January 2, 1908 J 



NA TURE 



those shown in Fig. 3. Similar results are shown for 

 the Vvrnwy type dam. 



As a result of the first set of tests, the authors maintain 

 that, allowing for all irregularity in measurement and 

 material, there is no approach to linearity of normal stress 

 jp at least two-thirds, and probably up the whole height of 

 dams of current form. The mid-third rule is, therefore, 

 considered valueless as a stability test, and the success ol 

 engineers in building stable dams is attributed more tc 

 experience in choice of contours, and in the use of a large 

 factor of safety than to any validity in the method of 

 design. The complexity of the problem and the variations 

 of shear distribution led the authors to make a second 

 series of experiments, using many experimental refine- 

 ments. The general results were of the same character, 

 and an interesting set of curves is presented showing the 

 actual stresses in the Assuan dam as calculated from the 

 more refined measurements on the model. These curves, 

 like the preceding set, are rather irregular, and it is 

 difficult to believe that they can represent the variations 

 of stress in a body having any approach to homogeneity. 



Before concluding the memoir with some attempts at 

 semi-empirical determination of stresses, the following 

 processes are suggested for dealing practically with any 

 proposed design : — ■ 



'■ (i) Form a glycerin-gelatin white pigmented jelly 

 dam of the given contour. Determine the form and fixing 

 of the substratum to represent as closely as may be feasible 

 the local conditions. Rule the surface. 



" (2) Apply water pressure and determine by the methods 

 indicated above, using either a direct or optical micro- 

 goniometer, the shear distributions. .Ascertain the forms 

 of the horizontal and vertical section shear curves. 



" (3) Thence by integration — of course mechanical — find 

 the distribution of normal stress along one or two base 

 sections. From these deduce the stretches and squeezes, 

 and take as definite conditions of stability that the maxi- 

 mum stretch and squeeze shall be less than certain values 

 which may be effectively fixed by experiment." 



The authors then say that, with such a test, dams like 

 the Vyrnwy and Assuan are found to be theoretically 

 stable, whereas the mid-third rule gives only ail apparent 

 theoretical stability. 



We are grateful to the authors for their presentation 

 of the interesting results of such difficult experiments, and 

 hope that their work mav bear fruit. Their results must 

 stimulate discussion of a highly Important subject : but 

 we imagine that the day is not yet when the civil engineer 

 will proceed to the design of a masonry dam, as the 

 authors suggest, by " forming a glycerin-gelatin white 

 pigmented jelly of the given contour, and determining the 

 form and fixing of the substratum so as to represent as 

 closely as may be feasible the local conditions." Here, it 

 seems to us, there are added to the uncertainties of actual 

 conditions, .1 set of experimental processes liable to error 

 at many points. He will probably prefer to base a new 

 project on the designs of existing dams, modified as these 

 may be from time to time in the light of new ideas, and 

 perhaps by suggestions coming from work of the character 

 of that under review. E. Brown. 



THE ETHNOLOGY OF AFRICA. 

 T^HE communication by Dr. F. C. Shrubsall — " Notes 

 on some Bushman Crania and Bones' from the South 

 .African Museum, Cape Town " — issued as part v., vol. v., 

 of ■' .Annals of the South African Museum," In continu- 

 ation of a paper by the same author In the Journal of 

 the Royal Anthropological Institute for 1897, is an 

 important contribution to the ethnology of that region. 

 Incidentally, it marks a reaction against established 

 methods in anthropometry, which, particularly in the case 

 of mixed races, are now treated with well-merited 

 suspicion. In place of an induction founded upon a single 

 " index " derived from the study of the relative magnitude 

 of one skull dimension In terms per cent, of some other 

 dimension, the present paper is based on no less than 

 eighteen factors, and the figures have been subjected to 

 statistical investigation 01 ' 



NO. 1992, vol. 



the most modern lines. 



771 



The inquiry starts from a series, unfortunately limited! 

 in numbers, of skulls of the race known as the Strand- 

 loopers found In caves along the south-eastern seaboard. 

 These constitute a group more pure than that of the 

 Bushmen, and apparently quite distinct from that of the 

 Hottentots. The up-country Bushmen are intermediate 

 between the Strandloopers and the Hottentots. The latter, 

 again, present dimensions between the up-country Bush- 

 men and the Bantu, and in many characters they 

 approach the Negroes of British Central Africa more 

 closely than the Kafir tribes of the east coast. The 

 Central African Pigmies are by their prognathism clearly 

 removed from the Bushmen, and those of the forest zone 

 seem to be largely mixed with the Negro strain. Thus 

 the purest dwarf race is, or was recently, located on the 

 coast at the extreme south of the continent, the furthest 

 point to which, under pressure, they could retreat. 



Eastern and part of south-western Africa are occupied 

 by distinct races of Bantu speech, between whom, in 

 character as. well as in position, the Hottentots seem to be 

 intermediate. Quite distinct from these races already 

 mentioned are the Somalis and Gallas, of whose 

 physical character little is known. The Masai further 

 south may be allied to these, but they are quite distinct 

 from the Bantu-speaking Negroes. The West African 

 Bantus, between the Rio del Rey and the Congo, in some 

 respects resemble the eastern tribes of the same stock, in 

 others approximate to the Pigmies. 



The race history of South Africa may thus be re- 

 constructed — the first inhabitants were of the Bushman 

 tvpe. Round the great lakes and in the Upper Nile 

 vallev the tall Negro tribes were developed, or at least 

 are found in occupation of this region. Pressure from the 

 east drove a large section of these southwards, and these 

 in their turn pressed the Bushmen partly to the extreme 

 southern coast, partly into the forest zone, where they 

 intermingled with their neighbours. Some of the Negroes, 

 again, passed north of the forest tract towards the Atlantic 

 shores, and under pressure of tribes from across the 

 Sahara were in part driven back to the forest, arid in 

 part down to the western sea, where in an unsuitable 

 environment their physique deteriorated. Some of these 

 Negroes mav have been forced down the Nile valley, taking 

 with them or driving before them any survivors of the 

 northern Bush races, who thus came into contact with 

 Egypt : or, as an alternative, it is not impossible that the 

 range of the Bush peoples may have previously extended 

 much further to the north than is usually supposed. 



These conclusions rest, as we have said, on a com- 

 parativelv small number of skulls. It is to be hoped^ that 

 a fuller supplv of African crania may soon be available 

 bv which these interesting speculations may be more 

 adequately tested. 



THE PLACE OF THE LABORATORY IN THE 

 TRAINING OF ENGINEERS^ 



IT is now generally conceded that the advancement and 

 prosperity of an engineering establishment depend 

 upon the number of well-trained employees it possesses, 

 but much difference of opinion exists as to whether the 

 education given in our engineering colleges is of the kmd 

 best fitted to produce the type of man who will be of real 

 value to his firm. 



As a rule, at the present day, a boy who mtends to 

 become an engineer, on leaving school takes up a three 

 or four years' course at an engineering college. Oti. 

 leaving college he will be found to have a fair theoretical 

 knowledge of engineering, to be capable of makinga draw- 

 ing, of testing specimens of materials, of taking indicator 

 cards, and, generally, of carrying on an ordinary engineor 

 boiler trial. As a rule, however, he is Incapable of making 

 much practical use of his scientific knowledge, and if 

 compelled to act on his own responsibility in the case of 

 some mechanical problem often fails badly. Many 

 employers thus look coldlv on a system of education which 

 produces such poor results, and we have here an explan- 



1 B.ised upon a paper read before the Innilution of Engineers and Ship- 

 builders in Scotland, by Prof. A. L. Mellanby. 



