28 



• KNOWLEDGE 



[Jan. 12, 1883. 



dPur paratrov Corner. 



A TIIKORY OF MERCURY. 



By Thomas Foster. 



{CoHfhiited from ptige 32.) 



IT was with a sense of ])leasure in the promise of future 

 less restricted play of fancy among men of science, that 

 I heard how a fellow of the Royal Astronomical Society, Mr. John 

 Brett — also kno>vTi as an eminent landscape-painter — had boldly 

 advanced the theory that the planet Venus, ne.\t neighbour to the 

 planet I am now (lealing with myself, is quite unlike the earth. 

 According to this theory, the planet which at this time is, I think, 

 adorning our morning skies (Mr. Proctor will confirm this, I believe), 

 has a polished metallic surface, enclosed within a crystalline or 

 vitreous envelope. This pretty jdanet, indeed, seems to be like 

 those mirror-globes which one sometimes sees in shop windows, 

 wherein you may see distorted images of yourself, of the people 

 walking past the window, of the epposite side of the street, and so 

 forth. I am not sure whether this theory may not in reality have 

 been entertained in very remote times. The ancients certainly knew 

 a number of matters the discovery of which we are too apt to attri- 

 bute to modern times. I have seen it stated — nay, proved, if the writer 

 who made the statement can be trusted — that the ancient Assyrian 

 astronomers knew all about the rings of Saturn, the four moons of 

 Jupiter, and other astronomical wonders which only the telescope 

 could have revealed to them. Now it certainly is a strange cir- 

 cumstance, in the light of Mr. Brett's attractive theory, that the 

 ancients should have associated the mirror mth the planet Venus. 

 In the very same plate, in fact, in which (in his " Saturn and its 

 System") Mr. R. A. Proctor shows an Assyrian picture of Saturn 

 inside a ring, there is shown, also, a figure of the Assyrian Venus, 

 Mylitta, holding in her hand what is manifestly intended to repre- 

 sent a mirror. And the mirror is a round one — no doubt, to repre- 

 sent a globe mirror. The race of astronomers who either found out, 

 or (if Professor Piazzi Smyth is right) had revealed to them, astro- 

 nomical facts regarded as the special glory of our own time, the 

 astronomers, or priests, who knew of the rings of Saturn and the 

 moons of Jupiter, might well have anticipated Mr. Brett in dis- 

 covering that Venus is a mirror-globe. 



I am aware that some astronomers have attempted to ridicule 

 this ingenious theory. They seem in the first place to assume that 

 because Mr. Brett is a most skilful painter, therefore he cannot 

 possibly be an able astronomer — " he paints like an angel," they 

 say (though I am not aware that either the painting or the writing 

 of angels has yet been made the subject of scientific observation), 

 but he " speaks " (about astronomy) " like poor poll,"* an assump- 

 tion manifestly unjust in the extreme. 



However, to my theory. It relates to the planet Mercury. Jlr. 

 Brett has told us all we could e.xpect to know (and more) about 

 one inferior planet ; let me endeavour to do the like for another — 

 leaving some one else to tell us all about Vulcan. 



Wlieu Mercury was last in transit. Professor Langley (of the 

 Alleghany Observatory, I beheve) made a carious observation. He 

 had found, in looking at the seemingly blackest part of sun-spots, 



* I would submit to the notice of the curious in such matters 

 (and especially to the consideration of some ingenious persons who, 

 a year or two ago, sought to show that the words " batten on this 

 ^loor," indicate the Ethiopic Moorish complexion of Hamlet's 

 objectionable uncle), the extreme probability — I would almost say 

 the certainty— that this saying of Johnson's has been entirely 

 altered from its original form. Badly as Goldsmith figured in con- 

 versation, it could hardly be said that he spoke like a parrot. But 

 if we remember that Johnson was a University man, and that Gold- 

 smith himself ought to have taken a University degree, the actual 

 expression employed by Johnson can easily he recognised. I suggest, 

 then, that he did not say of Goldsmith,"" He writes like an angel, 

 a,nd speaks like poor poll," but, " he writes like an angel and speaks 

 Uke a ' poll ' man," that is, like one who has taken a poll degree. 

 His courtesy led Johnson to overlook for the moment the fact that 

 Goldsmith had taken no degree at all ; or else he took it for granted 

 that if Goldsmith had taken a degree, it would have been onlv 

 among the poll men. For these, Johnson probably felt a wholly 

 unwarranted contempt, and Goldsmith's unsatisfactory verbal 

 utterances would seem to Johnson to correspond with what might 

 be expected from poll men. Besides, the contrast between an angel 

 and a man (of any sort) is natural and proper, whereas that be- 

 tween an angel and a parrot is forced, and even to some degree 

 irreverent. Johnson's careful avoidance of all that savoured of 

 irreverence is well known. This, by the way, if my theory is true, 

 is the earliest instance on record of the lise of the term " poll 



that a brilliant purple light is emitted, which, as seen through the 

 small pinhole he had left in the field of view, shone with all the 

 lustre of a purple star. This same method he applied to the 

 apjjarently black disc of Mercury in transit. Precisely the same 

 effect was produced. Obviously, then, the night side of Jlercury, 

 instead of being black, glows with a purple lustre. How is this H 

 Do we know of anything akin to this strange phenomenon — of an 

 uuilluminated surface, not intensely heated, shining with a purple 

 light? We do. The substance called " luminous paint" produces 

 just such an effect. Sulphide of calcium has been known ever 

 since 1768 (when Canton prepared it by heating a mixture of one 

 part of sulphur with three parts of calcined oyster-shells) to 

 be self-luminous for hours after it has been exposed to light. 

 The bones of cuttlefish and other substances will do. Electrical 

 discharges also will increase the brightness of this self-light. 



My theory, then, simply is that Mercury was once covered by 

 oceans, which have since — much Uke the moon's oceans — been with- 

 drawn into the interior, leaving a stratum of sea-shells, cuttle-fish 

 bones, &c., &c. Sulphurous emanations from the interior, and 

 electrical action exerted by the sun, supply all the rest that the 

 theory requires. Mercury is permanently coated with luminous 

 paint, naturally formed. The intense light of the sun by day 

 causes this luminous paint to glow with strong purple lustre all 

 through the night. Hence the brilliant purple star seen by Pro- 

 fessor Langley, when he examined the night side of Mercury 

 through a minute pinhole. 



Strange thoughts are suggested as to the past of a planet thus 

 seen to be strewn with the dihris of former marine life, in exceed- 

 ing wealth and in multitudinous forms. Strange 



[Very strange, no doubt ; but we must omit the rest of Mr. 

 Foster's rhapsodies until he has shown that Professor Langley's 

 blue-purple star was not the light of our ow7i sky. That light 

 was certainly shining through the pinhole. Might it not have 

 looked blue-purple, like the light of the sky when seen from lofty 

 mountain-tops ? But possibly Mr. Foster is jesting. — Ed.] 



(&UV iHatftfmatiral Column. 



NOTES ON EUCLID.— II. 

 (Continued from p. 15.) 



THE .Second Book of Euclid affords a good illustration of what 

 might be done in the way of simplifying Euclid, while re- 

 taining his arrangement of propositions, and scarcely departing 

 from his method. Thus this book might be presented as follows : — 

 Prop. I. — Enunciation and proof as in EucKd, — only, in a 

 simplified Euclid, the statement which now heads the demonstration 

 can be given as the enunciation, as in the props, which follow. 



Vrof.U.— Let a straight line AB be divided ^ ? ? 



A' 



B' 



into any two parts in the point C : then the 



rectangle AB, BC, together with the rectangle AB, AC, shcUlbe equal 

 to the square on AB. 



Let A'B' be equal to AB. Then by Prop. I., 



Eect. AC, A'B'-l-rect. BC, A'B'=rect. AB, A'B'; 



that is, rect. AC, AB-t-rect. BC, AB = sq. onAB. 



Prop. III. — Let a straight line AB be divided into any tv>o parts 

 in the point C: then the rect. AB,BC, shall be f' ? ? 



equal to the rect. AC, CB, together icith the sq. | , 



on BC. 



Let C'B' be equal to BC. Then by Prop. I., 



Rect. AB, B'C'=rect. AC, C'B' 4- rect. BC,B'C',- 



that is, rect. AB, BC = rect. AC, CB + sq. on BC. 



Prop. IV. — Let the straight line, AB, be divided into any two 

 parts in C : then the sq. on AJ8 shall be equal to the squares on AC, 

 CB, fngeiher loith twice the reef. AC, CB. 



A C B 



By Prop. II., Beet. AC, CB-l-sq. on AC = rect. AB, AC, 

 Rect. AC, CB-Hsq. on BC = rect. AB, BC, 

 .-. 2 Rect. AC, CB -t- sqs. on AC, BC =rect. AB, AC + rect. AB, BC, 



= sq. onAB (by Prop. II.). 



Cor. — If AB is bisected in C, the sq. on AB is equal to four times 

 the sq. on AC. 



Prop. V.—Let the straight line, AB, be divided into two eqital 

 parts in C, and into two unequal parts in D : then the rectangle, 

 .\D, DB, together xvith the sq. on CD, shall be equal to the sq. 

 on CB. 



i 



