May 1, 1886.] 



♦ KNOWLEDGE ♦ 



209 



neir the shores i this striped rock does not appear to cover 

 the whole width of gi-eat seams i. 



It should be noted that the explanation of coal formation 

 above g^ven does not at all contradict the received conclu- 

 sions of geologists concerning the existence of swampy plains 

 upon which gi-ew the giant reeds, the tree-ferns, &c., found 

 in the coal measuies. These, according to my view, grew 

 upon the sedimentary plains corresponding to the sandy 

 plains, the or, on which the upper ends of the Norwegian 

 ^ords terminate, and which, under the climatic conditions 

 of the coal formation, would form just such plains as ai-e 

 ordinarily described. My only point of diffei-ence is that 

 the^e were not the gi-ounds upon which grew the scores or 

 hundreds of generations of trees which must be accumulated 

 in order to form a thick coal seam itself. That the con- 

 ditions under which a seam of coal containing only 1 or 

 2 per cent, of mineral matter to 98 or 09 of vegetable origin 

 was formed must be quite different from that in which was 

 formed a mineral rock in which the proportions are revereed, 

 98 or 99 minei-al to 1 of vegetable, is so obvious that it 

 seems almost a folly to insist upon it. Nevertheless it is 

 necessaiy to do so, as a mere inspection of the diagrams of 

 the " coal fossils " usually printed prove, and the fact that 

 most readers accept these as necessarily dispLiying the par- 

 ticular plants of which the coal itself is formed. If I am 

 right, the coal itself Wiis formed of trees and other vegeta- 

 tion of steep slopes ; while the fossil specimens of the coal- 

 measure rocks must consist of some of these isueh as would 

 be swept down during the deposit of the sediment i, and of 

 others of a very different character — viz., those which grew 

 upon the swamps that were formed when the deposit nearly 

 reached the water level. This reconciles the fact that we 

 tind conifera, which do not flouiish in swamps, side by side 

 with plants peculiar to swamps. 



A DEAD WORLD. 



Br RicHABD A. Proctok. 



IHE ancients fell into sti-angely incorrect ideas 

 about the heavenly bodies. They chose 

 the most beautiful of all the planets, beau- 

 tiful alike in symmetrj' of shape and 

 delicacy of colouring, as the emblem of 

 misery and gloom, regarding Siitui-day, 

 the day sacred to that planet god, as one 

 on which all work was unfortunate. They took, on the 

 contrary, the most disappointing and imsatisfactory of all 

 the sun's family, as a fortunate orb, the emblem of love ; 

 and although, strange to say, the day devoted to this planet 

 (Fiiday) also, was deemed unfortunate for beginning a gi-eat 

 work, or starting on a long journey, that was only because 

 the next day, devoted to the unlucky Saturn, compelled 

 rest ; and it is naturally unlucky to begin a great work if 

 in a few hours you will have to rest from it. 



In like manner the ancients looked at the full moon, and 

 Ijecause she was pale, and seemed so "silently and with so 

 wan a face " to climb the sky, they thought she was cold. 

 •' Ice-cold Dian " she seemed to them at the very time when 

 her sui'face, as modern science shows, is hotter a good deal 

 than boding water. I say this of the full moon in 

 perfect consciousness that an American physicist, Mr, 

 Langley, with an instrument which he calls the bolometer, 

 finds the full moon colder than ice. I reject the evidence 

 of that too delicate heat-measurer, and prefer the well- 

 attested teachings of the trustworthy old instrument, the 

 thermopile, whose work has been tested and measured again 

 and again and never found wanting in coiTectness. AVith 



too delicate a biilance, you do not always know what moves 

 it ; a breath may make some light substance you are 

 weighing seem twenty times as heavy, or as light, as it 

 really is. And so, I suspect, it ha;3 been ^vith Mr. 

 Langley's unpleasantly named heat-measuier. Some unob- 

 served change near at hand has made the bolometer tell of 

 cooling, where it should have told of heating if it had really 

 recorded the influence of the moon's beams. Once an 

 astronomer who supposed his delicate heat-measurements 

 were telling him of the heat of stars, found that in reality 

 he had been carefully measuring the heat generated by fiic- 

 tion as he turned his telescope towards the star. Mr. 

 Langley was making, we may be well assured, a similar 

 mistake. Of course he thoroughly believes in the results 

 he has obtained ; so fully does he beHeve in them that, 

 supposing the cold he has found in the full moon to result 

 from the thinness of the lunar air, or the absence of any 

 air on the moon, he adopted the belief that rock surfaces at 

 a great height above the sea-level do not get warm under 

 the sun's rays, as science asserts. It was on a lofty peak of 

 the Eocky Mountains, report says, that he maintained this 

 argument. " A priori reasoning," he said, " may seem to 

 show that these rocks ai-ound us must become hot under 

 the sun's rays, but science should trust more in d posteriori 

 evidence, the argument from observed facts," — here he sat 

 down, but for a singularly short time, on one of the rocks to 

 which he had refeiTed — " I — I stand to it," he is reported 

 to have continued, with some appearance of irritation, 

 " despite of arguments, a priori or — or otherwise — that the 

 moon must be intensely cold when she is full ; for my bolo- 

 meter sa\s so, and my bolometer is never mistaken." 



Sir .John Herschel had long since shown, by a process of 

 simple reasoning, that at the time of lunar- midday the 

 moon's surface must become at least as hot as boiling water. 

 The present Lord Rosse, using one of the fine telescopes 

 which his father constructed (not, ;is has been mistakenly 

 alleged, the great Pai-sonstown reflector *), an-ived at a 

 result corresponding to that which any one acquainted with 

 the laws of physics could have anticipated. He ingeniously 

 separated the heat which the moon reflects from the heat 

 which she i-adiates — that is, which she gives out as a warm 

 body ^viLl. He found that the siu-face of the moon at lunar 

 midda}- is 500 degrees hotter than the same suiface 

 at lunar midnight. (1 mean degrees Fahrenheit, of 

 course ; for the genei-al reader, however intimate he may be 

 rt-ith the rides for converting Centigrade or Pveaumur, pre- 

 fers to have no occasion to apply them.) Dividing these 

 equally — as is only fiiii- — on either side of nothing, we have 

 a range from 250 degi-ees below nought, or 282 degrees 

 below freezing, to 2.3U degrees above nought, or .38 degrees 

 above boiling : We may get less cold, by diN-iding un- 

 equally : but then we get so much the more heat, and that 

 would be quite unnecessary ; or we may get less heat, but 

 then we get so much the more cold, and 250 degi-ees below 

 zero would be cold enough in all conscience. The stoutest 

 among us would be killed by ten seconds of such cold, as 

 surely as he would be killed by one second in boiling water. 

 The moon, which passes through the whole range of this 



* " Along whose tube a tall man may walk witliont stooping," it 

 is the custom to add. Doubtless, for a tunnelling along which tall 

 men may walk conveniently, the great Eosse telescope is the best in 

 existence. But regarded simply as an " instrument for observing 

 the heavenly bodies," which perhaps is more nearly what it was 

 meant for, the " mighty mirror of Parsonstown " is cot so satis- 

 factory. If Sir William Herschel's great 40-feet telescope " bunched 

 a star into a cooked hat," Lord Rosses still larger instrument 

 played worse pranks still with the planets. " Zey show me some- 

 dings," said a well-known German astronomer, pathetically describing 

 his°experience at Parsonstown, " zey show me gomedings, and zey 

 say, ' He is Saturn ' .• and I beUece :em." 



