774 



NATURE 



[November 24. 1923 



one is 8tru< fact that the jun« • • vstal 



to crystal i - y:ion of weaknesK, i fact 



the strong. tal aggregiiit;. Metals, 



when forcil cold, normally break 



through the crystal i ;ili>iu: tin- juintions 



There are a large "t (■\i.<-i:iiiriit.il i.uts 



supporting the view mat the gap between two 

 adjacent kittices is bridged by a region of irregularly 

 arrangi ' • n stituting a layer of amorphous 



materi. strength. 



FinallN, "'.,.. nlul solnfions wf find that the 



interatomic <lisl. 111! I ., ilniii!:Ii \.n\in!i ;i t-w percent.. 

 arc roughly con i.n! : ■ ! i.imm.I mtermetailic 

 coinponnds the mti : are .sometimes 



greatlv reduced. I i i, the distance 



IS of ill!' niilcr i»f 1 I'lii in the com|X)und 



Cu.Al,, .iliinuniuni .:■ timiifl witli a centre 



distance ot (mi1\ :.-.\z .\.\ . In tin> i .isc, therefore, 

 the nature ot tin- inter. itoniK liindiiif,' imisl In- (juite 

 (liderrnt, ;iiul tlii^ probalilx' constitute-- the real 

 (lilleifiuc lie(v\een a ((uuixjuihI and a sohd sohilion. 



I "I \..\.( .riihtli. who followed, pointed out that while 

 .it tii-^i smht tlie (orrelation of data on the breaking 

 strenL'ths ot inat( ri.iK with the magnitude of cohesive 

 fon e^ (len\((l 1>\ ]ili\Mcal method should be com- 

 par.itively simpU', this is f.ir frnui liein^ the case. One 

 reasMii for this is that the majority of structural 

 metals are ductile, so that under ordinary stress 

 systems, which almost m variably comprise shearing 

 stresses, the primary failure of the specimen does 

 not involve atonin separation at all but is a failure 

 in shear. Kow the mode of collapse of a space-lattice 

 in shear is a subject which has been studied very 

 little by physicists, so that practically no information 

 from the point of view of molecular cohesion is avail- 

 able to engineers. 



In the case of certain materials, for example, 

 glass, stone, and hard steel, which exhibit brittle 

 u"actures running perpendicular to the direction of 

 the greatest tensile stress, some progress in the subject 

 has been made. Calculations show that in such 

 cases the obser\'ed tensile strength is only a small 

 fraction of the calculated molecular tenacity. This 

 discrepancy may be avoided if one assumes the 

 existence of minute cracks in the material fracture 

 being due to the very severe concentration of stress 

 at the comers of the cracks. A formula may be 

 developed which gives results of the right order of 



magii ' 'he radius of the corners of the crac v. 



is taK •> or three molecular 8paciii|[s. The; 



is another type of fracture obtainetl with briti 

 materials, namely, cracks running obliquely to t 

 principal stresses, the best known cas<r ' 

 rushing fracture obtained by simple c> 

 Ihjs may be treated in a somewhat simii.u ni.m! 

 by the assumption of a large number of minu 

 cracks oriented at ran<lom in the material. 



With regard to the hieakdown of ductile metiil 

 Dr. Griffith and Mr. L<jekiipei.scr have worked o' 

 a theory of plastic strain in which the conclusion 

 reached that plastir strain i.s simply the extern 

 manifestation of pi i,'es occurring within the 



material. This vii elf is not new, hut th- 



novelty arises from the fact that ded' 

 made regarding tlie number and nature of ; 

 phases concerned in the The qucbiiuu an 



whether it is likely on j grounds that ph.t 



changes can occur as a rci>ult of the application of 

 shear stress ; given that this is so, the evidenc«» 

 more in favour of a resultant change in r- ' 

 orientation of the atoms than of their configur, 



I'rof. Lindemann considered that the .. 

 made by previous speakers that atoms o: 

 are either bonded together, ornot Iwnded, Is pi ema 1 1. 

 and cited the fact that fairlv definite evidence f 

 intramolecular attraction without definite bonds 

 to be found in the Sutherland correction to t: 

 temperature coefficient of the viscosity of gase 

 derived by assuming mutual attraction of molecul 

 and verified experimentally. 



Prof. R. W. Wood mentioned an interesti: 

 experiment reiiuiring explanation. A crystal of ro 

 salt placed in hot water can be immediately bent ! 

 the fingers, and remains deformed when removed frci 

 the water. The range of temperature over whi' 

 this has been observed is small and the phenomena 

 does not occur in the case of immersion in hot oil. 



To sum up, the discussion brought out clearly the 

 fact that we are still only at the beginning of a com- 

 plete explanation of the general phenomena, and 

 there was point in the somewhat facetious remarl: 

 of Sir Oliver Lodge that it was an extraordinary^ fa 

 that, after all these years, three important sectio: 

 of the British Association should be gathered togeth- 

 to discuss why, when one end of a stick is raised froiu 

 a table, the rest of it also comes up. 



Paris Meeting of the International Council for the Exploration of the Sea. 



TPHE sixteenth annual meeting of the International 

 ■•• Council for the Exploration of the Sea was held 

 in Paris, on the invitation of the French Government, 

 on October 1-5. By the courtesy of the Administra- 

 tive Council, accommodation was provided for the 

 Council in the Inslitut Oc^anographique, founded 

 by the late Prince Albert of Monaco. The following 

 countries, members of the Council, were represented : 

 Belgium, Denmark, Esthonia (for the first time), 

 Finland, France, Great Britain, Holland, Norway, 

 Portugal and Sweden. Representatives of the Irish 

 Free State attended as visitors. 



The usual committees and sections for hydrography, 



f)lankton, statistics, herring, plaice, cod and haddock, 

 imnology, the Baltic Sea and the Atlantic Slope were 

 assembled, and a new committee, named the North 

 Atlantic Committee, was formed. 



It is important to observe that all committees and 

 sections are now instructed to formulate precise 

 programmes of work, allotting to each countrv con- 

 cerned a definite part in the programme, which it 

 undertakes to perform. Each country' is called upon 

 afterwards to report to the Council on the work it has 



NO. 2821, VOL, 112] 



carried out in accordance with these undertaking- 

 and the effect of these reports is embodied in a genera; 

 progress report subinittcvl to the Council at each 

 meeting. The tendency to present excellent but un- 

 realisable recommendations is thus discouraged. 



For the most part the committees reafl&rmed their 

 existing programmes m respect of which generall\ 

 satisfactory progress wa^ reported. It will be 

 observed that there are three committees for tie 

 study of particular fishes. The Plaice Committee, 

 the recommendations of which for the protection of 

 the plaice fisheries were adopted by the Council in 

 1922, and are now under the consideration of the 

 participating Governments, is chiefly engaged in 

 watching developments and checkin-.; its own con- 

 clusions. 



The intensive investigations of the plaice having 

 thus come to a pause, the study of the herring, cod 

 and haddock is being vigorously prosecuted, in accord- 

 ance with comprehensive practical programmes 

 adopted in 1021, and afterwards modified in the light 

 of experience. I'nfortunately, owing to the difi&culties 

 of the time, many of the countries concerned are 



