596 RHPORT— 1903. 



of each metal of the group, and were clearly associated with the atomic mass and 

 chemical properties in each case. 



The arrangement of the lines, which was common to all the metals in the 

 magnesium, zinc, cadmium group, may shortly be described as follows: — Three 

 isolated lines and one pair of lines in magnesium, with four sets of triplets ; one 

 isolated line and one pair of lines in zinc, with three sets of triplets ; one isolated 

 line and one pair of lines in cadmium, with three sets of triplets. 



Besides the arrangement of these lines there were in the spectrum of each 

 element two groups of the most refrangible lines, consisting one of a quadruple 

 group and the other of a quintuple group, the groups and the lines composing 

 them being similarly disposed in each spectrum. It was, however, not distinctly' 

 proved that these particular groups were strictly homologous, the most refrangible 

 lines in the zinc spectrum being very difficult to photograph even on specially 

 prepared plates, though the lines are strong. It was furthermore observed that 

 with an increase in the atomic mass the distances between the lines both in 

 pairs and triplets were greater. The same was the case with the quadruple and 

 quintuple groups. In the magnesium spectrum, if we compare the first with the 

 second group of triplets, we find the intervals extending from the first line in the 

 first group to the first line in the second group, and from the second line in 

 the first group to the second line in the second group, and fi*om the third line in the 

 first group to the third line in the second group, when measured in terms of 

 oscillation frequencies to be 677*1, 677"0, and 677'4. Similarly taking the second 

 and third groups it is 39r2, 39]'l, and 391'1. Between the third and fourth 

 groups in like manner it is 230'9, 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 o82, 581, and -583. 



In the cadmium spectrum the corresponding intervals are 801 -5, 800, and 800; 

 in the second and third groups 688, 589, and 587. The more accurately the lines 

 are measured the more exactly do these diflerences 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 Laiv of Constajit Differences rendered it evident that the spectra of the 

 elements were subject to a law of homology, 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 metals studied being all monatomic in their 

 molecular condition, 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 compounds. 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 



