oJO 



♦ KNOWLEDGE ♦ 



[JcsE 12, 1885. 



through the earth's atmosphere. That is, it mast have passed 

 through the earth's atmosphere at a level above the region where 

 clouds usually form. A. Cowper Kanyakd. 



THE PAST AXD FUTURE OF THE EARTH AXD MOON. 



[1745] — Without wishing to contradict the probability that onr 

 moon may have had an extraneous origin, as your correspondent, 

 "Hallyards," assumes in his letter (1712), may I ask does he 

 really believe that its first appearance in our system falls within 

 the traditional memory of man ? He quotes an old Greek myth to 

 the effect that the ancestors ot the Arcadians inhabited a moonless 

 earth, and considers the attempt to give a more rational explana- 

 tion of the Greek text as unsatisfactory. 



It is now generally admitted that the attraction of the moon is 

 the main cause in prodacing ocean tides. Geology gives us 

 numerous evidences of tidal action upon rocks aad stone far 

 anterior to the demonstrated age of man ; the cliffs near Tunbridge 

 \Yells and those on the Linfield road to Brighton are notable 

 instances ; yet these, no doubt, are comparatively modern when 

 compared with other formations. 



Since " Hallyards" has brought an ancient legend to support his 

 idea, by a legend let it be answered. Certain tribes of American 

 Indians have a tradition ■which tells us their early ancestors paid 

 occasional visits to the moon in times as remote (if the legend is 

 to be credited) as those of the moonless Arcadians. 



AYill your correspondent explain the difference between a com- 

 panion planet and a Satellite '; He says : — The moon is the only 

 " companion planet," but admits that there are numerous "satel- 

 lites." I have always understood that " planets " and " satellites " 

 were interchangeable terms. For instance, onr moon is onr atten- 

 dant " satellite," and it may be said of Jupiter and his moons, that 

 they form a "planetary " system of themselves. 



But to the more salient points of his letter. We are told that 

 the blue colour of the atmosphere is due to the water it contains. 

 This is a common enough supposition, but in my opinion none the 

 less erroneous. The maximum amount of aqueous vapour which 

 the air will hold in suspension, in the heat of summer, constitutes, 

 roughly, about, a fortieth of its entire weight ; the weight of the 

 atmosphere is only 15 lb. upon the square inch, equal to a column 

 of water .32 ft. high. By dividing 32 ft. by 40 we shall readily 

 see that the amount of aqueous vapour intervening between ns and 

 space would form considerably less than a foot of water, if con- 

 densed ; a foot of water will not give a blue colour (" Hallyards " 

 requires 16 ft.). Aqueous vapour intercepts light and gives opacity 

 to the air, but does not give it colour. The colour must be due to 

 either of its constituent gases. 5Iy individual opinion is that blue 

 is the characteristic colour of oxygen (" Hallyards" thinks oxygen 

 is red), just as chlorine is green, or bromine red. 



" Since oxygen gives redness to the blood, it may be oxygen that 

 makes Mars so very red." This argument is decidedly faulty. With 

 the exception of weight, the properties of a chemical compound 

 are not reflected upon its elements. If this is not clear to " Hall- 

 yards," let him take a solution ot iron-perchloride, and another 

 of potassic sulpho-cyanide ; both of these are destitute of colour, 

 but when mixed, a blood-red colour is produced. Each of the 

 elements in their compounds assumes a variety of colours. 



If we were to admit that the colour of Mars is due to an atmo- 

 sphere of oxygen, our own atmosphere would be nearly as red — 

 four-fifths of it being pure oxygen ; at the same time " Hallyards " 

 is content to believe that our earth would appear blue if viewed 

 from Mars. 



He speaks of "frozen" and "vaporised air" ; this, to a chemist, 

 is simply ridiculous, neither oxygen nor nitrogen is capable of 

 assuming such a form. 



He discredits the theory that the moon was once inhabited, 

 because he can see no trace of human work upon its surface. 



In a former passage he describes the persistency with which the 

 human race would cling to life upon a dying world ; the events 

 which he believes will occur upon the earth in future ages may 

 have already visited the moon, and the results, as seen upon its 

 disc, are quite compatible with what we should expect in the 

 decline of our ovm globe. 



Is it not evident that in the desperate effort to maintain such an 

 inclemeutal struggle — the death-struggle of our race — much, if not 

 all, of the relics of our former greatness would be demolished ? I 

 think so. If not, it matters little ; the destructive agents of the 

 atmosphere are ever at work. In our changeable climate their 

 ravages are too plainly discernible ; if this is the work of a few 

 centuries, what will occur in the extent of geological time yet to 

 come 'f The human race will pass away ; its very work will follow in 

 the dim vista, slowly ; but will the elements play their parts until 

 chaos come again ? ' Alex. Mackie. 



THE FLOATING DOME OF THE NICE OBSERVATORY. 



[1746] — It may be of interest to some of the readers of Know- 

 ledge to know that the immense dome intended for the Nice 

 Observatory will not float in pure water, as 1 have somewhere seen 

 it stated, but in a solution of chlomre of magnesium, which freezes 

 only at 40° below zero centigrade. The dome measures inside 

 22tn. 40, or 73 ft. 5| in., and will contain a very large refractor 

 of IS metres long, with an O.G. of 30 in. aperture, about receiving 

 its finishing touch by MM. Henry, of the Paris Observatory, who 

 has just finished their celebrated photographic refractor. 



It is to be hoped that the generous founder of this observatory 

 (M. Bischoffsheim) will still keep it independent of State super- 

 vision or intrigue, and not hand it over, as is stated his intention 

 is, to the French Government when once all is finished. 



Williams R. Kennax. 



INFINITE, GREAT AXD SMALL. 



l1747j — It was certainly Mr. Proctor who observed somewhere 

 obiter^ writing of space, " it cannot be infinite, for" — but then my 

 memory fails me. I took particular notice of so decided an opinion 

 put forth by so high an authority. 



I foresaw your comment on my remark that we cannot conceive 

 an3'thing less than a mathematical point ; and appreciate the colli- 

 sion between chemistry and mathematics. But what puzzles me is 

 such a question as this. Take a disk whose perimeter is a true 

 circle. The centre is a point. Can we conceive two ultimate 

 atoms (not superposed) each occupying the true centre, each eqtii- 

 distant from every part of the perimeter ? If not, I do not see 

 how an atom can be infinitely divisible ; i.e. Position seems to me 

 to collide, at last, with dimension. Hallyards. 



MATTER FOR REFLECTION. 



ri74S] — The " clock and mirror" puzzle seems to be only a new 

 view of our old friend, the "angle of incidence" and the "angle 

 of reflection." Observant reviewers know the perils which environ 

 the innocent lady-novelist who meddles with any " mirror " but her 

 own. The workings of the villain's countenance, and the trium- 

 phant hatred gleaming in his eyes, are watched by the hero, himself 

 screened from observation; behind a friendly door. Probably a less 

 obvious optical difficulty may find its solution in the same law. Not 

 only the eye of a portrait, but the painted line of moonlight on 

 water, appears to follow the spectator as he moves. " I can do it," 

 an artist once replied to my question, " but I cannot tell you how it 

 is done." Q. T. V. 



IS "IMMORTALITY" A FICTIOX ? 



[1749] — At one of the May Meetings it was stated that one chief 

 cause of the success of the Indian Mission was that '' delicate, 

 hic':hly-educated English ladies (magic word !) left all the comforts 

 of their English home for the work" — let us say, applying the 

 poet's heavenly language, to "dedicate their beauty to the sun" 

 (of Righteousness). 



Then yet a little while ago we saw a portent — Captains of the 

 Universities Eleven and Eight — going out to China, Bible in hand, 

 to proselytise. I could not help thinking, this is not fair ! Let 

 them at least take their Darwin in the other. (We know how the 

 Zulus gravel'd poor Bishop Colenso I) 



Nevertheless, though I argue thus, I cannot express my sense, 

 especially at times, of unfathomable (horizontally, without end), 

 dismal hopelessness — nay, despair — if we are to conclude, after all, 

 that the doctrine of immortality is all a farce ; that Cordelia is to 

 be hurried after a spasm of time into the hideous grave, to rot ! 

 Those homes of soul, her eyes (" heavenly orbs," indeed !) ; those 

 lips, too pure and royal to be kissed by the best and greatest 

 among men, to be gnaw'd and digested by worms 1 " Horrible, 

 horrible, horrible ! "* 



Yet the grMvitation of scientific opinion seems to tend to the 

 positive, absolute denial of immortality. Is not the prospect 

 almost appalling if this denial shall become the world belief (or 

 disbelief) ? What shall we do with our churches, our cathedrals, 

 all this world-wide fabric of Christianity ? 



Does it not seem that the doctrine of immortality — human 

 immortality, not the (undeniable) belief of the immortality of 

 the power of the I AM behind the masks of all— does it not seem 

 that this eternally comfortable doctrine, to us pilgrims and caravan- 

 journevers through the vale of tears is alone worthy of our cathe- 

 drals '/ You may say (I doubt vou, Mr. Editor, are of the novelist 

 George Eliot's opinion t), Let the churches and cathedrals become 



* Cheers for Cremation ! 



t Gaeas again. — Ed. 



