240 



NATURE 



[October 28, 19 15 



by Lister and others, some species exhibit viviparous 

 reproduction and the budding-off of young individuals. 

 The viviparous young are formed inside the parent 

 shell and emerge by the dissolution of the base. The 

 process demands a sacrifice of the whole of the proto- 

 plasm and of the internal septa, whereas in zoospore- 

 production the shells of the young are formed outside 

 the parent, from material derived from the surround- 

 ing medium, and not from the internal septa. Another 

 method of multiplication is to bud-off a young indi- 

 vidual from the shell-aperture of the parent. To this 

 process and to the occasional (possibly fortuitous) 

 mingling of the extruded protoplasm of two or more 

 shells, is generally attributable what has been described 

 as "plastogamy" in the Foraminifera. 



In regard to shell-making, Mr. Heron-Allen has 

 some remarkable evidence to submit of a quality which 

 he calls "intelligence," or "an apparent development 

 of purpose." The Foraminifer may select out of a 

 large supply of possibilities one particular kind of 

 material, such as sponge-spicules, minute flakes of 

 mica, Echinoderm plates, and it may use this mate- 

 rial in a purposive way. Thus in Technilella legumen 

 "the whole shell wall consists of two distinct layers 

 of spicules, an outer layer in which the spicules 

 are all laid down with their long axes parallel to the 

 long axis of the test, and an inner layer of spicules 

 laid with their long axes at right angles to the outer 

 layer, giving as close an approximation to the woof 

 and warp of a textile fabric as is possible with a rigid 

 non-flexible material such as sponge-spicules. It is 

 obvious that by the crossing of these two layers the 

 strength and resistance of the test to strain is enor- 

 mously increased." 



Or again, while Marsipella cylindrica forms a long 

 and very friable tube of broken sponge-spicules, " it 

 was left for M. spiralis to make the same great dis- 

 covery as did the prehistoric genius who invented 

 string — it has clearly realised that a twisted yarn is 

 stronger than an untwisted wisp of fibre." The 

 author maintains that " the Foraminifera exhibit the 

 highest functions and the most ' intelligent behaviour ' 

 of which undifferentiated protoplasm has been observed 

 to be capable." 



MATHEMATICAL AND PHYSICAL SCIENCE 

 AT THE BRITISH ASSOCIATION. 



T^HE Section of Mathematical and Physical Science 

 -*■ met under the presidency of Sir F. W. Dyson, 

 whose address on the construction of the heavens 

 appeared in Nature of September 9. 



Radio-active Elements and the Periodic Law. 

 Following the address, a discussion on radio-active 

 elements and the periodic law took place. The 

 opener. Prof. F. Soddy, explained that the discovery 

 of a large number of radio-active disintegration pro- 

 ducts seemed at first difficult to reconcile with the 

 periodic table of the elements ; for it w'as clear that 

 the existing gaps would not provide for more than 

 a few of them. But it had been found that among 

 them there were only three new separable elements 

 — radium, polonium, and actinium ; the others were 

 isotopes of known elements, i.e., they had identical 

 chemical properties, although differing somewhat in 

 atomic weight. The fundamental discovery, \vhich 

 brought order amongst these diverse products, was 

 that when an a particle was expelled a shift of two 

 places to the left in the table took place, whilst the 

 expulsion of a /3 particle caused a shift of one place 

 to the right. Since an a particle carries two positive 

 charges, and a P particle one negative charge, this 

 suggests that position in the periodic table is a 



NO. 2400, VOL. 96] 



function of the charge. Moseley's work has ex- 

 tended this by showing that it is true from end to 

 end of the periodic table. Another fundamental fact 

 is Rutherford's discovery of the nucleus of the atom, 

 which was detected by experiments in scattering. 

 We arrive at the conclusion that isotopes have the 

 same net nuclear charge, though the gross number 

 of positive and negative charges differs. Isotopes 

 cannot be separated by chemical means, and hitherto 

 diffusion methods have been unsuccessful. In view 

 of the numerous isotopes of lead the question of 

 the variability of the atomic weight of lead derived 

 from different minerals becomes important ; variations 

 from 20605 (uranium lead) to 207-67 (thorite lead) 

 have been found. The new view of the periodic 

 table is that it is a relation between chemical char- 

 acter and nuclear charge, not between character and 

 mass ; and it is possible now to state that there are 

 exactly 92 elements up to uranium (counting iso- 

 topes as one element), of which 86 are known. 

 We seem to be returning to the view of the Greeks 

 and alchemists that elements are qualities, in contrast 

 to the later view that elements are constituents. 



Dr. N. Bohr pointed out that the dimensions of 

 the nucleus are so small compared with the outer 

 rings of electrons, that the nuclear constitution would 

 have negligible effect on the electric field in these 

 outer parts, only the net charge being important. 

 Consequently, properties depending on the outer 

 rings of electrons would be the same for all isotopes. 

 In the case of spectral vibrations, there occurs a small 

 term depending on the mass of the central nucleus, 

 and accordingly we ought to look out for a small 

 but perceptible difference between the spectra of two 

 isotopes. Dr. F. A. Lindemann gave a theoretical ■ 



argument to show that you could not have identical I 



chemical and physical properties when the atomic ■ 



weight differed. If the chemical properties were the 

 same, certain physical properties must differ, and 

 vice versd. Mr. A. Fleck compared the effects of 

 taking away charges from uranium, (a) by reduction 

 (uranous salts), and (b) by disintegration (UrX salts). 

 Dr. Whytlaw Gray described experiments on minute 

 quantities of RaD, showing that it answered the 

 chemical tests for lead. He thought it would not 

 be difficult to observe its melting point directly. Sir 

 E. Rutherford said that it was surprising how simply 

 the whole system of thirty-four new products had been 

 absorbed in the periodic table. In one case we have 

 seven isotopes, all radio-active except one (Pb). 

 Those which show radio-activity are distinguishable 

 from one another by that property. Several references 

 were made to the loss of Mr. H. G.-J. Moseley, 

 killed at the Dardanelles, to whose researches this 

 subject has owed so much. 



The Order of Stellar Evolution. 

 On Thursday morning. Prof. A. Fowler opened a 

 discussion on spectral classification of stars and the 

 order of stellar evolution. He described the order of 

 the types of stellar spectrum, which, according to the j 



Draper notation, form the sequence O, B, A, F, G, jj 



K, M, and pointed out that this sequence has come ^ 

 to be regarded not merely as a convenient mode 

 of description, but as actually representing successive 

 stages of evolution. The spectra present striking 

 evidence of a continuity extending from one end to i 

 the other of the sequence, and there are links con- I 

 necting the earliest type, O, to the gaseous nebulae. ^ 



The temperatures of the stars decrease in the order 

 of the sequence from upwards of 10,000° C. for the 

 B stars to 3000° C. for the M stars, and at the same 

 time the colour changes continuously from white to 

 red. Additional evidence in support of the sequence 



