74 LAY SERMONS, ESSAYS, AND REVIEWS. [v. 



of the current, which returned by and by to its original 

 direction. 



I have myself timed the heart of these little animals. I found 

 it as regular as possible in its periods of reversal : and I know 

 no spectacle in the animal kingdom more wonderful than that 

 which it presents all the more wonderful that to this day it 

 remains an unique fact, peculiar to this class among the whole 

 animated world. At the same time I know of no more striking 

 case of the necessity of the verification of even those deductions 

 which seem founded on the widest and safest inductions. 



Such are the methods of Biology methods which are ob 

 viously identical with those of all other sciences, and therefore 

 wholly incompetent to form the ground of any distinction 

 between it and them. 1 



But I shall be asked at once, Do you mean to say that there 

 is no difference between the habit of mind of a mathematician 

 and that of a naturalist ? Do you imagine that Laplace might 

 have been put into the Jardin des Plantes, and Cuvier into the 

 Observatory, with equal advantage to the progress of the 

 sciences they professed ? 



To which I would reply, that nothing could be further from 

 my thoughts. But different habits and various special ten 

 dencies of two sciences do not imply different methods. The 

 mountaineer and the man of the plains have very different 

 habits of progression, and each would be at a loss in the other s 

 place ; but the method of progression, by putting one leg before 

 the other, is the same in each case. Every step of each is a 

 combination of a lift and a push ; but the mountaineer lifts 

 more and the lowlander pushes more. And I think the case of 

 two sciences resembles this. 



I do not question for a moment, that while the Mathema 

 tician is busy with deductions from general propositions, the 

 Biologist is more especially occupied with observation, compari 

 son, and those processes which lead to general propositions. All 



1 Save for the pleasure of doing so, I need hardly point out my obligations 

 to Mr. J. S. Mill s &quot; System of Logic,&quot; in this view of scientific method. 



