340 



NA TURE 



[August q, 1894 



three centuries ola. But the mental sciences which were sup- 

 posed to rest upon hi'; writings have retained some of their as- 

 cendency even till this day, and have only slowly and jealously 

 admitted the rivalry of the growing sciences of observation. 

 The subject is interesting to us, as this undecided state of 

 feeling coloured the experiences of this .Association at 

 its last O.xford visit, nearly a generation later, in 

 1S60. The warmth of the encounters which then took place 

 have left a vivid impression on the minds of those who aie old 

 enough to have witnessed them. That much energy was on 

 that occasion converted into heat may, I think, be inferred from 

 the mutual distance which the two bodies have since main- 

 tained. Whereas the visit of 1S32 was succeeded by another 

 visit in fifteen years, and the visit of 1S47 was succeeded by 

 another visit in thirteen years, the year 1S60 was followed by a 

 long and dreary interval of separation, which has only now, 

 after four-and- thirty years, been terminated. It has required 

 the lapse of a generation to draw the curtain of oblivion over 

 those animated scenes. It was popularly supposed that deep 

 divergences upon questions of religion were the motive force of 

 those high controversies. To some extent that impression was 

 correct. But men do not always discern the motives which are 

 really urging them, and I suspect that in many cases religious 

 apprehensions only masked the resentment of the older learning 

 at the appearance and claims of its younger rival. In any case 

 there is something worthy of note, and something that conveys 

 encouragement, in the ditTcrence of the feeling which prevails 

 now and the feeling that was indicated then. Few men are 

 now inlluenced by the strange idea that questions of religious 

 belief depend on the issues of physical research. Few men, 

 whatever their creed, would now seek their geology in the 

 books of their religion, or, on the other hand, would fancy that 

 the laborator)' or the microscope could help them to penetrate 

 the mysteries which hang over the nature and the destiny of the 

 soul of man. And the old learning no longer contests the share 

 in education which is claimed by the new, or is blind to the 

 supreme influence which natural knowledge is exercising in 

 moulding the human mind. 



A study of the addresses of my learned predecessors in this 

 oflice shows me that the main duty which it falls to a President 

 to perform in his introiluctory address, is to remind you of the 

 salient points in the annals of science since last the Association 

 visited the town in which he is speaking. Most of them have 

 been able to lay before you in all its interesting detail the history 

 of the particular science of which each one of them was the 

 eminent representative. If I were to make any such attempt I 

 should only be telling you with very inadequate knowledge a 

 story which is from time to lime told you, as well as it can be 

 told, by men who are competent to deal with it. It will be 

 more suitable to my cap.icity if I devote the few observations I 

 have to make to a survey n')t of our science but of our ignorance. 

 NVe live in a small bright oasis of knowledge surrounded on all 

 sides by a vast unexplored region of impenetrable mystery. 

 From age to age the strenuous labour of successive generations 

 wins a small strip from the desert and pushes forward the 

 boundary of knowledge. Of such triumphs we are justly proud. 

 It is a less attractive task — but yet it has its fascination as well 

 a.s its uses — to turn our eyes to the undiscovered country which 

 still remains to be won, to some of the stupendous problems of 

 ii.Tiural study which Mill defy our investigation. Instead, iherc- 

 f'T'-, iif recounting to you what has been done, or trying to 

 furtc.isi the rliscovcries of the future, T would rather draw your 

 attention to the condition in which we stand towards three or 

 four of the most important physical questions which it has been 

 the cflfort of the Inst century to solve. 



Of the scientific enigmas which still, at the end of the nine- 

 icrnlh century, defy solution, the nature and origin of what are 

 <;.ilic'l the elements is the most notable. It is not, perhaps, easy 

 "1 gn'e a precise logical rea.son for the feelmg that the existence 

 of oar sixty-five elements is a slrance anomaly and conceals 

 some much timpler itatc of facts. Bui the conviction is irre- 

 sistible. We cannot conceive, on any possible doctrine of cos- 

 monony, how these »ixty five elements came into existence. A 

 ■"^ ' ' '^ in form the substance of this planet. Another third 

 , but somewhat rare. The remaining third are 

 -attcred haphazard, but very scantily, over the globe, 

 with no other apparent function but to provide occupation (01 

 the collector and the chemist. Some of them are so like each 

 other that only a chemist can tell them apart : others differ im- 

 measurably from each other in every conceivable particular. In 



NO. I 293, VOL. 50] 



cohesion, in weight, in conductivity, in melting point, in chem- 

 ical proclivities they vary in every degree. They seem to have 

 as much relation to each other as the pebbles on a sea beach, or 

 the contents of an ancient lumber room. Whether you believe 

 that Creation w.as the work of design or of inconscient law, it 

 is equally difficult to imagine how this random collection of dis- 

 similar materials came together. Many have been the attempts 

 to solve this enigma ; but up till now they have left it 

 more impenetrable than before. -V conviction that here was 

 something to discover K-iy beneath the persistent belief 

 in the possibility of the transmutation of other metals 

 into gold, which brought the alchemy of the Middle Ages into 

 being. When the immortal discovery of Dalton established 

 that the atoms of each of these elements have a special weight 

 of their own, and that consequently they combine in fixed 

 ponderable proportions from which they never depart, it re- 

 newed the hope that some common origin of the elements was 

 in sight. The theory was advanced that all these weights were 

 multiples of the weight of hydrogen — in other words, that each 

 elementary atom was only a greater or a smaller number of 

 hydrogen atoms compacted by some strange machinery into one. 

 The most elaborate analyses, conducted by chemists of the 

 highest eminence — conspicuously by the illustrious Stas— were 

 directed to the question whether there was any trace in fact of 

 the theoretic idea that the atoms of each element consist of so 

 many atoms or even of so many half-atoms of hydrngen. Rut 

 the reply of the laboratories has always been clear and certain 

 — that there is not in the facts the faintest foundation for such 

 a theory. 



Then came the discovery of the spectrum analysis, and men 

 thought that with an instrument of such inconceivable tielicacy 

 we should at last find out something as to the nature of tlie.atom. 

 The result has been wholly disappointing. Spectrum analysis 

 in the hands of Dr. Huggins and .Mr. Lockyer and others h.as 

 taught us things of which the world little exptcted to be told. 

 We have been enabled to measure the speed with which clouds 

 of blazing hydrogen course across the surface of the sun ; 

 we have learnt the pace — the fabulous pace — at which the most 

 familiar stars have been for ages approaching to or receding 

 from our planet, without apparently affecting the proportions 

 of the patterns which as far as historical record goes back thev 

 have always delineated on the evening sky. We have received 

 some information about the elementary atoms themselves. We 

 have learnt that each sort of atom when heated strikes upon the 

 ether a vibration, or set of vibrations, whose r.ate is all its own ; 

 and that no one atom or combination of atoms in producing its 

 own spectrum encroaches even to the extent of a single line upon 

 the spectrum that is peculiar to its neighbour. We have learnt 

 that the eleuienls which exist in the stars and speci.ally in the 

 sun are mainly those with which we are familiar upon earth. 

 There are a few lines in excess to which we can give no 

 terrestrial name ; and there are some still more puzzling gaps in 

 our list. It is a great aggravation of the mystery which besets 

 the fpiestion of the elements, that among the lines which are 

 absent from the spectrum of the sun, those of nitrogen ami 

 oxygen stand first. Oxygen constitutes the largest portion of 

 the solid and litiuid subst-ince of our planet, so far as we know 

 it ; and nitrogen is very far the predominant constituent of our 

 atmosphere. If the earth is a detached bit whirled oil' the mass 

 of the sun, as cosmogonists love to tell us, how comes it that in 

 leaving the sun we cleaned him out so completely of his nitrogen 

 and oxygen that not a trace of these gases remains bchinil to be 

 discovered even by the sensitive vision of the spectroscope ? 



All these things the discovery of the spectrum analysis has 

 added to our knowledge ; but it has left us as ignorant as ever 

 as to the nature of the capricious differences which separate the 

 atoms from each other, or the cause to which those differences 

 are due. 



In the last few years the same enigma has been approached 

 from another point of view by Prof. Mendelieff. The periodic 

 law which he has discovered redccls on him all the honour that 

 can be earned by ingenious, laborious, and successful research. 

 lie has shown that this perplexing list of elements can be di- 

 videil into families of about seven, speaking very rou;jhly : that 

 those familic- all resemble each other in this, that as to weight, 

 volume, licat, and laws of combination, the members of each 

 family are ranked among themselves in obedience Id the same 

 rule. Fach family differs from the others ; but each inlernally 

 is constructed upon the same plan. It was a strange iliscovery 

 — strangest of all in its manifest defects. For in the plan id his 



