Feb. II, 1875 J 



NA TURE 



291 



on tlie constitution of the sun, has been led to form some views 

 of singular interest Ijearing on the probable structure of the crust 

 and nucleus of the earth. With his permission I am enabled to 

 lay before you some of the points in the inquiry he is now 

 pursuing. ' 



" Observation and theory have both led him to the unexpected 

 conclusion that in the case of an atmosphere of enormous height 

 and consisting of gases and of metallic elements in a gaseous 

 state, gravity overconnes diffusion, and the various vapours extend 

 to different heights, and so practically arrange themselves in 

 layers ; and that in the sun, where owing to the fierce solar tem- 

 perature the element", exist in such a state of vapour and of com- 

 plete dissociation, the known elements are observed to thin out 

 in the main in the following order ' : — 



Coronal Atmosphere . . . Cooler Hydrogen 



[ Incandescent Hydrogen. 

 Chromosphere ...,.< Magnesium. 

 ( Calcium. 

 / Sodium. 

 I Chromium. 



Reversing layer < Manganese. 



/ Iron. 

 ^ Nickel, &c. 

 " Mr. Lockyer suggests, and has communicated some evidence 

 to the Royal Society in support of his suggestion, that the metal- 

 loids or non-metaliic elements as a group lie outside the metallic 

 atmosphere. He also explains why under these conditions their 

 record among the Fraunhofer lines should be a feeble one. 

 Hence he considers that we have no argument against tlie pre- 

 sence of some quan'ity of the metalloids in the sun taken as a 

 whole, although that quantity may be small. 



" iMr. Lockyer then takes the observed facts together with the 

 hypothesis of the external position of the metalloids, and is 

 considering these two questions : — ■ 



1. Assuming the earth to have once been in the same con- 

 dition as the sun now is, what would be the chemical constitution 

 of its crust ? 



2. Assuming the solar nebula to have once existed as a nebu- 

 lous star at a temperature of complete dissociation, what would 

 be the chemical constitution of the planets thrown off as the 

 nebulosity contracted ? 



" It will be seen that there is a most intimate connection be- 

 tween these two inquiries ; the localisation of the various ele- 

 ments and the reduction of temperature acting in the same way 

 in both cases. 



" Thus to deal with the first question ; as the external gaseous 

 vapours (those of the metalloids) cooled they condensed and fell 

 (lU the underlying layer, where they entered into combination, 

 forming one set of binary compounds, and then others as the 

 temperature was reduced, until finally all the metals and earths 

 were precipitated. \ 



"It now we turn to the earth's crust we find it very gene- 

 rally assumed that the fundamental igneous rocks which under- 

 lie the sedimentary strata, and which formed originally the 

 outer laycr.s, may be divided into two great masses liolding 

 generally and on the whole a definite relation one to the other — 

 an upper one consisting of granite and other Plutonic rocks, 

 rich in silica, moderate in alumina, and poor in lime, iron, 

 and magnesia ; and of a lower mass of basaltic and volcanic 

 rocks of greater specific gravity, with silica in smaller pro- 

 portions, alumina in equal, and iron, lime, and magnesia in 



• Mr. Lockyer poiiits'out that this order is that of the old atomic or com- 

 bining weights, and not that of the modern atomic weights, as the-following 

 table shows : — 



Old Atomic New Atomic 



Weights. Weiglits. 



Hydrogen i 1 



Magnesium 12 24 



Calcium 20 40 



Sodium 23 23 



Chromium 26 52"S 



Manganese 27 ... ... 55 



Iron =8 56 



Nickel 29 58 



Aluminium does not find a place in the above list, because its order in the 

 layers has not yet been determined by observation, but the principle referred 

 to would place it between magnesium and calcium. 



t Firstly, those binary compounds capable of existing at a high tempera- 

 ture, such as the vapour of water, of hydrochloric acid, silica, carbonic acid, 

 and others would be formed ; secondly, the precipitation of these would give 

 rise to numerous reactions, forming a variety of silicates, chlorides, sulphates, 

 &c. ; thirdly, with the condensation of water the constitution of minerals 

 would be effected, double decompositioas would ensue, and the consolidation 

 of the outer shell commence. 



much larger proporlions, with also a great variety of other 

 elements as occasional constituents ; while the denser mstals are 

 in larger proportion in the more cen'ral portion of the nucleus. 

 The suggestion of Mr. Lockyer is that tliis order follows neces- 

 sarily from the original localisation of the earths and metals 

 before referred to, by which the oxygen, silicon, and other 

 metalbids formed, as they now do in the sun, an outer atmo- 

 sphere, succeeded by an inner one consisting in greater part of 

 the alkaline earths and alkalies, then by a lower one of iron ani 

 its associated group of metals, and finally by an inner nucleus 

 containing the other and denser metals. 



" As we have before observed, above nine-tenths of the earth's 

 crust consists of those elements which, on the assumption of the 

 external position of the metalloids, would constitu'e the outer 

 layers of the nebular mass. Thus, oxygen and silicon alone con- 

 stitute on the average ,Va of the mass of acid Plutonic rocks of 

 w liich the upper part of the first assumed shell of the earth con- 

 sists ; while beneath it are the basic rocks, into the composition 

 of which calcium, magnesium, and iron, combined with oxygen, 

 enter in the proportion of, say, ,"^,'u, the silica being less by i'm ; 

 still deeper lie the denser and harder metals, which reach the 

 surface only through the veins transversing the outer layers. 



" We next come to the second question dealing with the chemi- 

 cal constitution of the planets. It is imagined that the .same 

 consideration would hold good, and that the exterior planets may 

 approach in their constitution that of the sun's outer atmosphere, 

 and that the planets may become more metallic as their orbits 

 lie nearer the central portion of the nebula. Mr. Lockyer con- 

 siders that the low density and gigantic and highly absorbing 

 atmospheres of the outer planets accord with their being more 

 metalloidal ; and that, on the other hand, the high density and 

 comparatively small and feebly absorbing atmospheres of the 

 inner planets, points to a more intimate relation with the inner 

 layers of the original nebulous mass. For the same reason we 

 should expect to find the metalloids scarcer in the sun than in 

 the earth. 



" In the Jovian system, and in our own moon, we have a still 

 further support of the hypothesis in the fact that the density ot 

 the satellites is less than that of their primary. 



"I had hoped," Prof. Pi estwich continued, " to have brought 

 before you some of the results of the examination of the spectra 

 of portions of the outer igneous rock crust of the earth, which 

 Mr. Lockyer kindly undertook to compare with the solar spec- 

 Irum, but, owing to the state of the weather, the investigation 

 is not yet complete. It may, however, be slated that, as in the 

 spectrum of the sun, so in the spectra of the gi'anite, greenstone, 

 and lava already tested, no trace of metalloids is present, although 

 oxygen and silicon are so largely present in these rocks. 



" We can, however, still only look on these views as hypo- 

 thetical, but they commend themselves to us by their simplicity 

 and grandeur, and their high suggestiveness for future inquiry 

 and research. They show us also how the spectroscope may, as 

 the microscope has done already, aid the investigations of the 

 geologist — the one by endowing the eye with new powers of 

 bight with respect to tlie infinitely minute, and the other with 

 new powers of tangible analysis with respect to the infinitely 

 distant. 



"Quitting the eaily history of our globe, we leave the domain 

 of the astronomer and enter upon one shared by the geologist, 

 the mineralogist, the chemist, and the mathematician. Instead 

 of the sixty-four simple elements, their mutual reactions have 

 resulted in the formation of somewhere about 1,000 varieties of 

 rocks and minerals alone, with which tlie geologist has in future 

 to deal. He also has to deal with all the physical problems 

 arising from the consolidation of the crust of the earth — from 

 pressure due to gravitation and contraction — from the action of 

 subterranean forces — from the effects of heat — and with all the 

 varied phenomena resulting from these complex conditions." 



Mr. Prestwich then referred to the early belief that the thick- 

 ness of the crust of the earth does not now exceed thirty to sixty 

 miles ; and to the conclusion, supported by Sir W. Thomson, of 

 the late Mr. Hopkins, who, reasoning on phenomena connected 

 with precession or nutation, concluded that on the contrary it 

 could not be less than Soo miles thick or more. 



Remarking that it is difficult, however, to reconcile these views 

 with the extent and character of modern volcanic action, Prof. 

 Prtstwich referrei to the theories propounded by Mr. Mallet 

 in his remarkable paper recently published in the Transactions 

 of the Royal Society. 



" In stratigraphical geology," the lecturer went on to say, " the 

 great divisions originally marked out by our predecessors stand, 



