ANOTHER LESSON FROM TEE RADIOMETER. 



301 



and through them on Christian versions and ex- 

 positions. In some cases the literal or Babylo- 

 nian Targums have a text differing from the Mas- 

 oretic. But it is not unlikely that, if we had a 



satisfactory text of the Targums (toward which 

 almost nothing has hitherto been done), these 

 variations would find their explanation in the 

 Eastern text and the Assyrian punctuation. 



ANOTHER LESSON FROM THE RADIOMETER. 



By WILLIAM CKOOKES, F. E. S. 



THE great aim of the writer who criticises or 

 popularizes scientific discoveries should be 

 accuracy. He who misrepresents, and then re- 

 futes, not what has been really advanced by the 

 author, but what has been foisted upon him, lays 

 himself open to the gravest censure. The business 

 of the critic is to investigate, to digest, and then 

 to describe, briefly perhaps, but so as not to lead 

 astray. If there are before him errors of fact, 

 let them be pointed out ; if false conclusions, let 

 them be refuted. No mistake in doctrine or 

 method, in matter or manner, should be passed 

 over. On the other hand, the critic should re- 

 member that experimental research is necessa- 

 rily and slowly progressive, and that the early 

 provisional hypothesis has to be modified, ad- 

 justed, perhaps altogether abandoned, in defer- 

 ence to later observations. We do not censure 

 the dawn for not being full daylight, nor should 

 an author's more advanced researches be used 

 to condemn and to discredit his first gropings 

 after truth. 



In an " age of research " it is of consequence, 

 too, that the work of critical examination should 

 be intrusted to competent hands. And who 

 should interpret to the public the results of the 

 investigator ? There is but one answer to this 

 question. The only fully competent authority is 

 a specialist versed in the department he under- 

 takes to criticise. He only is adequately alive to 

 what has previously been done, and can best es- 

 timate the difficulties that beset a complicated 

 inquiry. He alone can pronounce most authori- 

 tatively on the validity of the methods employed, 

 can appreciate the solutions arrived at, and can 

 point out the collateral issues opened up. There 

 should be specialists and specialists, and a spe- 

 cialist trained in one department is rarely fitted to 

 pronounce upon the work of a specialist in an- 

 other and totally distinct department. 



The April number of the Nineteenth Century 

 contains an article bearing the signature of Dr. 



W. B. Carpenter, and ostensibly treating of the 

 " Radiometer and its LessoDS." The description 

 of the instrument itself and of its reception in 

 scientific circles contains little perhaps openly or 

 strikingly erroneous, but unfortunately Dr. Car- 

 penter has endeavored to combine matters which 

 have no possible connection with the radiome- 

 ter ; moreover, the omissions and inaccuracies 

 which occur in his historical review of my experi- 

 ments and published researches on the subject 

 would seem to deprive his inferences and conclu- 

 sions of any value which they otherwise might 

 have possessed. 



We are told ' that when the theory of the ra- 

 diometer was under discussion at the Royal So- 

 ciety Prof. Stokes confined himself to the state- 

 ment that " such mechanical action must lie out- 

 side the undulatory theory, which deals only with 

 light as light — i. e., as producing visual phenome- 

 na." The last four words are added by Dr. Car- 

 penter to the observations of Prof. Stokes. That 

 the undulatory theory gives no account of the 

 phenomena of light, save so far as they are con- 

 nected with the vision of man and animals, is, to 

 say the least, a startling revelation. 



Again, we read 2 that when the movement of 

 the radiometer was discussed " it was noticed by 

 several as anomalous, that the black should be 

 the "driving" side of the disks, since it might 

 have been anticipated that the mechanical action 

 of light would manifest itself in pushing away 

 the surface from which its rays are reflected, and 

 that the surface into which they are absorbed 

 would move toward the source from which 

 the rays emanate." Dr. Carpenter here omits 

 the explanation of this apparent anomaly given 

 by me at the Royal Society, and accepted as 

 satisfactory by the eminent physicists present, 

 to the effect that the rays falling on the white 

 surface are simply reflected off without doing any 

 work ; but the rays falling on the black surface 

 i P. 244. a Ibid. 



