3 2 4 



NA TURE 



\_Feb. 5, i! 



all — he made anthropological observations, and collected ethno- 

 graphical objects. These are now in the Ethnographical Museum 

 in Florence, and illustrations of a considerable number of them 

 are found in his work. Besides these tribes, the book also deals 

 with the Bashkirs and Kirghises,_whom the author visited in 

 returning to Europe. 



The last Bulletin (No. 6) of the Geographical Society of 

 Belgium contains a paper by M. Oscar Royer describing his 

 journey on the Congo ; notes on a journey in Texas, by Mr. 

 Lancaster; also "Some words on Atlantis," by M. de Bloek, 

 who regards this fabulous region as merely one of those invented 

 by the ancients for the purpose of working out in imagination 

 their social and political theories. Finally, a study on the first 

 narrative of Columbus, and the old printed editions of it, with a 

 fac-simile of the first " Epistola C. Coloni," printed at Antwerp 

 in 1493. 



THE INSTITUTION OF MECHANICAL 

 ENGINEERS 

 T'HIS Institution held its annual general meeting in London 

 last week. The list of papers to be read we have already 

 given, though some of them were not read ; the only one call- 

 ing for special notice at our hands is that of Sir Frederick Abel 

 on a " P'inal Report bearing upon the Question of the Condition 

 in which Carbon exists in Steel." The following are the con- 

 clusions which Sir Frederick bases on the present and on the 

 two preceding reports : — 



" The results of the experimental work described appear to 

 warrant the following conclusions in regard to characteristics, 

 recognisable by chemical examination, which are exhibited by 

 different portions of one and the same sample of steel presenting 

 marked physical differences consequent upon their exposure to 

 the hardening, annealing, or tempering processes. 



(1) In annealed steel the carbon exists entirely, or nearly so, 

 in the form of a carbide of iron, if uniform composition (Fe.,C 

 or a multiple thereof), uniformly diffused through the mass of 

 metallic iron. 



" (2) The cold-rolled samples of steel examined were closely 

 similar in this respect to the annealed steel, doubtless because of 

 their having been annealed between the rollings. 



" (3) In hardened steel the sudden lowering of the temperature 

 from a high red heat appears to have the effect of preventing or 

 arresting the separation of the carbon, as a definite carbide, 

 from the mass of the iron in which it exists in combination ; its 

 condition in the metal being, at any rate mainly, the same as 

 when the steel is in a fused state. The presence of a small and 

 variable proportion of Fe t C in hardened steel is probably due 

 to the unavoidable and variable extent of imperfection, or want 

 of suddenness, of the hardening operation ; so that, in some 

 slight and variable degree, t'.ie change due to annealing takes 

 place prior to the fixing of the carbon by the hardening process. 



" (4) In tempered steel the condition of the carbon is inter- 

 mediate between that of hardened and of annealed steel. The 

 maintenance of hardened steel in a moderately heated state 

 causes a gradual separation (within the mass) of the carbide 

 molecules, the extent of which is regulated by the degree of 

 heating, so that the metal gradually approaches in character to 

 the annealed condition : but, even in the best result obtained 

 with blue-tempered steel, that approach, as indicated by the 

 proportion of separated carbide, is not more than about half-way 

 towards the condition of annealed steel. 



" (5) The carbide separated by chemical treatment from blue- 

 and straw-tempered steel has the same composition as that 

 obtained from annealed steel. 



" It does not appear that this inquiry can be further extended 

 with the prospect of obtaining any additional facts — elucidating 

 the condition of the carbon in steel exhibiting various physical 

 characteristics — the value of which would bear any proportion to 

 the very laborious nature of the necessary experimental work, 

 which has to be conducted with small quantities of material on 

 account of the necessity of carrying out the annealing, harden- 

 ing, and tempering processes with very thin pieces of steel. 



" I believe it will be admitted that, although the data obtained 

 have not led to the discovery of a ready chemical method of 

 differentiating between different degrees of temper in steel (a 

 method of examination which Prof. Hughes's interesting results 

 have almost rendered unnecessary), they have at any rate con- 

 tributed to the advancement of our knowledge of the nature of 

 steel." 



THE INFLUENCE OF DIRECT SUNLIGHT ON 

 VEGETATION 



""THE influence of direct sunlight on vegetation is generally 

 known, but surely deserves to be a subject of special study. 

 In the following paper we shall only endeavour to describe some 

 facts with relation to this influence. In the first place, the effect 

 of the sun's rays in the tropical regions will be traced, and after- 

 wards in the temperate and arctic zones. The constant high 

 temperature within the tropics is the cause of the plants being 

 less dependent on the direct solar heat than is the case in the 

 greater part of the temperate and cold zones, but, notwitstand- 

 ing this, there are plants even in the tropical regions requiring 

 for a luxuriant growth the direct rays of the sun. 



Of the tropical monocotyledonous plants, the palms are doubt- 

 less the most important, and of these the date-palm of the 

 Sahara Desert {P/ia-nix dactylifera, L.) furnishes daily food to 

 the inhabitants of this part of Africa. 



It is known that the subterranean wells are the only cause of 

 vegetation in this desert. When a well is discovered, in a short 

 time an oasis arises, and the date-palm appears. 



Considering that the first condition for the growth of palms is 

 a humid soil wherein the roots may vegetate, there seems to be 

 at first something strange in the fact of the Great Desert pro- 

 ducing species of this family ; but the Arabs say that this "Queen 

 of the Oasis " puts her feet in water and her head in the fire of 

 heaven ; and this is the cause of the rapid growth of the 

 plant (Greisbacb, " Die Vegetation der Erde," Theil ii. p. 87) ; 

 the water ascends by the roots into the tissue of the tree, and 

 communicates its temperature to the inner parts, so that the 

 influence of the sun's heat is tempered ; the evaporation of the 

 plant also causes a lower temperature ; thus it withstands a dif- 

 ference of gS° (from 126° to 28°), as occurs in the Desert 

 (Martins, " Le Sahara," Revue des deux Mimdes, 1864, vol. lii. 

 p. 613). 



Though, as we have said above, these plants require, in the 

 first place, water for their roots, the fact of the stems growing in 

 their wild state at a considerable distance the one from the other, 

 and never forming dense forests, proves that they require also 

 the light. 



But the date palm is indigenous to the Great Desert ; nowhere 

 else does this plant vegetate so rapidly. When cultivated 

 with success, it is also in a desert-climate, as, for instance, 

 in that of Murcia in Spain (the date forest of Elche), the high- 

 lands of Afghanistan, &c. The cause of its culture being with- 

 out fruits in the Mediterranean is the dry summer, there being 

 no subterranean wells, as is the case in the Sahara. 



The sugar-cane (Saccharum officinarum, L. ) is also a plant 

 requiring the direct solar light ; moist climates are disadvan- 

 tageous to its cultivation. Thus the climate of China, with its 

 heavy rains in May and June (Dove, " Klimatologische Beitriige," 

 vol. i. p. 102), but less precipitation in autumn, when the fruits 

 ripen, is suited for the culture of this plant. It is known that 

 the quantity of sugar depends on the quantity of sunshine. 



Turning to the warm temperate zone we see the species of 

 citrus cultivated in the sunny climate of Southern Italy, and 

 even by cultivation produce the delicious fruits generally known, 

 because they are in summer under the almost constant influence 

 of the sun's rays in open localities. In the Malayan Peninsula, 

 the supposed native country of these plants, they also grow in 

 open spaces and not in the jungles, requiring a moist soil, but 

 also the solar light, to ripen their fruits ; this explains why the 

 finest and largest oranges are obtained when the trees are trained 

 against walls, as is the case in some parts of Southern England. 

 The vine (Vitis vinifera, L. ) is also a plant requiring heat in 

 the after summer to ripen its fruits ; the climate of Southern 

 France and Italy is therefore well adapted for its cultivation. 

 In the continental climate of Bokhara in Turkestan (40° N. lat.), 

 with its hot summers (in the sandy desert on the Oxus River 

 the soil was found to have a temperature of 144° — Basiner, 

 " Reise durch die Kirgisensteppe nach Chiwa"), the plant is 

 cultivated in the open fields ; its winter covering is not taken 

 off before the end of March, but in April the temperature is 

 already very high, and in July it becomes insupportable; 1 the 

 fruit of the vine is ripe by the end of June or the beginning 

 of July. The soil is moistened here by artificial irrigation. A 



1 Mean temperature at Samarkand, lat. 39' 39', in 1881 : April 61°, May 

 70°, June 77 , July 8i°, August 77", September 68°, and December 28°; mean 

 temperature at 1 p.m. in June 86°, in July 93°, in August 92°, in September 



