S. P. Langley — The History of a Doctrine. 19 



other bodies, are merely effects of this mysterious thing we 

 call radiant energy, without doing more in this than give a 

 name to the ignorance which still hangs over the ultimate 

 cause. 



I am coming down dangerously near our own time, for one 

 who would be impartial in dealing with names of those still 

 living. In such a brief review of this century's study of 

 radiant energy in other forms than light, it has been necessary 

 to pass without mention the labors of such men as Pouillet 

 and Becquerel in France, of Tyndall in England, and of 

 Henry in America. It has been necessary to omit all mention 

 of those who have advanced the knowledge of radiant energy as 

 light, or I should have had to speak of labors so diverse as those 

 of Fraunhofer, of Kirchhoff, of Fresnel, of Stokes, of Lockyer, 

 of Janssen, and many more. I have made no mention, in the 

 instructive history of error, of many celebrated experimental 

 researches ; in particular of such a problem as the measure- 

 ment of solar heat, great in importance, but apparently most 

 simple in solution, yet which has now been carried on from 

 generation to generation, each experimenter materially alter- 

 ing the result of his predecessor, and 'where our successors will 

 probably correct our own results in turn. I have not spoken 

 of certain purely experimental investigations, like those of 

 Dulong and Petit, which have involved immense and consci- 

 entious labor, and have apparently rightly earned the name of 

 "classic" from one generation, only to be recognized by the 

 next as leading to untrustworthy results, and leaving the work 

 to be done again with new methods, guided by new principles. 



In these instances, painstaking experiments have proved 

 insufficient, less from want of skill in the investigator than 

 from his ignorance of principles not established in time to 

 enable him to interpret his experiments ; but, if there were 

 opportunity, it would be profitable to show how inexplicably 

 sometimes error flourishes, grows, and maintains an apparently 

 healthy appearance of truth, without having any root what- 

 ever. Perhaps I may cite one instance of this last from my 

 own experience. 



About ten years ago it was generally believed that the 

 earth's atmosphere acted exactly the part of the glass in a hot- 

 bed, and that it kept the planet warm by exerting a specially 

 powerful absorption on all infra-red rays. I had been reared 

 in the orthodox scientific church, of which I am happy to be 

 still a member ; but I had acquired perhaps an almost undue 

 respect, not only for her doctrines, but for her least sayings. 

 Accordingly, when my own experiments did not agree with 

 the received statement, I concluded that my experiments must 

 be wrong, and made them all over again, till spring, summer, 



