292 



NATURE 



{July 26, 1888 



in its illuminative capacity, of the central body of our 

 system, are evidently illusory. The actual radiation of 

 the sun would be not improbably decupled by the sudden 

 change of its atmospheric and photospheric constitution 

 to that of Sirius or Vega. In other words, the stock of 

 energy now sufficing for the expenditure of ten million 

 years would then be dissipated in one million, with a 

 corresponding abridgment in time of the heating and 

 lighting efficacy thus vastly heightened in intensity. The 

 same caveat applies — should it be concluded that the 

 Sirian is a later than the solar stage — to attempts to 

 assign a term for the inevitable exhaustion of the 

 great fountain of vital possibilities. The objection is 

 however evaded by Prof. Langley's statement (p. 100) 

 that, at the present rate, " the sun's heat-supply is enough 

 to last for some such time as four or five million years 

 before it sensibly fails. It is certainly remarkable," he 

 adds, " that by the aid of our science man can look out 

 from this ' bank and shoal of time,' where his fleeting 

 existence is spent, not only back on the almost infinite 

 lapse of ages past, but that he can forecast with some sort 

 of assurance what is to happen in an almost infinitely 

 distant future, long after the human race itself will have 

 disappeared from its present home. But so it is, and we 

 may say— with something like awe at the meaning to 

 which science points — that the whole future radiation 

 cannot last so long as ten million years." 



Our author is sanguine as to the prospect of econo- 

 mically applying the sun's heat to mechanical purposes. 

 " From recent measures it appears that from every square 

 yard of the earth exposed perpendicularly to the sun's 

 rays, in the absence of an absorbing atmosphere, there 

 could be derived more than one-horse power, if the heat 

 were all converted into this use, and that even on such a 

 little' area as the island of Manhattan, or that occupied 

 by the city of London, the noontide heat is enough, could 

 it all be" utilized, to drive all the steam-engines in the 

 world" (p. in). No wonder that, enticed by such calcu- 

 lations, " practical men " should devote attention to this 

 unfathomable source of power ; and we may well believe, 

 with Prof. Langley, " that some of the greatest changes 

 which civilization has to bring may yet be due to such 

 investigations." 



" Future ages may see the seat of empire transferred 

 to regions of the earth now barren and desolated under 

 intense solar heat — countries, which for that very cause, 

 will not improbably become the seat of mechanical and 

 thence of political power. Whoever finds the way to 

 make industrially useful the vast sun-power now wasted 

 on the deserts of North Africa or the shores of the Red 

 Sea, will effect a greater change in men's affairs than any 

 conqueror in history has done ; for he will once more 

 people those waste places with the life that swarmed 

 there in the best days of Carthage and of old Egypt, but 

 under another civilization, where man shall no longer 

 worship the sun as a god, but shall have learned to make 

 it his servant." 



In his chapter on " Meteors," our author seems to view 

 with a certain degree of favour the suggestion that some 

 of these small bodies "may be the product of terrestrial 

 volcanoes in early epochs, when our planet was yet 

 glowing sunlike with its proper heat, and the forces of 

 Nature were more active " (p. 193). He does not, how- 

 ever, stop to discuss the difficulties besetting this 

 hypothesis ; had he done so, he could scarcely have 



failed to conclude them insuperable. The resistance 

 opposed by the atmosphere of the earth to the upward 

 flight of projectiles from its surface has, for instance, 

 never been sufficiently taken into account. It is quietly 

 assumed that some unspecified and insignificant addition 

 to the initial velocity needed to secure definitive escape 

 in a vacuum, would have sufficed to overcome atmo- 

 spheric hindrances ; whereas the minimum swiftness at 

 starting in the second case should be at least thrice, or 

 quadruple that in the first. The effectiveness of the air 

 in arresting motion is practically exemplified in the con- 

 tinuous meteoric bombardment against which it forms 

 our sole shield. Yet the projectiles composing it possess 

 far higher velocities than terrestrial volcanoes could, 

 under any conceivable circumstances, be supposed to 

 impart. And the few among them that meet the earth's 

 surface are impelled towards it by gravity after their own 

 movement has been wholly, or all but wholly destroyed. 

 Instances must be very rare in which an aerolite has 

 brought down with it in its fall any portion of its orbital 

 speed. Moreover, our present atmosphere is doubtless 

 rare and shallow compared with its pristine condition ; 

 while there is no certainty that volcanic action, of an 

 explosive kind, was ever much more enei'getic than it 

 now is. 



Prof. Langley adopts, or rather admits the " tempera- 

 ture-classification " of stellar objects current at the time 

 when his concluding chapter on " The Stars " was 

 written. It speaks volumes for the rapidity with which 

 the "new astronomy" progresses that, in a few short 

 months, this scheme — to which there were always serious 

 objections — should have fallen obsolete. Mr. Lockyer's 

 recent investigations have at least had the effect of 

 rendering a complete revision of ideas on the subject in- 

 dispensable. The book with which we are just now con- 

 cerned professes, however, not even to describe, but barely 

 to mention, the various departments, photometric, spectro- 

 scopic, and photographic, of stellar physical astronomy, 

 "on each of which," the author justly remarks (p. 248), 

 " as many books, rather than chapters, might be written, 

 to give only what is novel and of current interest. But 

 these," he adds, " are themselves but a part of the modern 

 work that has overturned or modified almost every con- 

 ception about the stellar universe which was familiar to 

 the last generation, or which perhaps we were taught in 

 our youth." 



An English edition of a work which we can recommend 

 as corresponding with singular felicity and charm to the 

 designs of the writer, is in preparation, and will shortly 

 appear. Some photographs of the moon, too recent to be 

 as yet generally known, will probably replace in it sue! 

 of Mr. Nasmyth's lunar illustrations as figure in the 

 American edition. A. M. Clerke. 



SOAPS AND CANDLES. 



Soaps and Candles. Edited by James Cameron, F.I.C. 

 Analyst in the Laboratory, Somerset House 

 "Churchill's Technological Hand-books." (London: 

 J. and A. Churchill, 1888.) 



THE object of this hand-book, as stated in the preface 

 is to add to the articles originally published ir 

 Cooley's " Cyclopaedia " additional information froir 



