64+ THE POPULAR SCIENCE MONTHLY. 



The Challenger has dredged from the bottom of the ocean fishes 

 which live habitually at great depths, and whose enormous eyes tell 

 of the correspondingly faint light which must have descended to them 

 through the seemingly transparent water. It will not be as futile a 

 speculation as it may at first seem, to put ourselves in imagination in 

 the condition of creatures under the sea, and ask what the sun may 

 appear to be to them ; for, if the fish who had never risen above the 

 ocean-floor were an intelligent being, might he not plausibly reason 

 that the dim greenish light of his heaven which is all he has ever 

 known was the full splendor of the sun shining through a medium 

 which all his experience shows is transparent ? 



We ourselves are, in very fact, living at the floor of a great aerial 

 sea, whose billows roll hundreds of miles above our heads. Is it not 

 at any rate conceivable that we may have been led into a like fallacy 

 from judging only by what we see at the bottom ? May we not, that 

 is, have been led into the fallacy of assuming that the intervening 

 medium above us is colorless because the light which comes through it 

 is so ? 



I freely admit that all men, educated or ignorant, appear to have 

 the evidence of their senses that the air is colorless, and that pure sun- 

 light is white, so that if I venture to ask you to listen to considerations 

 which have lately been brought forward to show that it is the sun 

 which is blue, and the air really acts like an orange veil or like a sieve 

 which picks out the blue and leaves the white, I do so in the confidence 

 that I may appeal to you on other grounds than those I could submit 

 to the primitive man who has his senses alone to trust to ; for the edu- 

 cated intelligence possesses those senses equally, and in addition the 

 ability to interpret them by the light of reason, and before this audi- 

 ence it is to that interpretation that I address myself. 



Permit me a material illustration. You see through this glass, 

 which may typify the intervening medium of air or water, a circle of 

 white light, which may represent the enfeebled disk of the sun when 

 so viewed. Is this intervening glass colored or not ? It seems nearly 

 colorless ; but have we any right to conclude that it is so because it 

 seems so ? Are we not taking it for granted that the original light 

 which we see through it is white, and that the glass is colorless, be- 

 cause the light seems unaltered ; and is not an appeal to be made here 

 from sense to reason, which, in the educated observer, recalls that white 

 light is made of various colors, and that whether the original light is 

 really white and the glass transparent, or the glass really colored and 

 so making the white, is to be decided only by experiment, by taking 

 away the possibly deceptive medium ? I can take away this glass, 

 which was not colorless, but of a deep orange, and you see that the 

 original light was not white, but intensely blue. If we could take the 

 atmosphere away between us and the sun, how can we say that the 

 same result might not follow ? To mak the meaning of our illustra- 



