20 S. P. Langley — The History of a Doctrine. 



autumn and winter had passed, each season giving its own 

 testimony ; and this for successive years. The final conclusion 

 was irresistible, that the universal statement of this alleged 

 well-known fact, inexplicable as this might seem, in so simple 

 a matter, was directly contradicted by experiment. I had 

 some natural curiosity to find how every one knew this to be a 

 fact; but search only showed the same statement (that the 

 earth's atmosphere absorbed dark heat like glass) repeated 

 everywhere, with absolutely nowhere any observation or evi- 

 dence whatever to prove it, but each writer quoting from an 

 earlier one, till I was almost ready to believe it a dogma supe- 

 rior to reason, and resting on the well-known " Quod semper, 

 quod ubiqite, quod ab omnibus, creditum est." Finally I 

 appear to have found its source in the writings of Fourier, 

 who, alluding to De Saussure's experiments (which showed 

 that dark heat passed with comparative difficulty through 

 glass) observes that if the earth's atmosphere were solid, it 

 would act as the glass does. Fourier simply takes this (in 

 which he is wrong) for granted ; but, as he is *an authority on 

 the theory of heat, his words are repeated without criticism, 

 first by Poisson, then by others, and then in the text-books ; 

 and, the statement gaining weight by age, it comes to be be- 

 lieved absolutely, on no evidence whatever, for the next sixty 

 years, that our atmosphere is a powerful absorber of precisely 

 those rays which it most freely transmits. 



The question of fact here, though important, is, I think, 

 quite secondary to the query it raises as to the possible unsus- 

 pected influence of mere tradition in science, when we do not 

 .recognize it as such. ]STow, members of any church are doubt- 

 less consistent in believing in traditions, if they believe that 

 these are presented to them by an infallible guide ; but are we, 

 who have no infallible guide, quite safe in believing all we do, 

 from our fond persuasion that in the scientific body mere tra- 

 dition has no weight ? 



In even this brief sketch of the growth of the doctrine of 

 radiant energy, we have perhaps seen that the history of the 

 progress of this department of science is little else than a 

 chapter in that larger history of human error which is still to 

 be written, and which, it is safe to say, would include illustra- 

 tions from other branches of science, as well as my own. But 

 — and here I ask pardon if I speak of myself — I have been 

 led to review the labors of other searchers from this stand- 

 point, because I had first learned, out of personal experience, 

 that the greatest care was no certain guaranty of final accuracy ; 

 that to labor in the search for a truth with such endless pains 

 as a man might bestow if his own salvation were in question, 

 did not necessarily bring the truth ; and because, seeking to 



