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to succeed in his practice, other things of course being the same. 

 The former in using a siphon on the top of a high mountain would 

 be misled by the knowledge he had gained by observation near the 

 sea level. But the latter could not, because he would know 

 theoretically that the higher he ascends above the level of the sea 

 the less is the pressure of the air, and therefore the less will be the 

 rise of a column of water in an exhausted tube. 



Further on Mr. Kitchin remarks " that a theory must needs 

 be abandoned if in practice it is found untenable." I should rather 

 say so, if your practice is perfect before you abandon any theory. 



I agree with Mr. Nixon in his criticism of Mr. Kitchin's 

 remarks on the atomic theory — so called. The only value that I 

 can see in the theory is that which attaches to every opinion — in 

 which there is any appearance of truth — ^that it stimulates to 

 further inquiry. To say that the whole practice of modern 

 chemistry hinges upon it, seems to me like putting the cart before 

 the horse. 



From Mr. Kitchin's remarks on the nebular hypothesis and 

 Darwin's theory of evolution — which he apparently sets on the 

 same level of probability — he seems to make no distinction between 

 hypothesis and theory, notwithstanding his definitions wherein he 

 makes considerable difference between them. We know that 

 Laplace, in his explanation of the planetary system, begins with a 

 nebulous cloud — which he assumes — and out of that cloud evolves, in 

 the most satisfactory manner, the whole planetary system. But given 

 the planets as they are now, with their motions of rotation and 

 translation, neither Laplace nor any of his followers have been able, 

 by any process of deduction at present kno\%'n, to arrive at the 

 conclusion that those planets originally existed as a nebulous cloud. 

 It is clear, therefore, that his explanation is founded on an assump- 

 tion — the same as Dalton's atomic theory. Now, Darwin's theory 

 is entirely different. It is foumded on facts. He begins with the 

 facts that both plants and animals vary, and that there is constantly 

 going on between them a struggle for existence. From these 

 facts he infers, in the most logical manner, that species may be 

 modified indefinitely. There is, therefore, this diffsrnce bstwee 



