SCIENTIFIC USE OF THE IMAGINATION. 107 



qualities, let us handle it in accordance with strict 

 mechanical laws. Let us then carry our results from 

 the world of theory into the world of sense, and see 

 whether our deductions do not issue in the very phe- 

 nomena of light which ordinary knowledge and skilled 

 experiment reveal. If in all the multiplied varieties 

 of these phenomena, including those of the most remote 

 and entangled description, this fundamental conception 

 always brings us face to face with the truth ; if no 

 contradiction to our deductions from it be found in 

 external nature, but on all sides agreement and verifi- 

 cation ; if, moreover, as in the case of Conical Refraction 

 and in other cases, it actually forces upon our attention 

 phenomena which no eye had previously seen, and 

 which no mind had previously imagined such a con- 

 ception, must, we think, be something more than a 

 mere figment of the scientific fancy. In forming it, 

 that composite and creative power, in which reason and 

 imagination are united, has, we believe, led us into a 

 world not less real than that of the senses, and of which 

 the world of sense itself is the suggestion and, to a 

 great extent, the outcome. 



Far be it from me, however, to wish to fix you 

 immovably in this or in any other theoretic conception. 

 With all our belief of it, it will be well to keep the 

 theory of a luminiferous ether plastic and capable of 

 change. You may, moreover, urge that, although the 

 phenomena occur as if the medium existed, the absolute 

 demonstration of its existence is still wanting. Far be 

 it from me to deny to this reasoning such validity as it 

 may fairly claim. Let us endeavour by means of 

 analogy to form a fair estimate of its force. You be- 

 lieve that in society you are surrounded by reasonable 

 beings like yourself. You are, perhaps, as firmly con- 

 vinced of this as of anything. What is your warrant fojf 

 37 



