September i6, 1920] 



NATURE 



H 



The existence of isotopes was first proved from 

 radio-active evidence. But besides possessing- the 

 radio-active characteristics of the atom, the 

 nucleus also carries its mass, and this suggests 

 that isotopes may differ in mass. The first evi- 

 dence for this can be derived from the study of 

 the figure. For example, uranium at 93 loses 

 an o-particle and two /3-particles, and thus 

 returns to 92 ; and the loss of the particles 

 must have reduced its weight from 238 to 234. 

 The same principle has been experimentally veri- 

 fied by finding that the atomic weight of lead from 

 radium is perceptibly different from that of 

 ordinary lead. We shall see in the next 

 article that ordinary elements also have 

 isotopes ; for convenience, these have been given 

 in the table, in so far as they have been yet dis- 

 covered. It should perhaps be here mentioned 



that the mere difference of atomic weight 

 theoretically implies certain minute differences in 

 chemical behaviour, but it can be shown that these 

 are out of all proportion less than those between 

 substances of different atomic number, so much 

 so that it is an almost impossibly laborious task 

 to separate isotopes by ordinary chemical or 

 physical processes. 



The general outcome of our argument has there- 

 fore been that atomic number, and not atomic 

 weight, is the determining factor in the behaviour 

 of an element. There are exceptions to this rule — 

 for example, specific heat depends directly on the 

 weight of the atom — but apart from these excep- 

 tions the importance which in the past the chemist 

 and spectroscopist have given to atomic weight 

 must in the future be attached to atomic number. 

 i^o he continued.) 



Obituary. 

 Prof. VVilhelm VVundt. 



\\MTH the death on September 1, at the 

 ' * advanced age of eighty-eight years, of 

 l'rt)f, W. Wundt a remarkable and striking 

 (K-rsonality passes away from the scientific world. 

 If, as a philosophic thinker, he did not possess 

 either the speculative genius or the insight of a 

 Herbart or a I.otze, he was yet a mind of extra- 

 ordinary versatility, whose comprehensive ac- 

 quaintance with vast fields of knowledge has 

 rarely, if ever, been rivalled. His amazing activity 

 .IS a writer has been for long a source of wonder 

 to his contemporaries ; year after year books, 

 pamphlets, and articles have issued from his 

 pen in steady succession, and there was no depart- 

 ment of philosophy which he thus left untouched. 

 Naturally, this tremendous literary output is not 

 all of equal worth, but almost everything he wrote 

 exhibits a surprising mastery of detail and power 

 of turning it to account in reaching theoretical 

 conclusions. As a teacher, too, his influence has 

 been extremely wide and far-reaching ; students 

 from all parts of the world met in his class-room, 

 and worked in the Institute of Experimental 

 Psychology at Leipzig, the foundation of which 

 was due to him. 



VVilhelm W'undt was born on August 16, 1832, 

 at N'eckarau, near Mannheim. In 185 1 he Ijegan 

 the study of medicine at Heidelberg, and in sub- 

 sequent semesters pursued his medical studies 

 further in Tiibingcn and Berlin. Vr. Arnold and 

 E. Hassc, of both of whom he always spoke with 

 great respect, were his teachers in Heidelljerg ; 

 while in Berlin Johannes Miillcr was then at the 

 height of his fame, and in the great man's labora- 

 tory Wundt was for some time busily engaged. 

 On the completion of hi> career as an under- 

 graduate, he turnCfl his attention first of all to 

 pathological anatomy, and took his degree in 

 Heidelberg in i886, his Arbeit being a thesis on 

 thr condition of the nerves in inflamed and de- 



vo. 2655. \"\ . 106] 



generated organs. In the following year he 

 habilitated in the Faculty of Physiology of the 

 same university, and remained in Heidelberg for 

 some years as Helmholtz's assistant in the physio- 

 logical laboratory. During that period he pub- 

 lished two monographs on physiological subjects 

 — the " Beitrage zur Lehre von den Muskelbewc- 

 gungen " (1858) and the " Beitrage zur Theorie der 

 SinneswahrnehiTiung " (1859-62) — in the long In- 

 troduction to the latter of which he first outlined 

 his conception of the scope of empirical psychology 

 as a natural science, and insisted upon the neces- 

 sity of using experimental methods in the obser- 

 vation of mental processes. It was in consequence 

 of his being occupied with the problems of sense- 

 perception that the young physiologist was in- 

 duced to enter the domain of metaphysical inquiry, 

 and started to read, "ziemlich ziel- und planlos," 

 as he tells us, the works of Kant, Herbart, and 

 Leibniz. The first fruits of these and of his more 

 strictly psychological labours saw the light in the 

 " Vorlesungcn iiber Menschen- und Thierseele " of 

 1863 — a volume in which, as he afterwards ex- 

 pressed it, he set about his task with more zeal 

 than discretion, and which he came to look upon 

 as containing the wild oats of his youthful days. 

 There followed in 1865 a text-book of "Human 

 Physiology" (which apparently had a large circu- 

 lation, a fourth edition appearing in 1878), and in 

 1867, when he was already a professor in Heidel- 

 berg, a voluminous treatise on what he called 

 " Medicinische Physik." intended to acquaint 

 medical students with the exact physical methods 

 needful in medical investigation. Probably the 

 most elaborate piece of experimental research 

 undertaken by himself was that of which account 

 is given in hi.s " Untersuchungen zur Mechanik der 

 Nerven und Nervencentrcn," the first part of which 

 was published in 187 1 and the second in 1876. 

 The bold and ingenious hypothesis, which he hete 



