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The definitions which are usually attached to the word have been 

 well stated as follows: — "(r) Speculation — a doctrine which termi- 

 nates in speculation or contemplation without a view to practice. 

 Here it is taken in an unfavourable sense as implying something 

 visionary. (2) An exposition of the general principles of any 

 science, as the theory of music. (3) The science distinguished 

 from the art — for example, the theory of medicine as distinguished 

 from the practice. (4) The philosophical explanation of phe- 

 nomena, either physical or moral, as Lavoisier's theory of 

 combustion, Smith's theory of moral sentiments." 



Theory is distinguished from hypothesis, a word very often 

 used synonymously, thus : — " A theory is founded on inferences 

 drawn from principles which have been estahlisJied on independent 

 evidence; a hypothesis is a proposition assumed to account for 

 certain phenomena, which has no other evidence of truth than that it 

 affords a satisfcactory explanation of those phenomena." 



Mr. Kendall seems to have somewhat mistaken the true 

 meaning of the word. He makes the term theory to a great extent 

 answer to fact, from which it appears to have a meaning entirely 

 different. Theory is defined by him as follows : — " A theory then 

 in physical science is an explanation of natural phenomena founded 

 on facts known to be true, from evidence independent of those 

 phenomena or appearances;" and he goes on to argue that a 

 theory must be a fact, while he has in this definition affirmed that 

 it is "an explanation founded on facts." If he had said, "a theory 

 is an explanation founded on i/ferences drawn from facts established 

 on independent evidence," no difficulty would arise in accepting 

 the proposition, as it bears upon physical science ; but it can 

 hardly be assumed, for instance, that the explanation of the rise of 

 a column of water in a tube from which the air has been exhausted 

 is an "inference drawn from facts," it is rather a statement of facts 

 themselves, and of their bearing one upon another. Each of the 

 steps in the process is known and can be explained up to the 

 highest point to which explanation is possible in the present state 

 of knowledge. Not so with regard, for instance, to the atomic 

 theory or the theory of gravitation. These are not and have not 



