50 Mi; I HOD OF DISCOVERY 



p-a vit.it ion. The method by which men of science establish 



nee of that law is exactly the same as that by 



we have established the trivial proposition about 



iturness of hard and green apples. But we believe 



it in Mieh an extensive, thorough, and unhesitating manner 



>e the universal experience of mankind verifies it, 



and we can verify it ourselves at any time ; and that is 



the strongest possible foundation on which any natural 



law can rest. 



So much by way of proof that the method of establishing 

 laws in science is exactly the same as that pursued in 

 common life. Let us now turn to another matter (though 

 really it is but another phase of the same question), and 

 that is, the method by which, from the relations of certain 

 phenomena, we prove that some stand in the position of 

 causes towards the others. 



I want to put the case clearly before you, and I will 

 therefore show you what I mean by another familiar 

 example. I will suppose that one of you, on coming 

 down in the morning to the parlour of your house, finds 

 that a tea-pot and some spoons which had been left in the 

 room on the previous evening are gone, the window is 

 open, and you observe the mark of a dirty hand on the 

 window-frame, and perhaps, in addition to that, you 

 notice the impress of a hob-nailed shoe on the gravel 

 outside. All these phenomena have struck your attention 

 instantly, and before two minutes have passed you say, 

 " Oh, somebody has broken open the window, entered 

 the room, and run off with the spoons and the tea-pot ! " 

 That speech is out of your mouth in a moment. And 

 you will probably add, " I know there has ; I am quite 

 sure of it 1 " You mean to say exactly what you know ; 

 but in reality what you have said has been the expression 

 of what is, in all essential particulars, an Hypothesis. 

 lo not know it at all ; it is nothing but an hypothesis 

 rapidly framed in your own mind ! And it is an hypothesis 

 founded on a long train of inductions and deductions. 



What are those inductions and deductions, and how 

 you got at this hypothesis ? You have observed, 

 in the first place, that the window is open; but by a 

 ning involving many Inductions and Deduc- 

 tions, you have probably arrived long before at the General 

 and a very good one it is that windows do not 

 open of themselves ; and you therefore conclude that 



