Dfcemijer 5, 1907] 



NA TURE 



109 



mainly indebted to our Copley medallist. Not only did 

 he introduce the vacuum tube charged, with mercury or 

 cadmium as the best source of homogeneous light, but by 

 a most able use of an ingenious, method he determined, 

 with the highest precision, the values of the cadmium red, 

 green, and blue wave-lengths in terms of one another, and 

 of the metre. His work has been skilfully followed up by 

 Fabry and Perot, and. numerous wave-lengths are now 

 known with a relative accuracy of one millionth part. 

 When we reflect upon the almost ultra-microscopic magni- 

 tude of a wave-length of light, the possibility of such an 

 achievement may well excite our astonishment. 



For the advancement of science the main requirement 

 is, of course, original work of a high standard, adequately 

 e.\plaincd and published ; but this is not enough. The 

 advances so made must be secured, and this can hardly 

 be unless they are appreciated by the scientific public. 



In all the principal countries of the world we have now 

 a body of men professionally connected with science in its 

 various departments. No doubt the attention of many of 

 these is so engrossed by teaching that it would be hard 

 to expect much more from them, though we must re- 

 member that teaching itself takes on a new life when 

 touched with the spirit of original inquiry ; but in the older 

 uni\'('rsitics, at any rate, the advancement of science is one 

 of the first duties of professors. .Actual additions to know- 

 ledge occupy here the first place ; but there must be many 

 who, from advancing years or for other reasons, find 

 themselves unable to do much more work of this kind. 

 It is these I would exhort that they may fulfil their func- 

 tion in another way. If each man would mark out for 

 himself a field — it need not be more than a small one — 

 and make it his business to be thoroughly conversant with 

 all things, new and old, that fall within it, the danger of 

 which I have spoken would be largely obviated. A short 

 paper, a letter to a scientific newspaper, or even conversa- 

 tion with friends and pupils, would rescue from oblivion 

 writings that had been temporarily overlooked, thereby 

 advancing knowledge generally, and sometimes saving 

 from discouragement an unknown worker capable of 

 further achievements. Another service such experts might 

 render would be to furnish advice to younger men desirous 

 of pursuing their special subject. 



.''l movement is on foot, and has already, received valu- 

 able support, to promote the publication of standard scien- 

 tific works in embossed type suitable for the use of the 

 blind. Mr. H. M. Taylor tells me that in the course of 

 the last twelve months he has written out the whole of 

 Mr. C. Smith's " Elementary .Algebra " in Braille type, 

 has afterwards read the copy with his fingers, and again, 

 later, read the whole in proof. There can be no doubt that 

 books in embossed type on such subjects as mechanics, 

 physics, astronomy, geology, not to mention the various 

 biological sciences, would be an immense boon to many 

 blind readers. I commend the proposal heartily to your 

 notice. 



.'\nother remedy for the confusion into which scientific 

 literature is liable to fall may lie in the direction of restrict- 

 ing the amount of unessential detail that is sometimes 

 prevalent in the publication of scientific results. In com- 

 paring the outputs of the present time and of, sav, thirty 

 years ago, the most striking feature that appears is doubt- 

 less the increase of bulk, in recent years coming especially 

 from young workers stimulated by the healthv encourage- 

 ment of direct research as a part of scientific education. 

 But I think it may also be observed, and not alone in the 

 case of such early dissertations, that there is, on the whole. 

 1' 1^ care taken for the concise presentation of results, and 

 ili.it the main principles are often submerged under a 

 lluud of experimental detail. When the author himself has 

 not taken the trouble to digest his material or to prepare 

 it properly for the press, the reader may be tempted to 

 iudge of the care taken in the work from the pains taken 

 in its presentation. The tendency in some subjects to 

 submit for immediate publication the undigested contents 

 of note-books is one that we hear much of at the present 

 time. It is a matter that is difficult for publishing bodies 

 to deal with, excent by simple refusal of imperfectly pre- 

 pared material, with its danger of giving offence to authors 

 of recognised standinii:. but it seems not unlikely that at 

 present public scientific opinion would endorse such a 



NO. T988, VOL. ']']'\ 



course of action. A related difficulty, and one that con- 

 tributes to this trouble, is the tendency, noticeable in some 

 public scientific organisations, to imagine that their 

 activity is estimated by the number of pages of printed 

 matter they can produce in the year. Probably no con- 

 sideration is further removed, than this from the minds of 

 the educated public, whose judgment is alone worth 

 considering. 



Copley Medal. 



The Copley medal is awarded to Prof. Albert Abraham 

 Michelson, For.Mem.R.S., on the ground of his experi- 

 mental investigations in optics. 



In 1879 Michelson brought out a determination of the 

 velocity of light by an improved method, based on 

 Foucault's, which gave 299,980 kilometres per second. 

 Three years later, by means of a modification of the 

 method, capable of even greater precision, he found for 

 this constant, of fundamental importance for electric as 

 well as optical science, the value of 299,853 kilometres. 



.Michelson has been a pioneer in the construction of 

 interferometers, which are now indispensable in optics and 

 metrology. With his new instrument, at Paris, he deter- 

 mined the absolute wave-lengths of the red, green, and 

 blue lines of cadmium by counting the number of fringes 

 (twice the number of wave-lengths) corresponding to the 

 length of the standard metre of the Bureau International 

 dcs Poids et Mesures. He found the metre to be 1,553,164 

 times the wave-length of the red line of cadmium, a result 

 which is almost in exact agreement with the re-determin- 

 ation last year by Perot and Fabry. Michelson thus proved 

 the feasibility of an absolute standard of length, in wave- 

 lengths, of such accuracy, that if the standard metre were 

 lost or destroyed it could be replaced by duplicates which 

 could not be distinguished from the original. 



He had the greatest share in the elaboration of precise 

 experiments on the relative motion of ether and matter. 

 He repeated in an improved form Fi-esnel's experiment of 

 the speed of light in moving media, using water ::,nd 

 sulphide of carbon. He found that the fraction of the 

 velocity of the water by which the velocity of light is in- 

 creased is 0-434, with a possible error of +0-02. The 

 fact that the speed is less in water than in air shows 

 e.xperimentally that the corpuscular theory is erroneous ; 

 but his results, moreover, established the correctness of 

 Fresnel's formula for the effect, the theory of which has 

 since, become well understood. 



In conjunction with E. W. Morley, he devised and 

 carried out a very remarkable method by which, on the 

 assumntion of ether at rest, an effect depending on quanti- 

 ties of the order (vjV)- would appear to be appreciable. 

 No displacement of the fringes was found. Of this result 

 the simplest explanation would be that the ether near the 

 earth partakes fully in its orbital motion ; but modern 

 electric and optical science appears to demand a quiescent 

 ether, and the existence of this and similar null results 

 is fundamental for its theory. 



He has shown the possible application of the interfero- 

 meter method to astronomy, by himself measuring the 

 diameters of the four satellites of Jupiter, which are only 

 about one second of arc. He suggests the further appli- 

 cation of the instrument to such of the fixed stars as mav 

 not subtend less than one-hundredth of a second of arc. 



In 189S Michelson constructed a spectroscope which 

 enables us to make use of the great resolving powers of 

 the very high orders of spectra which are absent in the 

 use of the ordinary grating, and with the added advantage 

 of having most of the light in one spectrum. The echelon 

 consists of a pile of glass plates of precisely equal thick- 

 ness, which overlap by an equal amount ; with it spectral 

 lines which appear single with the most powerful gratings 

 can be resolved into components. This instrument has 

 been especially useful for the direct observation of the 

 imnortant, because definite, influence of magnetism o.i 

 light, discovered by Zeeman. With thirty plates, and 

 using the 25,000th spectrum, the echelon has a resolving 

 power of 750,000, while the most powerful gratings do 

 not exceed 100,000. 



In conni-ction with the analysis of radiations, he has 

 constructed and used various machines for the analysis 

 of periodic motions. For example, in conjunction with 



