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LETTERS ON TREES. 



perceive in the facts that have passed under our view, 

 one common principle running through and connecting 

 them all, one general fact embracing and expressive 

 of them all. 



2. If so, I would wish to lead you one short step 

 farther. If my theory be a sound one, it is the 

 expression of a Law of Nature ; if our inquiries have 

 brought us within the view of a general fact or common 

 principle, including and explaining a number of indi- 

 vidual, and, in themselves, solitary phenomena, they 

 have brought us within the view and to the grasp of a 

 Law of Nature. 



3. But what is a Law of Nature ? To say that it 

 is the expression of an ultimate fact in nature, of which 

 no other account can be given than that it depends on 

 the will of the Author of Nature to say that " Laws 

 of Nature are nothing else but the most general facts 

 relating to the operations of Nature, which include a 

 great many particular facts under them,"f is, it seems 

 to me, a definition which convevs but half the truth — 

 nay, which by its negative form obscures it altogether. 

 We may, I think, rise a step higher than this, and, 

 defining it positively, say with Plato, that a Law of 

 Nature is the expression of an idea in the divine 

 mind — the manifestation of a plan or purpose in the 

 mind of the Creator. To discover a Law of Nature is 



* Alison, Outlines of Physiology, 3d Ed. p. 8. 



t Reid's Inquiry into the Human Mind, chap. vi. § 13. 



