334 



NATURE 



[January 4, 191 2 



iidnptallon to pnrtirutnr purpose*, like high-«pf4Ki tooU or 



;iMiionr-plalr. This ha-* the incidrntnl but fnr-rfarhing 

 intlu'.trial ( on-;, li'i' m »• that workmen of great individual 

 <ikill in tlh i's are mut h less necfHsary now than 



(i>rni»Tl\. ^ !<« ncroinplished by bringing lempera- 



'. Murhanicnl control, and making them 



i>lr without the exfrrisp of critical 

 . ... i^.ij I of anyone. 



\ uiMi. intimate knowledge of the behaviour of the 

 iiwn. i..ls ihemselveii finds almost immediate industrial 

 .i|>t>li< aiiun. An industry which has grown to enormoun 

 piii|nirtions in recent years is the manufacture of Portland 

 . • int-nt, about which iittU- more has been known than that 

 I certain natural minerals were taken in thf proper pro- 

 l)»)rtion'« and heated in a peculiar furnace develop«'d by 

 ' .\p«'rience, the resulting product could be mixed with 

 water to form an artiticiai stone which has found extensive 

 ipplication in the building trades. Chemical analysis 

 Madily established the fact that the chief ingredients in a 

 -lUTfssful Portland cement were lime, alumina, and silica. 

 \\ ith a small admixture, p<'rhaps, of iron and magnesia ; 

 l>ul the relation in which these ingredients stood one to 

 iinother — that is, which of them were necessary and which 

 nwrely incidental — and in what compounds and what pro- 

 portions the necessary ingredients required to be present, 

 li;i» 111 ver been satisfactorily established. When we know 

 the stable compounds which lime, alumina, and silica can 

 combine to form, together with the conditions of equi- 

 librium between these for different temperatures and per- 

 centages of each component, a formula can be written 

 offhand for a successful Portland cement from given in- 

 gredients somewhat as an experienced cook might write 

 out the reci|ie for a successful dish. Such definite and 

 valuable knowledge is not beyond our reach. To obtain it 

 requires, in fact, precisely the same system of procedure 

 .IS that described above, which has already been success- 

 fully applied to many of the natural minerals repro- 

 duced and studied in the (ieophysical Laboratory during 

 the past five years. It happens that we have examined 

 a considerable number of these very mixtures in our 

 recent work upon the rocks. All the compounds of 

 lime, silica, and alumina have been established, and 

 a portion of the silica-magnesia series and their rela- 

 tions have been definitely determined throughout the entire 

 range of accessible temperatures. There is no reason to 

 apprehend serious difliculty in applying the same proce- 

 dure to the commercial ingredients of Portland cement, 

 and replacing the present rule-of-thumb methods and un- 

 certain products with dependable cements. The problem 

 of determining the relation of the ingredients in commercial 

 t ement and the conditions necessary for its successful 

 formation is exuiK the same in character as that of 

 determining th' i^ of formation of tli^ rn. l<s of 



the earth. 



\ physico-chemical investigation of the sulphide ores 

 over a wide raiige of temperatures and pressures has also 

 b«'en undertaken, which has developed a large body of 

 e.xact information of value in the mining industry. .\nd 

 such illustrations could be continued alnio-t ind- rtnitely if 

 it would serve any useful purpose to do ~ 



The industrial world is not, as a rule, ii in scien- 



tific principles ; the principle must first be narrowed down 

 to the scope of the industrial requirement before its useful- 

 ness is apparent. The immediate effect of an industrial 

 point of view is therefore to restrict investigation at the risk 

 of losing sight of underlying principles entirely. .An illus- 

 tration of this has come down to us through the pages of 

 history of a character to command and receive the utmost 

 respect, for such another can hardly be expected to occur. 

 We have honoured the early philosophers for their splendid 

 search after broad knowledge ; but in what is now the 

 field of chemistry, they allowed themselves to be turned 

 aside to the pursuit of a single, strictly utilitarian problem 

 — the transmutation of base metals into gold. The history 

 of chemistry is a history of this one problem from the 

 fourth to the sixteenth century — twelve centuries before a 

 nian arose whose broader point of view enabled him to 

 divert the fruitless search into other channels, from which 

 a science has slowly arisen which is now so broad as to 

 overlap most of the other sciences, and withal so practical 

 that scarcely an industry is entirely independent of it. 



Ihe so-called practical questions may therefore as well 



NO. 2201, VOL. 88] 



b« left to laki* care of th«ms«lv#». There has be«n no 

 lack of ingenuity in making profitable application of 

 jiyHtematic knowledge wh»'never the need for it l>ecame 

 in<ti«tent, for the rewards of such effort are considerable. 

 .And it i« no longer an argument again»t proc<-<-ding to 

 e»tabli<th relatitmship!. in a new field that the scope of their 

 application i aiumt l>" < ompletely foreseen. 



Now, what more promising questions occur to one than 

 these : If the earth w.is originally fluid, as it appear* to 

 have been, and has gradually cooled down to its present 

 state, its component minerals must at some time have be«'n 

 much more thoroughly mixed than now ; how Hid th^v 

 come to M-parate m the process of ccKiling int 

 individualised niasvs and groups as wf now f. 

 and what were the steps in their deposition / If t;. „, 

 earth was hot, whence came the marble of which we h.ive 

 so much and which can withstand no heat? What h.is 

 given us the valuable deposits of iron, of gold, of precious 

 stones? What determines the various crystal forms found 

 in the different minerals, and what is their relation? Some 

 must have formed under pressure, some without pressure, 

 some with the help of water, and some without. Where 

 is the centre, and what the source of energy in our 

 volcanoes? .All these questions, and many more, the geo- 

 physicist may attempt to answer. 



THE AGE OF THE EARTH.' 



'IllH doctrine of uniformity in geology stated by Hutton 

 in the words '* we find no vestige of a beginning and 

 no prospect of an end " was accepted by many until Lord 

 Kelvin surprised this school of geologists in 1868 by draw- 

 ing a very decided limit to the possible age of the earth. 



Lord Kelvin assumed that in the remote past the earth 

 was molten, and that it cooled down as a whole uniformly 

 until the crust just solidified. Then the earth's interior is 

 at a definite temperature (which we can now roughly esti- 

 mate from the melting point of the rocks of the crust), 

 while the surface has much the same temperature as now. 

 The rate of cooling is determined by the thermal con- 

 ductivity of the crust, i.e. by the rate at which the interior 

 heat can escape. 



It becomes possible to calculate what the temperature 

 gradient near the surface will be at any subsequent time, 

 or conversely, if we know the temperature gradient, to 

 calculate what time has elapsed since the crust solidified. 

 ^ By the age or antiquity of the earth I understand Lord 

 Kelvin means the time that has elapsed since the crust 

 solidified. The '' geological age " would be less than this. 

 The antiquity of a rock (or mineral) would only in the 

 case of the oldest rocks be the same as the geological 

 age. Thus the age of a mineral is a minimum • -timate 

 of the earth's age. 



The temperature gradient at a depth x and 



where 9^ is the initial surface temperature, K the con- 

 ductivity of tli'^ material of the earth. 



In applying this to the earth, we notice that .r is small 

 and / large, so that 



.All these quantities are known except t. Lord Kelvin's 

 estimates of the antiquity of the earth, using this method, 

 varied a good deal, but forty million years was the maxi- 

 mum he would admit latterly. 



-Sources of heat, the radio-active elements, are now 

 known which Lord Kelvin did not, of course, take into 

 account. The earth can no longer be regarded as a body 

 possessing only its sensible heat to supply the stream con- 

 tinually flowing from the interior to the surface — heat 

 which is, presumably, radiated into space. 



Lord Kelvin's treatment of the problem might be modified 

 by taking into account the additional supply of " radio- 

 active " heat. But the discoveries of radio-activity afford, 

 it appears to the writer, an alternative treatment of the 

 history of the earth which is more convincing. This treat- 



^ Portion of the presidential address delivered to Section .\, Australasian 

 Association for the .\dvancement of Science, 191 1, by Prof. T. H. Laby. 



