270 Mr. W. Brown on Steel Magnets. 



" The question,* which we are discussing at present, ma 

 therefore at once be reduced to this single point. Is the heat 

 which has the refrangibility of the red rays occasioned by the 

 light of these rays ? For, should that be the case, as there 

 will be then only one set of rays, one fate only can attend them, 

 in being either transmitted or stopped, according to the power 

 of the glass applied to them. We are now to appeal to our 

 prismatic experiment upon the subject, which is to decide the 

 question." The issue could not be more plainly stated. The 

 experiment is discussed, and this is the conclusion : — " Here 

 then we have a direct and simple proof, in the case of the red 

 glass, that the rays of light are transmitted, while those of 

 heat are stopped, and that thus they have nothing in common 

 but a certain equal degree of refrangibility. . . ." 



I am disposed to think that it was this erroneous con- 

 clusion from experiment fj more, perhaps, than preconceived 

 views about caloric, that retarded progress in radiant heat 

 for so many years. We are reminded of Darwin's saying 

 that a bad observation is more mischievous than unsound 

 theory. It would be interesting to inquire upon what 

 grounds we now reject the plain answer which Herschel 

 thought himself to have received from experiment. 1 do not 

 recall a modern investigation in which the heat and light 

 absorptions are proved to be equal for the various parts of the 

 visible spectrum. Can it be that after all we have nothing 

 but theory to oppose to Herschel's facts ? 



I hope it will be understood that these criticisms, even if 

 they are sound, do not touch the substance of Prof. Langley's 

 address, which is doubly interesting as coming from one who 

 has done so much himself to enlarge our knowledge of this 

 branch of science. 



XXX. JYote on Steel Magnets. By William Brown, " Thomson 

 Experimental Scholar,^'' now Demonstrator in Physics, Royal 

 College of Science, Dublin %. 



"lyr EARLY two years ago I brought before this Society the 

 -i-^ results of some experiments on the effects of percussion 

 in changing the magnetic moments of steel magnets, which 

 results were subsequently published in the March and May 



* Third Memoir, p. 520. 



t See Whewell's ' History of the Inductive Sciences,' vol. ii. p. 548 

 (1847). 



X Communicated by Sir William Thomson, having been read before the 

 Physical Society of Glasgow University, Oct. 12, 1888. 



