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 FOR GENERAL READERS. 



Vol. II. 



DECEMBER 21, 1888. 



No. 25. 



PAGE 



Scientific Table Talk 617 



Astronomy in China : The Pekin Ob- 

 servatory. {Illus.) 618 



Some Recently - Discovered Marine 



Crustacea. (Illus.) 620 



Memoranda 622 



General Notes 623 



Type-Writer. (Illus.) 625 



Natural History— 



On the Manners of Ants. (Ilhis,)... 627 



CONTENTS. 



PAGE 



Pisciculture 628 



Abstracts of Papers, Lectures, etc. — 



Physical Society 628 



Zoological Society of London ... 629 



Royal Horticultural Society 630 



Royal Meteorological Society ... 631 



Bristol Naturalists' Society 631 



Dundee Naturalists' Society 632 



Bournemouth Society of Natural 



Science 6j2 



Society of Chemical Industry 

 Liverpool Geological Society 



Flints 



Correspondence 



Recent Inventions 



Selected Books 



Diary for Next Week 



Sales and Exchanges ... 



Notices ... 



Meteorological Returns 



633 

 633 

 634 

 638 



639 

 640 

 640 

 640 

 640 

 640 



SCIENTIFIC TABLE TALK. 



By W. Mattieu Williams, F.R.A.S., F.C.S. 

 The structure of the interior of the earth is a much-vexed 

 question. Direct evidence, derived from penetration of 

 its crust in the operations of well-sinking, mining, etc., 

 shows that its temperature gradually increases as we pro- 

 ceed downwards, without presenting any indication of a 

 limit to such increase. On such data calculations have 

 been made, showing that at a very moderate depth, i.e., 

 moderate in relation to the dimensions of the earth, 

 materials such as compose its crust must exist in a state 

 of fusion, and therefore the earth, regarded as a whole, 

 is a fluid mass, encased in a solid crust the relative thick- 

 ness of which may be compared to that of the rind of 

 an orange as compared with the whole fruit. 



Opposed to this we have the speculative deductions 

 of certain mathematicians — Hopkins, Mallet, Sir W. 

 Thomson, Prof. G. H. Darwin— and others, who maintain, 

 on astronomical grounds, that the earth is solid through- 

 out, with a rigidity about equal to that of a globe of steel, 

 supposed also to be solid throughout. Hennesey, 

 Delaunay, Sir G. B. Airy, and others arrive at an 

 opposite conclusion, as a result of calculations based on 

 the same data. This is not at all surprising, considering 

 the refinement of the data, viz., the deformation of the 

 earth as indicated by its nutation, and the precession 

 of the equinoxes. 



The researches of W. Spring, which have been in 

 progress during the past eight or ten years, have rendered 

 us no longer dependent on these inverted pyramids of 

 complex calculations. He has proved by direct experi- 

 ment that the materials of which the earth's crust is 

 composed, when subjected to a compression correspond- 

 ing to that which they suffer at a few miles below the sur- 

 face/assume a fluid condition, and that this occurs at ordi- 

 nary temperatures, though, of course, it is aided by heat. 



He finds that lead filings, under a pressure of 2,000 

 atmospheres, unite into a firm block, which under the 

 microscope exhibits no trace of the original filings, but 

 presents all the appearances of a cast block ; that under 

 a pressure of 5,000 atmospheres the lead oozed out at 

 the joints of the apparatus. A mixture of filings of 

 bismuth, tin, and cadmium, in the proportion to form 

 Wood's fusible alloy, when similarly compressed, interfused 



with each other, forming the alloy, which melted at 

 158 Fahr., the mean melting-point of its constituents 

 being 468°. This shows true combination throughout. 

 Copper and zinc similarly treated produced brass ; 

 magnesium, zinc, bismuth, lead, silver, copper, tin, and 

 antimony, when mixed with sulphur and subjected to a 

 pressure of 6,500 atmospheres (97,500 lbs, to the square 

 inch), formedtruesulphides. In all these cases there was 

 an interflowingof substances usually described as solids. 



A similar fluidity is momentarily produced in opera- 

 tions of coining and die-sinking. The metal flows into 

 all the hollows of the die, as water would flow if poured 

 upon it. The water flows in obedience to the slight 

 pressure of its own weight, but the metal demands a 

 much greater pressure. This, as it appears to me, is the 

 essential difference between the two cases. Solidity and 

 fluidity are but relative terms. We know of nothing 

 that is absolutely rigid, nor of any absolutely fluid 

 matter, i.e., of no liquid nor gas that flows without some 

 degree of viscosity or internal friction. 



A pressure of 6,500 atmospheres corresponds to that 

 to which the material of the earth is subjected at about 

 80,000 feet depth below the surface, i.e., fifteen miles in 

 round numbers, or r ^ s part of the earth's diameter. On 

 a globe of one foot diameter this depth is proportionally 

 represented by a thickness of less than -^ part of an 

 inch, or that of a stout card, and yet there can be little 

 doubt that the combined action of the increased tem- 

 perature with the pressure must liquefy such materials as 

 those of which the crust of the earth is composed. 



Nevertheless, we need not be afraid of breaking through 

 this pellicle of rock-ice as we travel over it, for the 

 essential character of such fluidity, as Spring has demon- 

 strated, is that it is only manifested under enormous 

 pressure. Sir W. Thomson may possibly say that the 

 demand for such a shearing force to effect fluidity con- 

 stitutes a degree of rigidity corresponding to that of steel. 



In selecting such a substance as steel for his standard 

 of rigidity Sir W. Thomson has either intentionally or 

 inadvertently chosen about the most variable solid, as 

 regards rigidity, that exists. Its composition varies 

 from soft steel, containing 5 per cent, of carbon, to hard 

 crucible steel, running up to 3 per cent., or nine times as 

 much, its rigidity varying in similar proportion. More- 

 over, the same piece of steel varies through a still wider 



