\N-. 13, 18S2.] 



* KNOWLEDGE ♦ 



•al and distinct, the red band being: nearest the sun. A band 

 • lute liRht descended from each spectrum half way to the 



on. These bands appeared slightly curved towards one 

 •her. The sun was shining through light, ill-defined, massy 

 Is. Fred. W. Foster. 



Distance, theoretically, about 22J° from the snn. — Ed.] 



SHAPE OF SATURN'S SHADOW. 



[200] — Is not the distorted shadow caused by the irregularity in 

 the density of Saturn's rings ? I offer this as a suggestion, because 

 I have frequently observed most eccentric forms thrown by a strong 

 light upon mist, totally out of drawing with the object causing the 

 shadow, — Yours, &c., F. Ybles. 



[The irregularity of the shadow may be partly due to this cause, 

 but cannot be wholly thus explained, as Mr. Ybles will see it he 

 considers that we see the shadow in nearly the same direction that 

 it is thrown. — Ed.] 



RING OF LIGHT ROUND MOON. 



[201] — Last night (Jan. 1), at 10.5 p.m., I and several others 

 saw a complete ring of light round the moon at a distance from her 

 of about twenty-six moons' diameters. The sky was somewhat 

 hazy at the time, and half-an-hour later was covered vrith heavy 

 clouds. If you can afford space for an explanation of this fact I 

 shall be much obliged. — Yours, &c., E. W. P. 



[What you saw was a lunar halo, caused by the refraction of 

 the lunar rays through ice crj'Stals. Y'ou nmst have considerably 

 under-estimated its apparent distance from the moon, which would 

 be nearer forty-two than twenty-six diameters of the moon.— Ed.] 



WINDMILL ILLUSION. 



Referring to the letter 161, p. 187, I dare say you will remember, 

 at Cambridge, another " illusion," whose discovery was ascribed to 

 Dr. Wheweil — viz., look from a point about a quarter of a mile 

 distant, edgeways, at the sails of a windmill in rotation, and you can 

 make them go whichever way you please. Thos. S. Bazley. 



[So also, if any one at some like distance whirls round a ball 

 attached to a string, the plane of the ball's motion being aslant, so 

 that the ball seems to describe an ellipse, it is difficult to tell which 

 way the ball is travelling, when the distance prevents na from seeing 

 whether it passes on the nearer or farther side of the swinger, when 

 lowest. — Ed.] 



RICHTER'S DREAM. 

 [202] — When lecturing at Sheffield in connection with the 

 Gilchrist Fund, you, on two occasions, concluded your lectures with 

 a splendid recitation about an angel taking a man through the 

 realms of space. Will you kindly inform me who is the author of 

 the poem, where I can obtain it, and — if it be not asking too much 

 — the price ? I have been told it is one of Jean Paul Richter's 

 "Rhapsodies," and have ordered it at my booksellers, but he could 

 not obtain it for me, though he tried for several weeks. I suppose 

 you would consider it too long to find a place in Knowledge. — 

 J. W. Staniforth. — [It is given in my book, " The Stars and the 

 Universe " (Longmans), also in Mitchell's " Stellar and Planetary 

 Worlds."— Ed.] 



POPULAR FALLACIES. 

 P! [203]— The letter of your correspondent " N." (No. 13C, page 

 188) affords the opportunity of suggesting that Knowledge might 

 advantageously publish an article or two on " Popular Fallacies," 

 with a view to the destruction of some of the many time-honoured 

 but baseless notions "which, handed down from generation to genera- 

 tion, even amongst the fairly educated classes, are accepted witliout 

 investigation, and believed in with the firmest faith. As examples, 

 I might point to the common practice of placing the poker cunningly 

 over a dull or dying tire, with the idea that "it will draw it up," 

 to the frequently expressed belief in the maleficent influence exer- 

 cised by the moon when " Ijing on its back " (whatever that may 

 mean) on the weather, &c. 



In the meantime, however, let me advise " N.'s " housemaid to 

 bestow as much care on her fire when the siin shines as when the 

 day is dark and cold, and she need not then fear its going out. I 

 am a pretty regular smoker myself, but I have never yet observed 

 niy cigar manifest a greater tendency to go out in sunshine than in 

 cloud. 



I suppose that the notion of the snn putting the fire out has 

 arisen from the fact that the brilliancy of the sun's rays overpowers 



the feeble light of the fire. Let " N." light an ordinary spirit lamp 

 in the sunshine. He will hardly see the flame at all. But if he 

 will put his finger where the flame should be, he will, I think, be 

 less inclined to believe that " bright sunlight interferes with 

 ordinary combustion " than ho now professes to be. — Yours, &c. 



Wm. H. a. 



GHOSTS. 



[204] — Referring to your article on this subject (p. 183, Dec. 30, 

 1881) with an extract from Dr. Wilson's work, may I ask if all the 

 ghosts, of whose appearance we have well authenticated accounts, 

 are to be accounted for on the principle of the '* physical derange- 

 ment " of the person who saw them r' How many ."iuch accounts 

 we have of persons seeing an iiidividual exactly at the time of his 

 death, though the said individual was miles away at the time, and 

 had not been thought about for years. Lord Brougham, for instance, 

 made an agreement when a young man at college with a friend, that 

 whichever died first should appear to the other, and very many 

 years aftewarda was startled by an apparition of his friend, just at 

 the time of his death. — Yours, &c., Ebenezeb Kelby. 



[205] — Will Professor Andrew Wilson kindly explain how he 

 reconciles the case of the War Office ghost with his disbelief in 

 ghosts ? In that case I think three friends in different parts of 

 England saw the deceased officer at the corrected date of his death 

 abroad. T. D. 



COMMUNICATION WITH THE MOON. 



[206] — I have seen it stated that a French philosopher suggested 

 the possibility of communicating with the inhabitants of the moon, if 

 such there were, by means of mathematical figures, constructed on 

 a very largo scale, in some such region as the Desert of Sahara, 

 Siberia, or the like. Can any readers of Knowledge give me in- 

 formation as to this idea, and the reasoning by which it was 

 supported? X. Datine. 



[Probably some reader may be able to answer "X. Davine's" 

 question. I have not myself seen the passage he refers to, but 

 believe it was a German, not a French writer, who suggested the 

 idea. |I find a passage in an old number of the Maijasin Piitoresque, 

 running as follows : — " If the Selenitos are beings endowed with 

 reason, men may establish a system of intellectual correspondence 

 with them. In fact, if the a.Tts and sciences are as much advanced 

 among them as they are amongst us, they must often have gazed on 

 the immense globe which shines in their firmament, having an ap- 

 parent surface sixteen times as great as that of the full moon as 



we see it. That globe is the earth on which we live They 



can see our rivers, ovir great lakes, our chief cities Thus, 



some gigantic telegraphic signal might be seen from the moon . . . 

 What signal should be employed ? to what language can we have 

 recourse ? All the signs by which we translate our thoughts are 



arbitrary and conventional How arc we to correspond with 



beings who, perhaps, have nothing in common with us but intelli- 

 gence ? Yet there is a method — the mathematical sciences furnish 

 it." The writer goes on to show that if the Selenites have 

 succeeded in constructing telescopes to sec such signals as we 

 might make, they must have also mastered tlie first principles 

 of mathematics. Among the fundamental propositions is one 

 due to Pvthagoras, called the theorem of the s(|uarc of the hypo- 

 thenuse (thiforeme du carrS de I'hypnthfnuse) " (viz., that the square 

 on the longest side of a right-angled triangle is e<iual to the sum 

 of the squares on the two shorter sides). He shows that if the 

 Selenites are mathematical at all, they must have discovered this 

 truth. "If, then," he proceeds, "we were to construct, as a 

 German geometrician has suggested, a figure illustrating this 

 theorem on a scale large enough to be seen by lunar telescopists, 

 they would understand its meaning, and would probably reply with 

 aiio'ther figure, or some other signal. Then wo should know that 

 inhabitants existed in the moon, and that they were endowed with 

 reason. Once this correspondence was started, who can say where 

 it would end i " Our author says he sees the smile of incredulity 

 on the lips of his readers. The idea must seem to them ridiculous. 

 and none wonder that it had its origin in a German brain. " But 

 do not judge too hastily : " the word impossible is hurtful to 

 human pride ; and if communication with beings in other worlds is 

 not impossible, it must be conducted in this way, for there is no 

 other. — Ed.] 



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