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OPERATIONS SUBSIDIARY TO INDUCTION. 



concerning the laws of falling bodies 

 led to the question whether the pro- 

 per definition of a uniform force is 

 that it generates a velocity propor- 

 tional to the space from rest, or to the 

 time. The controversy of the vis viva 

 •was what was the proper definition 

 of the measure of force. A principal 

 (question in the classification of mine- 

 rals is, what is the definition of a 

 'mineral species? Physiologists have 

 endeavoured to throw light on their 

 subject by defining organisation, or 

 some similar term." Questions of the 

 same nature were long open, and are 

 not yet completely closed, i-especting 

 the definitions of Specific Heat, La- 

 tent Heat, Chemical Combination, 

 and Solution. 



"It is very important for us to 

 observe, that these controversies have 

 never been questions of insulated and 

 arbitrary definitions, as men seem 

 often tempted to imagine them to 

 have been. In all cases there is a 

 tacit assumption of some proposition 

 which is to be expressed by means of 

 the definition, and which gives it its 

 importance. The dispute concerning 

 the definition thus acquires a real 

 value, and becomes a question con- 

 cerning true and false. Thus in the 

 discussion of the question. What is 

 a uniform force? it was taken for 

 granted that gravity is a uniform 

 force. In the debate of the vis viva, 

 it was assumed that in the mutual 

 action of bodies the whole effect of 

 the force is unchanged. In the zoo- 

 logical definition of species, (that it 

 consists of individuals which have, or 

 may have, sprung from the same 

 parents,) it is presumed that indivi- 

 duals so related resemble each other 

 more than those which are excluded 

 by such a definition ; or, perhaps, 

 that species so defined have per- 

 manent and definite differences. A 

 definition of organisation, or of some 

 other term, which was not employed 

 to express some principle, would be 

 of no value. 



"The establishment, therefore, of 

 a right definition of a term, may 



be a useful step in the explication ot 

 our conceptions ; but this will be the 

 case then only when we have under 

 our consideration some proposition in 

 which the term is employed. Por 

 then the question really is, how the 

 conception shall be understood and 

 defined in order that the proposition 

 may be true. 



"To unfold our conceptions by 

 means of definitions has never been 

 serviceable to science, except when it 

 has been associated with an imme- 

 diate use of the definitions. The 

 endeavour to define a Uniform Force 

 was combined with the assertion that 

 gravity is a uniform force : the attempt 

 to define Accelerating Force was 

 immediately followed by the doctrine 

 that accelerating forces may be com- 

 pounded : the process of defining Mo- 

 mentum was connected with the prin- 

 ciple that momenta gained and lost 

 are equal : naturalists would have 

 given in vain the definition of Species 

 which we have quoted, if they had 

 not also given the characters of species 

 so separated. . . . Definition may be 

 the best mode of explaining our con- 

 ception, but that which alone makes 

 it worth while to explain it in any 

 mode, is the opportunity of using it 

 in the expression of truth. When a 

 definition is propounded to us as a 

 useful step in knowledge, we art; 

 always entitled to ask what principle 

 it serves to enunciate." 



In giving, then, an exact connota- 

 tion to the phrase, "a uniform force," 

 the condition was understood that 

 the phrase should continue to denote 

 gravity. The discussion, therefore, 

 respecting the definition resolved 

 itself into this question. What is there 

 of an uniform nature in the motions 

 produced by gravity? By observa- 

 tions and comparisons it was found, 

 that what was uniform in those mo- 

 tions was the ratio of the velocity 

 acquired to the time elapsed ; equal 

 velocities being added in equal times. 

 An uniform force, thei-efore, was 

 defined, a force wliich adds equal 

 velocities in equal times. So, again, 



