388 THE POPULAR SCIENCE MONTHLY. 



new as well as true in 1811 ; and if De la Roclie had not been re- 

 moved by an early death, his would have not improbably been 

 the greatest name of the century in the history of our subject ; an 

 honor, however, which was in fact reserved for another. 



The idea of the identity of light and radiant heat had by this 

 time made such progress that the attempt to polarize the latter 

 was made in 1818 by Berard. "We have just seen in Herschel's 

 case how the most sound experiment may lead to a wrong conclu- 

 sion, if it controverts the popular view. We now have the con- 

 verse of this in the fact that the zeal of those who are really in 

 the right way may lead to unsound and inconclusive experiment ; 

 for Berard experimentally established, as it was supposed, the fact 

 that obscure radiant heat can be polarized. So it can, but not 

 with such means as Berard possessed, and it was not till a dozen 

 years more that Forbes actually proved it. At this time, however 

 fairly we seem embarked on the paths of study which are followed 

 to-day, and while the movement of the main body of workers is in 

 the right direction, it is yet instructive to observe how eminent 

 men are still spending great and conscientious labor, their object 

 in which is to advance the cause, while the effect of it is to undo 

 the little which has been rightly done, and to mislead those who 

 have begun to go right. 



As an instance both of this and of the superiority of modern 

 apparatus, we may remark — after having noticed that the ability 

 of obscure heat to pass through glass, if completely established, 

 would be a strong argument in favor of its kinship to light, and 

 that De la Roche and others had indicated that it would do so (in 

 which we now know they were right) — that at this stage, or about 

 1816, Sir David Brewster, the eminent physicist, made a series of 

 experiments which showed that it would not so pass. Ten years 

 later, in view of the importance of the theoretical conclusion, 

 Baden Powell repeated his observations with great care, and con- 

 firmed them, announcing that the earlier experimenters were 

 wrong, and that Brewster was right. Here all these years of con- 

 scientious work resulted in establishing, so far as it could be 

 established, a wholly wrong conclusion in place of a right one 

 already gained. It may be added that, with our present appa- 

 ratus, the passage of obscure radiant heat through glass could be 

 made convincingly evident in an experiment which need not last 

 a single second. 



We are now arrived at a time when the modern era begins ; 

 and in looking back over one hundred and fifty years, from the 

 point of view of the experimenter himself, with his own statement 

 of the truth as he saw it, we find that the comparison of the prog- 

 ress of science to that of an army, which moves, perhaps with the 

 loss of occasional men, but on the whole victoriously and in one 



