NA TURE 



[Nov. 2, 18 



carbonic acid, some of them, such as calcium, magnesium, &c., 

 will form carbonates when the temperature sinks below that of 

 the dissociation of such compounds. The scoria thus formed 

 will float upon the heavy metals below and protect them from 

 cooling by resisting their radiation ; but if in the course of con- 

 traction of this crust, some fissures are formed reaching to the 

 melted metals below, the pressure of the floating solid will inject 

 the fluid metal upwards into these fissures to a height corre- 

 sponding to the floatation depth of the solid, and thus form 

 metallic vems permeating the lower strata of the crust. I need 

 scarcely add that this would rudely but fairly represent what we 

 know of the earth. 



But it may be objected that I only describe an imaginary ex- 

 periment. This is true as regards the whole of the materials 

 united in a single fusion. Nobody has yet produced so com- 

 plete a model with platinum and gold in the centre, and all the 

 other metals arranged in theoretical order, and with the oxidised, 

 silicated, and carbonated crust outside ; but with a limited 

 number of elements this has been done, is being done daily, on 

 a scale of sufficient magnitude amply to refute Sir William 

 Thomson's description of a fused earth solidifying from the 

 centre outwards. 



This refutation is to be seen in our blast furnaces, refining 

 furnaces, puddling furnaces, Bessemer ladles, steel melting pots, 

 cupels, foundry crucibles ; in fact, in almost every metallurgical 

 operation down to the simple fusion of lead or solder in a 

 plumber's ladle, with its familiar floating crust of dross or oxide. 

 As an example I will — on account of its simplicity — take the 

 open hearth finery, and the refining of pig iron. Here a metallic 

 mixture of iron, silicon, carbon, sulphur, &c., is simply fused 

 and exposed to the superficial action of atmospheric air. What 

 is the result ? 



Oxidation of the more oxidisable constituents takes place, and 

 these oxides at once arrange themselves according to their specific 

 gravities. The oxidised carbon torms atmospheric matter and 

 rises above all as carbonic acid, then the oxidised silicon being 

 lighter than the iron floats above that, and combines with any 

 aluminium or calcium that may have been in the pig, and with 

 some of the iron ; thus forming a siliceous crust closely resembling 

 the predominating material of the earth's crust. The cinder of 

 the blast furnace, which in like manner floats on the top of the 

 melted pig iron, resembles still more closely the prevailing rock- 

 matter of the earth, on account of the larger propoition, and the 

 varied compounds of earih-metals it contains. 



When the oxidation in the finery is carried far enough, the 

 melted material is tapped out into a rectangular basin or mould, 

 usually about 10 feet long and about 3 feet wide, where it 

 settles and cools. During this cooling the silica and silicates — 

 i.e., the rock-matter — separate from the metallic matter and 

 solidify on the surface as a thin crust, which behaves in a very 

 interesting and instructive manner. At first a mere skin is 

 formed. This gradually thickens, and as it thickens and cools 

 becomes corrugated into mountain chains and valleys much 

 higher and deeper, in proportion to the whole mass, than the 

 mountain chains and valleys of our planet. Aiter this crust has 

 thickened to a certain extent volcanic action commences. Rifts, 

 dykes, and faults are formed by the shrinkage of the metal 

 below and streams of lava are ejected. Here and there these 

 lava streams accumulate around their vent and form isolated 

 conical volcanic mountains with decided craters, from which the 

 eruption continues for some time. These volcanoes are relatively 

 far higher than Chimborazo. The magnitude of these actions 

 varies with the quality of the pig-iron. 



The open hearth finery is now but little used, but probably 

 some are to be seen at work occasionally in the neighbourhood 

 of Glasgow, and I am sure that Sir Wilham Thomson will find 

 a visit to one of them very interesting. Failing this he may 

 easily make an experiment by tapping into a good -sized "cinder 

 bogie," some melted pig-iron from a puddling furnace (taking it 

 just before the iron ' ' comes to nature "), and leaving the melted 

 mixture to cool slowly and undisturbed. 



For the volcanic phenomena alone he need simply watch what 

 occurs when in the ordinary course of puddling the cinder is run 

 into a large bogie and the bogie is left to cool standing upright. 

 I need scarcely add that these phenomena strikingly ilmstrate 

 and confirm Mr. Mallett's theory of earthquakes, volcanoes, 

 and mountain formation. 



In merely passing through an iron-making district one may 

 see the results of what 1 have called the volcanic action, by 

 simply obieiving the form of those oyster-shaped or cubical 

 blocks of cinder that are heaped in the vicinity of every blast 



furnace that has been at work for any time. Radial ridge 

 consolidated miniature lava streams are visible on the expc 

 face of nearly, if not quite all, of these. They were ejecte( 

 squeezed up from below while the mass was cooling, when 

 outer crust had consolidated but the inner portion still remai 

 liquid. Many of these are large enough and sufficiently ' 

 marked, to be visible from a railway carriage passing a cii 

 heap near the road. 



I intended to have made a few remarks upon another of 

 William Thomson's arguments for the earth's solidity, but 

 pressure of necessary business compels me to postpone them, 



W. Mattieu William 



Belmont, Twickenham, October 17 



Are We Drying Up ? 



In Nature, vol. xiv. p. 527, there is an article condei 

 from one by Prof. Whitney, with the alarming title "Are 

 Drying Up ? " with a number of facts to prove that we ai 

 that in the temperate zone at least, the supply of water in 

 rivers and lakes is failing at a more rapid rate than the dest 

 tion of forests will account for. 



Supposing this to be true, it can have only one of two cau 

 a decrease in the area of the ocean, from which the rivers 

 supplied through evaporation and rainfall ; or a diminutio 

 the supply of heat from the sun, which would of course dimi 

 evaporation. 



It is scarcely necessary to say that any perceptible decreai 

 the area of the ocean during historical time is theoretically i 

 improbable, and that practically there is no evidence of it, 



A diminution in the radiation of heat from the sun is not 

 possible : and it is also shown in the concluding paragrap 

 your article, that a diminution in the obliquity of the ecli 

 which I believe is now going on, must tend to diminish 

 supply of solar heat to the higher latitudes, and, conseque 

 to diminish evaporation and rainfall there. 



But were it true the supply of heat to the temperate zone 

 sensibly diminishing from either of these two causes, the fa 

 temperature would be quite as noticeable as the diminutic 

 rainfall ; and we should have proof of this from historical 

 dence as to the distribution of cultivated and wild plants, 

 there is no general evidence of the kind. In Iceland 

 Siberia, it is true, there appears to be some evidence ol 

 summers having become colder, but in the more temp 

 regions the range of cultivattd plants seems to have rema 

 unchanged, or at least not to have receded, from the ea: 

 periods of which we have any record. 



It appears, therefore, most likely that the diminution of 

 fall, where it really exists, is a merely local phenomenon. 



It seems to be forgotten, that while any local dimini 

 of rainfall is certain to give proof of itself in unfilled w 

 courses, any corresponding increase of rainfall in another lo< 

 will not prove itself in any equally visible way. 



There appears to be little doubt of the recent desiccatic 

 the region round the Caspian and Aral Seas, but it admi 

 being explained by a local cause. The Caspian has, wit hit 

 last few thousand years, been cut off by a geological change 

 the Black Sea or the Arctic Ocean, or from both ; since tl 

 has shrunk in consequence of the excess of evaporation over 

 fall, and the more its area has diminished, the less is the 

 fall of the surrounding regions. 



Some of the facts quoted, showing that rivers are ceasii 

 be navigable, do not necessarily prove that the rainfall is less 

 formerly, but only that the flow of the rivers is less regular 

 appears certain that the destruction of forests, and the intn 

 tion of agricultural drainage tend to this result, by throwini 

 water more rapidly off the land. But there is also a good 

 of evidence to show that the destruction of forests, and of ve 

 tion generally, tends to diminish rainfall. The most satisfa 

 instances, in every sense, are those of the converse kind, \ 

 show that rainfall may be increased by the judicious fosteri 

 vegetation. I will mention a few of these which occur t( 

 without being able to remember my authorities. 



In Lower Egypt, rain has become much commoner sine 

 formation of extensive date-tree plantations ; and the flc 

 water in the Kedron, in the neighbourhood of Jerusalen 

 become more abundant and regular since the planting of g 

 of mulberry and other trees about its sources. In the arid vol 

 Island of Ascension, where trees would not have lived, sh( 

 of rain have been attracted, by planting such herbaceous ] 

 as are best able to endure the almost permanent drought. 



