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tions from it be found in external nature j if, moreover, 

 it has actually forced upon our attention phenomena 

 which no eye had previously seen, and which no mind 

 had previously imagined ; if by it we are gifted with a 

 power of prescience which has never failed when 

 brought to an experimental test ; such a conception, 

 which never disappoints us, but always lands us on the 

 solid shores of fact, must, we think, be something more 

 than a mere figment of the scientific fancy. In forming 

 it that composite and creative unity in which reason and 

 imagination are together blent, 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 

 justification. 



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

 ably in this or in any other theoretic conception. With 

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

 plastic and capable of change. You may, moreover, 

 urge that although the phenomena occur as if the me- 

 dium existed, the absolute demonstration of its exist- 

 ence is still wanting. Far be it from me to deny to this 

 reasoning such validity as it may fairly claim. Let us 

 endeavor by means of analogy to form a fair estimate 

 of its force. 



You believe that in society you are surrounded by 

 reasonable beings like yourself. You are, perhaps, as 

 firmly convinced of this as of anything. What is your 

 warrant for this conviction ? Simply and solely this, your 

 fellow-creatures behave as if they were reasonable ; the 

 hypothesis, for it is nothing more, accounts for the facts. 

 To take an eminent example, you believe that our pres- 

 ident is a reasonable being. Why ? There is no known 

 method of superposition by which any one of us can 



