2G6 Professor S. P. LanjUij [April 17, 



WG have thought from infancy will probably appear the sole possible 

 explanation, and that, if we want to break its chain, we should put 

 ourselves, at least in imagination, under conditions where it no longer 

 binds us. 



The ' Challenger ' has dredged from the bottom of the ocean fishes 

 wliich live habitually at great depths, and \Yhose enormous eyes tell 

 of the correspondingly faint light which must liave descended to them 

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

 speculation as it may at fi)-st 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 w^ere 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 splendour of the sun, shining through a medium 

 wliich all his ex^Dcrience 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 colourless 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 colourless, and that pure 

 sunlight is white, so that if I venture to ask you to listen to con- 

 siderations 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 educated intelligence possesses those senses equally, and 

 in addition the ability to interpret them by the light of reason, 

 and before this audience 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 coloured or not? It seems 

 nearly colourless ; but have we any right to conclude that it is so 

 because it seems so r Are we not faking it for granted that the 

 original light which we see through it is white, and that the glass is 

 colourless, because 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 colours, and that whether 

 the original light is really white and the glass transi^rent, or the 

 glass really coloured 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, wliich was not colourless, but of a deep 



