September 17, 1903] 



NATURE 



479 



I 



in the second jjroup, and from the third line in the 

 first group to the tliird line in the second group, when 

 measured in terms of oscillation frequencies to be 677- 1, 

 6770, and 6774. Similarly taking the second and third 

 groups it is 391-2, 391- 1, and 391 i. Between the third and 

 fourth groups in like manner it is 2309, 233, and 233; so 

 that the intervals diminish with increase of refrangibility 

 of the lines. 



In the zinc spectrum the intervals between the lines in 

 the first and second groups are 910, 910, and 910; in the 

 second and third groups 582, 581, and 583. 



In the cadmium spectrum the corresponding intervals are 

 801-5, 800. and 800 ; in the second and third groups 588, 

 589, and 587. The more accurately the lines are measured 

 the more exactly do these differences correspond. It is 

 scarcely necessary to point out that the differences in the 

 atomic masses of the elements are in round numbers where 

 H = I, Mg 24, Zn 65, and Cd 112. 



The Law of Constant Differences rendered il evident that 

 the spectra of the elements were subject to a law of homo- 

 logy, which was closely connected with the atomic mass 

 and with their chemical and physical properties. 



It was, in fact, found, in accordance with the periodic 

 law, that the spectra of definite groups were spectra 

 similarly constituted, from which it was deduced that they 

 are produced by similarly constituted molecules. It is 

 evident that there is periodicity in their spectra. The 

 rnetals studied being all monatomic in their molecular con- 

 dition, the conclusion was inevitable that the atoms were 

 of complex constitution, and that not only was the complex 

 nature of these atoms disclosed, but it was also shown that 

 groups of elements with similar chemical and physical 

 properties, the atomic weights of which differed by fixed 

 definite values, were composed of the same kind of matter, 

 but the matter of the different elements was in different 

 states of condensation, as we know it to be in different 

 members of the same homologous series of organic com- 

 pounds. If this were not the case, the mass or quantity 

 of matter in the atom would not affect in the same manner 

 its rate of vibration — which the facts observed lead us to 

 conclude that it does — and the chemical properties of the 

 substances would differ more widely from one another, and 

 the differences between them would not be gradational, 

 which in fact they are. It was thus impossible to believe 

 that the atoms were the ultimate particles of matter, though 

 so far as chemical investigations had proceeded they were 

 parts which had not been divided. Here the conviction was 

 forced upon one that matter might exist in a state which 

 had hitherto been unrecognised by those who accepted the 

 atomic theory without searching beneath it. All that the 

 atomic theory enabled the chemist to take account of were 

 the laws of combination and decomposition of the forms of 

 matter that are ponderable and of sufficient mass to be 

 weighable on the finest balances, which after all are but 

 crude and imperfect instruments for the study of matter, 

 since they are capable only of determining differences 

 between masses of tangible size. It became conceivable 

 that matter in the state of gas or vapour might become 

 so attenuated that repulsion of the molecules would be 

 greater than the attraction ; that they would then no longer 

 form aggregates, and in consequence would cease to be 

 weighable. In such a condition they may be imagined to 

 constitute the ether and in view of this' conception there 

 may be recognised four physical conditions of material sub- 

 stances, namely, solid, liquid, gas, and ether. 



It is more than twenty years ago since the study of 

 homology in spectra led me to the conviction that the 

 chemical atoms are not the ultimate particles of matter, 

 and that they have a complex constitution. 



That the atoms of definite groups of chemically related 

 elements are composed of the same kind of matter in 

 different states of condensation is not a dream or a view 

 of a visionary character, for it is based upon definite observ- 

 ations controlled by exact physical measurements, and is 

 therefore in the nature of a theory rather than an hypothesis. 

 Batchinski (1903) regards the atoms as being in a state 

 of vibration, and the periods of vibration of related elements 

 appear to stand in a simple relation to their properties. The 

 mass of an atom is proportional to the square of its period 

 of vibration, and conversely the vibration period of the atom 

 may be calculated from the' square root of the atomic weight. 



NO. 1768, VOL. 681 



These values have been calculated and arranged according to 

 Mendeleeff's classification, whereby it is shown that there 

 is a decided tendency to form harmonic series in the vertical 

 columns. The deviations are probably capable of explan- 

 ation, as the author believes, on the ground that the atom 

 is not to be regarded as a material point, but as a material 

 system. It is well to remember that the precursor of the 

 Periodic Law was Newland's Law of Octaves. 



I have always experienced great difficulty in accepting 

 the view that because the spectrum of an element contained 

 a line or lines in it which were coincident with a line or 

 lines in another element it was evidence of the dissociation 

 of the elements into simpler forms of matter. In my 

 opinion, evidence of the compound nature of the elements 

 has never been obtained from the coincidence of a line or 

 lines exclusively belonging to the spectrum of one element 

 with a line or lines in the spectrum exclusively belonging 

 to another element. This view is based upon the following 

 grounds : — First, because the coincidences have generally 

 been shown to be only apparent, and have never been proved 

 to be real ; secondly, because the great difficulty of obtain- 

 ing one kind of matter entirely free from every other kind 

 of matter is so great that where coincident lines occur in 

 the spectra of what have been believed to be elementary 

 substances they have been shown from time to time to be 

 caused by traces of foreign matter, such as by chemists are 

 commonly termed impurities ; thirdly, no instance has ever 

 been recorded of any homologous group of lines belonging 

 to one element occurring in the spectrum of another, except 

 and alone where the one has been shown to constitute 

 an impurity in the other ; as, for instance, where the triplet 

 of zinc is found in cadmium and the triplet of cadmium 

 in zinc ; the three strongest lines in the quintuple group 

 of magnesium in graphite, and so on. The latest elucida- 

 tion of the cause of coincidences of this kind arises out of 

 a tabulated record from the wave-length measurements of 

 about three thousand lines in the spectra of sixteen elements 

 made by Adeney and myself. The instances where lines 

 appeared to coincide were extremely rare ; but there was 

 one remarkable case of a group of lines in the spectrum 

 of copper which appeared to be common to tellurium ; also 

 lines in indium, tin, antimony, and bismuth which seemed 

 to have an origin in common with those of tellurium. 



It is difficult to separate tellurium from copper, and copper 

 fiom tellurium, by ordinary chemical processes. Dr. 

 Kothner, of Charlottenburg, has succeeded in obtaining 

 very pure tellurium from the spectrum of which these lines 

 and also several others have been almost entirely eliminated, 

 which shows that they are foreign to the element, and that 

 his specimen of tellurium is probably purer than any 

 previously obtained. For determining the atomic weight 

 of tellurium it is of course necessary to obtain it in the 

 greatest possible state of purity ; and it may be mentioned 

 that the material which Staudenmaier employed for this 

 purpose was found, from Kothner's photograph of its 

 spectrum, to be a very pure specimen. 



The prosecution of researches in connection with the 

 constitution of spectra was initiated by Johnstone Stoney, 

 by Balmer with respect to hydrogen, and continued by 

 Rydberg, Deslandres, Ames, and, above all, by Kayser and 

 Runge, who by an elaborate and exhaustive investigation 

 of the arc spectra of the elements have given us formulae 

 by which the wave-lengths of lines in the spectra of different 

 elements in certain definite groups may be calculated. They 

 also showed the spectra to be constituted of three series of 

 lines, the principal series and two subordinate series, one 

 sharp and the other diffuse. 



Ramage, however, has given us a simpler formula, de- 

 pending on the atomic weight, which applies to several 

 groups, and he has co-ordinated the spectra of several of 

 the elements with the squares of their atomic masses, and 

 also their atomic masses with other of their physical 

 properties. 



It may here be remarked that the homology of the spark 

 spectra in the magnesium, zinc, and cadmium series was 

 ai first called in question by Ames, though he proved the 

 arc spectra of zinc and cadmium to be strictly homologous. 



Preston decided the question by demonstrating by means 

 of beautiful photographs that corresponding lines such as 

 the pairs, triplets, and the quadruple groups in the spark 

 spectra of the three metals when under the influence of a 



