understood as directly as the most familiar word, and 

 more distinctly. When we find such terms as tin- 

 white or pinchbeck-brown, the metallic colour so 

 denoted ought to start up in our memory without 

 delay or search. 



" This, which it is most important to recollect with 

 respect to the simpler properties of bodies, as colour 

 and form, is no less true with respect to more com- 

 pound notions. In all cases the term is fixed to a 

 peculiar meaning by convention ; and the student, in 

 order to use the word, must be completely familiar 

 with the convention, so that he has no need to frame 

 conjectures from the word itself. Such conjectures 

 would always be insecure, and often erroneous. Thus 

 the term papilionaceous applied to a flower is employed 

 to indicate, not only a resemblance to a butterfly, but 

 a resemblance arising from five petals of a certain 

 peculiar shape and arrangement ; and even if the 

 resemblance were much stronger than it is in such 

 cases, yet if it were produced in a different way, as, 

 for example, by one petal, or two only, instead of a 

 1 standard/ two ' wings/ and a ' keel' consisting of 

 two parts more or less united into one, we should 

 no longer be justified in speaking of it as a ' papilio- 

 naceous* flower." 



When, however, the thing named is, as in this last 

 case, a combination of simple sensations, it is not 

 necessary in order to learn the meaning of the word, 

 that the student should refer back to the sensations 

 themselves; it may be communicated to him through 

 the medium of other words ; the terms, in short, may 



