Oct. 27, 1882.] 



KNOV\^LEDGE • 



3G5 



anstofrs! to Corrrsponljfnts. 



All mmiKunicaficTit for Oit Edilor rrqximis early attention ihouU reach Ihe 

 ! «n or before the Sat-nrday {.receding the current i»»ui! o/Kkowlebob, the 

 irrulation ofvhich comjieh «» to go to prett early in the veek. 

 ' CoBBESPOjrDElCTS. — 1. iV'o queition* aelcing for icientifie iyformation 

 can be anevered through the pott. S Litteri lent to the Editor for correijiottdenf 

 cannot beforvarded, nor can the namee or addreesee of correspondent e he given in 

 anncer to private inquiries. 3. Correspondents should vrite on one aide or.li/ of the 

 paper, and put dravringa on a separate leaf 4. Each letter should have a title, and 

 in replying to a letter, r^erence should he made to its number, the page on vhich it 

 appears, and its title, 



W. Chai.mep.s ilAsTKES. Tour seeing two-thirds of a rainbow 

 was, it seems to me, a rather remarkable circumstance. — Tnos. 

 Walker. The paper on bicycle riding will be more suitable a little 

 later. The others on "How to Get Strong" shall be continued 

 more regularly. — W. Ackroyd. Mr. Grahame's question was pat 

 as for information, not as a foeman's whether worthy or unworthy 

 of cold steel. — Daleth. Quito impossible to answer definitely. 

 For most nebulfp we should recommend the lowest powers. — John 

 Gree.npield. You seem to hare singularly mixed ideas about 

 astronomical matters. If Jupiter were to fall into the sun there 

 would, I assure you, be a considerable disturbance. It is not the 

 case that the various planets are so going over, as you call it, as to 

 tilt. — Samsox. The writer of the papers on " How to Get Strong " 

 thinks the pulleys best about two feet apart. — Gkadatim. No; 

 there is no reason in the nature of things why the interval between 

 two periods of maximum glaciation should bo 21,000 years. The 

 variation of the eccentricity on which the change really depends 

 lias no such period. — Maui. A slight di6Rculty arises from the fact 

 that Venus is shown in both pictures midway between the horns of 

 the crescent moon. 



ilile and miles I've travelled. Sir, 

 Ten thousand miles and more, 



But Venus in that place, Sir, 

 I never, never saw. 

 B. M. It would lead to interminable discussion if attacks on Ency- 

 clopasdias were invited, as they would have been had we inserted 

 your letter. We fail to see any insult at page 302, certainly none 

 comparable to the gross insult commented on. There you and I 

 and all of us were touched. But then you may be one of those who 

 like to be insulted. There was a Frenchman who had been kicked 

 by the little Great Napoleon, to whom that application of imperial 

 boot-leather appeared ever after in the light of an honour! Men 

 are so differently constituted ! I .should have considered it a duty 

 I owed to the dignity of manhood to resent the insult at the time as 

 far as I could with just and reasonable regard to personal safety, 

 and ever after (unless apology were made) to speak of the attack 

 as a mean and cowardly action. If you recognise no duties iu 

 such matters, you yet should understand that others may. — C. 

 A. Edes. Mr. Erck is mistaken in supposing that the parabolic 

 orbit can be proved in tliat way by a single observation. — S. 

 or C. James. The answer was for another, whose letter was 

 not written on a post-card, but on a full sheet covering four 

 pages. I do not know where there is a large telescoiie the 

 owner of which could let you use it. Mr. De la Rue's photo- 

 glyphs of the moon are not, I believe, sold now. You can get 

 Itutherford's from Mr. Woodbury, and Ellis's from Mr. Browning. — 

 LoBESMlTH. Did the naughty printers call you " Lovesmith ^ " 

 They shan't do so any more. Now with regard to the effect of a 

 body as largo as the moon falling into tho sun, yon are quite mis- 

 taken. It can be shown that if the moon were to fall straight into 

 tho sun, the fall would generate as much heat as would correspond 

 with the sun's emission during more than a year. Suppose all this 

 extra heat poured out in a week. Then during that week, the 

 planets would receive about fifty times as much heat as they could 

 stand; at least our earth would.- — John Jones. Thanks for your 

 kindly note. There has been no intentional mystification. The 

 Editor of Knowledge and Mr. Proctor, Mr. R. A." Proctor, and Mr. 

 Richard A. Proctor arc, of course, one and tho same person. Yot 

 it is not an idle fancy or a mere joke which causes nio to speak at 

 one time as Editor, and at another in my own name. As Editor I 

 may have to ei])lain that some statement cannot be accepted, 

 which as Richard Proctor I would not take the trouble to contra- 

 dict. And in other cases there are differences. 1 believo, between 

 ourselves, that there never was any one less lit in his personal 

 capacity for tlie post of Editor than Mr. Proctor ; it pains him so 

 much to have to decline any communication or to contradict any 

 assertion, however rash. But duty comes in to give him strength. 

 —Another Perplexed Student. Tho difficulty arises from tho 

 circumstance that tho quantity under tho radical may bo taken 

 either positively or negatively ;" tho process of solution is blind to 

 this distinction. You get two answers, one soh-ing tho equation when 

 radical in numerator is taken negatively and the one in denumerator 



positively; the other solving it when these conditions are reversed. — 

 M. H. C. Pardon mo j I think it is quite correct to say that the 

 clouds, really straight bands, appear to the eye to bo curbed. You 

 saj- a straight band or line must always appear to the eye to be 

 straight. I assert, on tho contrary, that a straight lino always 

 appears to the eye to be part of a great circle of the optical sphere 

 or sphere of vision. Tho image on the retina is curved. You 

 draw a distinction between the effect on the mind and what appears 

 to the eye. Perhaps you can explain where tho difference lies. I 

 know of several periodicals which follow the example you refer to. 

 Suppose the one you specially refer to is Nature. — C. A. G. Have 

 not myself seen any later information of interest respecting the 

 silk moths than is given in Tyndall's " Dust and Disease." — 

 Romola. No ; we thank you. Nothing about Spiritualism in 

 Knowledge till we know something about Spiritualism. — Dazed, 

 G. J. 0\-ER, and Others. Question about tho heliographic messages 

 from Pyramids to Alexandria already dealt with ; see last number. 

 — E. B. W. Sound being something heard, I suppose it may be 

 fairly said that without cars there would be no sound. Without 

 matter no space, (or no matter what space). No matter or all 

 matter unchangeable, no time. Also, we have no time and no space 

 for such matter. — Tiios. E. Bon.'ser, Newton Ceosland, and 

 Others. We quite agree with you that the accepted modes of 

 drawing galloping horses are more true to natnre than the 

 views formed from the instantaneous photographs. One might as 

 well show cannon-balls in a battle picture over the soldiers' heads 

 as these absurd attitudes. They suggest rest instead of motion. 

 Want of space prevents our inserting your remarks. You will find 

 that similar views are expressed at p. 514 of Vol. I.; also in an 

 article by the Editor which appeared a few months since in the 

 Gentleman's Magazine. — J. Cram. I trust you are wrong about the 

 comet raising the sun's heat, at least in any great degree. — W. S. 

 Your theory about the apparent size of the rising or setting sun or 

 moon is quite untenable. The effect, due to irradiation, to which yon 

 refer, is well known and measurable. It cannot account for an appa- 

 rent increase many times greater.— J. E. W. Horn:. Thanks for your 

 pleasant note. Readers are practically unanimous about the 

 weather charts. C. J. B. points out (quite fairly) that it was rather 

 harden "the conductor at both ends of the house " mentioned at 

 p. 325, to expect it to do double duty. — An Oxford Graduate. You 

 would begin to feel warmer as soon as your distance from the snn 

 was perceptibly reduced. The air round yon might be very cold, 

 but believe me you wonld feel uncomfortably warm on the side turned 

 towards the sun. — J. J. Rubie. It might theoretically be so in the 

 case of perfectly elastic breathing apparatus. — Josn. Davidson. 

 I wish I knew the temperature of the sun ; I would in that case 

 tell you gladly. — W. Bolden asks if Nature's' light is visible 

 or invisible ? At a venture we should say it was visible. But 

 we liave only indistinct ideas of his meaning. — Lara. Let the 

 perps. CE and BD meet in O, and AOG be drawn to the third side. 

 Join ED. Then obviously, a circle will circumscribe ADOE : 

 wherefore angle EAO = angle EDO. But it is equally obvious timt a 

 circle will circumscribe BEDC ; wherefore angle EDB = angle ECB. 

 Therefore angle BAG = angle ECB = Comp. of EBC. Hence BGA 

 is a right angle. — S. Barker. We believe the writer of those articles 

 proposes to use Grecian models. We therefore return the photo- 

 graph yon have kindly sent us. — BRYfM wants a recent work on 

 British Mosses. — Z. Y. X. and Iota. Thanks. — J. P. Kirkmax. 

 Y'our problem requires diagrams. Will deal with it in our mathe- 

 matical column in our next, if possible. — Sirsikiher. Considering 

 that all the paper used daring several months past was provided at 

 the same time, you can hardly be right in asserting that tho paper 

 continually falls off in quality. 1 fear you notice every time a sheet 

 is a trifle inferior to the last, and do not notice when a sheet is 

 slightly superior to the last. It is, pcrhajw, natural enough, but 

 rather annoying, for the proprietors have far better reason than any 

 subscriber can have, to complain. — C. M. W. M. Suppose, first, 

 your wager of two to one against an honour at each cutting limited 

 to two. The possible events are four : — Plain, plain ; ])lain, honour; 

 honour, ])lain ; honour, honour. Results to you respectively, £2 ; 

 — CI; — £1;— £4. The chances of these events, ros]>octivelv, are 

 81 36 36 16 



VTi^, and :^^ ; therefore tho iniluc of your expectation 



169- leg- 

 is £2 



169' 



/81 _ jiO 32 \ 



\169~169~169/' 



or nearly 3s. Id. 



tation from a fair bet should be 

 of tho bet. Yon will find a sir 

 three, four, or more cuttings, 

 treating such cases. If you w( 

 of one honour, at least, in two 

 ns, or exactly 81 to 88, but i 



lolhiny, y< 



So that as your oxpco- 

 obviously have tho best 



It if you analyse cases of 

 That is the only sound way of 

 ro letting against the occurrence 

 trials, you would wngor less than 

 that case you would get nothing 



it either cutting gave a plain card, the other being an honour ; in 

 the case you suppose you got an offset for such cases. In the long 

 run you would bo snre to win at the o«ids you name.— J. H. W. L. 



