96 THE POPULAR SCIENCE MONTHLY. 



i 



of Ireland, knowing these facts and also the explanation of them which 

 Fresnel had given, thought about the subject, and he predicted that, 

 by looking through certain crystals in a particular direction,' we should 

 see not two dots, but a continuous circle. Mr. Lloyd made the experi- 

 ment, and saw the circle a result which had never been even sus- 

 pected. This has always been considered one of most signal instances 

 of scientific thought in the domain of physics. It is most distinctly an 

 application of experience, gained under certain circumstances, to entirely 

 different circumstances. 



Now, suppose that, the night before coming down to Brighton, you 

 had dreamed of a railway accident, caused by the engine getting 

 frightened at a flock of sheep, and jumping suddenly back over all the 

 carriages ; the result of which was that your head was unfortunately 

 cut off, so that you had to put it in your hat-box, and take it back 

 home to be mended. There are, I fear, many persons, even at this day, 

 who would tell you that, after such a dream, it was unwise to travel 

 by railway to Brighton. This is a proposal that you should take expe- 

 rience gained while you are asleep, when you have no common-sense 

 experience about a phantom-railway and apply it to guide you when 

 you are awake, and have common-sense, in your dealings with a real 

 railway. And yet this proposal is not dictated by scientific thought. 



Now, let us take the great example of biology. I pass over the 

 process of classification, which itself requires a great deal of scientific 

 thought, in particular when a naturalist, who has studied and mono- 

 graphed a fauna or a flora rather than a family, is able at once to pick 

 out the distinguishing characters required for the subdivision of an 

 order quite new to him. Suppose that we possess all this minute and 

 comprehensive knowledge of plants and animals and intermediate or- 

 ganisms, their affinities and differences, their structures and functions 

 a vast body of experience, collected by incalculable labor and devo- 

 tion. Then comes Mr. Herbert Spencer; he takes that experience of 

 life which is not human, which is apparently stationary, going on in 

 exactly the same way from year to year, and he applies that to tell us 

 how to deal with the changing characters of human nature and human 

 society. How is it that experience of this sort, vast as it is, can guide 

 us in a matter so different from itself? How does scientific thought, 

 applied to the development of a kangaroo-foetus, or the movement of 

 the sap in exogens, make prediction possible for the first time in that 

 most important of all sciences, the relations of man with man ? 



In the dark or unscientific ages men had another way of applying 

 experience to altered circumstances. They believed, for example, that 

 the plant called jew's-ear, which does bear a certain resemblance to 

 the human ear, was a useful cure for diseases of that organ. This doc- 

 trine of " signatures," as it was called, exercised an enormous influence 

 on the medicine of the time. I need hardly tell you that it is hope- 

 lessly unscientific ; yet it agrees with those other examples that we have 



