420 



SuppUvtent to "'Natures' September 15, 1923 



I 



This !'M<'r If vi'ill '"• r.i rilliil <I<:il>; villli llw IwiWCr 



poss( the 



capa! I ' is .iiMi T/Uium 



of pi.: . . thiin. 



The adiaiiaiii iivpiiii' • ' ' T'hrcnfcst 



is discussed, ami al-,n tin 1; m < (in- 



junction with the (jii.mtimi Iht.'ix iii rli,' 

 Zeeman effects (it till' noiiiiai I v|)i-. KclniiK c . 

 us Well, til the intric iiirj and suggestive attempts ul 

 HeisenlurL; and Smiihim ih Id to find in a development 

 of the (luaiiiiiin ili((ii\ an i\i)laiiation of the anomalous 

 Zeeman ctTn l txhihiled t>\ ( citaiii classes of spectral 

 \\\\v>. In tliis aj){)licali(in (il the i|uantuni tlicury it 

 is assumed that the doublet sc[)arati"" ' !■-' " lfn>t m 

 of series such as those of the ar( .Npi • dk di 



elements arc in reality Zeeman separaLuiii> jumiuced by 

 intra atmnu magnetic fields. In conclusion there are 

 illustrations of the magnitude of such intra-atomic 

 magnetic fields, and a discussion of some of the diffi- 

 culties raised by HeisenlnrL^ and Sommerfeld's theory 

 and of some objections lu ihe way of its immediate 

 and general acceptance. 



Physical Chemistry of Surfaces. 



The subjects dealt with by Prof. F. G. Donnan, in 

 his address to Section B (Chemistry) are primipally 

 molecular orientation and molecular dimmsion^ at 

 surfaces and in surface films, molecular concentration 

 at surfaces and its effect on surface tension, electrical 

 potential differences at surfaces, stabilities of foams, 

 oil suspensions, lyophobic hydrosols, and oil emulsions. 

 The surfaces especially considered are the liquid-gas 

 and liquid-liquid surfaces. The researches of W. B. 

 Hardy have led to the conception of surface layers 

 of oriented molecules, as the result of unsymmetrical 

 fields of force surrounding molecules, due to the presence 

 of active atoms or atomic groups. The views of Hardy 

 have been confirmed by the work of W. D. Harkins 

 and his collaborators. 



The study of iinimolecular surface layers of insoluble 

 substances on the surface of water, initiated by the 

 late Lord Rayleigh and developed by H. Devaux and 

 A. Marcelin, has led in the hands of I. Langmuir and 

 N. K. Adam to the determination of molecular and 

 atomic dimensions. Certain recent investigations by 

 X-ray methods have an interesting bearing on these 

 results. 



Unimolecular layers may also be formed by the 

 adsorption of vapours on liquid and solid surfaces. 

 Dissolved substances which lower the surface tension 

 of a gas-hquid or liquid-liquid interface concentrate 

 at these interfaces. Do they form unimolecular layers ? 



Electric potential differences exist at the gas-liquid, 

 liquid -liquid, and solid -liquid interfaces. These 

 potential differences are affected by " surface-active " 

 substances, by ions, colloidal micelles, etc. The 

 potential differences determine the stabilities of oil 

 suspensions and lyophobic hydrosols. The " critical " 

 potential differences and the " critical zone " of potential 

 difference are of importance in such cases. 



The formation of concentrated surface layers and 

 surface films plays an important role in the production 

 and stabilisation of emulsions. Surface actions are 

 of importance in biological phenomena. The existence 



and :i( tivlfv iif till, llvin-' (ir^-nni^m are dynamic and 

 dep Mot in equilibrium. 



Th. ..,i>„.,.^...., I... ,.1. 



uill di pend on tl 



indiNidu ' .:''. I man iiic average ix-naviour ot 



" < roud 



The presidential address by Dr. Gertrud* 

 Section (' (Geology) is on the subject of " Iv. 

 I'ahiiint(il(C'\ :n Relation to tin- l.dv.tr l'al.ii//',;c 

 K<i( k^.■■ I! ' .....bl.-ins of the Lower ralati/"'' i' '^- 

 -till aw. .ire in the main those of 



tidii aiHi ii;.. I .il . >sliich are large!"- •■■*■--'• i^-iiuriu. 

 The Tiiii>t :>ati.-.lai lur) solution ap] ;e in the 



application of the principles of evolutK^naJ paiicontoloj/y. 

 The most effective modem cla.ssification of strata is 

 that ba^((l u]Hin the coming in of new forms of life, 

 but il il !.■> lo be of wide application this must not be 

 connected directly with < • r i^if 



the sedimentation. 



The variation in the nature of shallow-water faunas 

 due to various factors such as temperature, salinity, 

 and clearness of the water, is illustrated by reference 

 to the recent work at the Danish Biological Station ; 

 the ( 1 issiti( ation and correlation of such deposits 

 nui-t be a matter of great difficulty unless a common 

 l)nii( iple can be introduced. The standard for pur- 

 poses of classification must be sought in the faunas 

 of the deeper waters of the Lower Palaeozoic seas, 

 where the changes in the fauna show primarily as an 

 advance in the evolutional stage of the organisms 

 concerned. The various shallow -water deposits should 

 be referred to those of deeper-water origin when possible, 

 or the relative ages may to some extent be determined 

 by noting the evolutional stapc reached by various 

 organisms composing: the taiiiias. 



These principles are illustrated by a study of the 

 evolution of the Graptoloidea as the characteristic fauna 

 of the deeper-water sediments of the Lower Palaeozoic, 

 and it is shown that important evolutional stages are 

 characteristic of definite geological horizons, these 

 being recognisable without any knowledge of the 

 various Graptolite species. In the faunas of the 

 shallower-waters the evolution of certain features in 

 some species-groups of the Trilobita are described and 

 the horizons at which these occur are noted. Mention 

 is made of the work already published on other fossil 

 phyla, and attention is especially directed to that of 

 various observers on the evolution of the corals in 

 the Carboniferous as the type of work to be aimed at 

 in the future in the Lower Palaeozoic Rocks. 



The old purely descriptive work so often carried 

 out entirely in the museum or lat)oratory must give 

 place to that in which fossils are regarded as parts 

 of once-living entities possessing definite ancestors and 

 descendants developing alone detlnite lines, the relation- 

 ships of these being controlled always by field work. 



Zoology and its Human Aspects. 



Prof. Ashworth devoted the first part of his 

 address to Section D (Zoology), on September 13, to a 

 brief retrospective glance over some of the lines of 

 development in zoology since the last meeting in 



