LAW; — ITS DEFINITIONS. IOI 



It is the very certainty and invariableness of the 

 laws of Nature which alone enables us to use 

 them, and to yoke them to our service. 



Now, the laws of Nature are employed in 

 the system of Nature in a manner precisely 

 analogous to that in which we ourselves em- 

 ploy them. The difficulties and obstructions 

 which are presented by one law in the way of 

 accomplishing a given purpose, are met and 

 overcome exactly on the same principle on 

 which they are met and overcome by Man — viz., 

 by knowledge of other laws, and by resource in 

 applying them, — that is, by ingenuity in mechani- 

 cal contrivance. It cannot be too much insisted 

 on, that this is a conclusion of pure Science. The 

 relation which an organic structure bears to its 

 purpose in Nature can be recognised as certainly 

 as the same relation between a machine and its 

 purpose in human art. It is absurd to maintain, 

 for example, that the purpose of the cellular 

 arrangement of material in combining lightness 

 with strength, is a purpose legitimately cognisable 

 by Science in the Menai Bridge, but is not as 

 legitimately cognisable when it is seen in Nature, 



