346 



KNOWLEDGE 



[Oct. 20, 



anv answer which woul.l Ik- of us.; t» voii without .lopnitinit from 

 our iico'ssar)- rules.— YoiNc. Ciikmi>t. We cannot say which is the 

 best l>ook on Qiulitatire Chemical Analysis.— J. M. You ask for 

 mn imiwesibilitv. If one outline^of a Rarilen path is elliptical and 

 the path is of ttniform wi.itli. the other outline is not elliptical.— 

 IIallyabds. The strength of the Rainbaml only oorresi)onils in a 

 general way with the rainfall— K. W. R. See numbers 48 and 4il 

 for account of Raiuband observations.— J. MfNRo. Quito im- 

 poasible to ap|>oint meetiufrs to discuss manuscripts. — F. G.VHiiXER. 

 Pa|wn about Level Berths received. We do our level best, but our 

 subjects p't ahead of ns .-iometimcs (as the queen says). — .\. G. 

 H.kVXEs. We make the assumptions you refer to only in illustrating 

 the differvntial calculus, not to prove anything. — M.vi.colm 

 DoiGUts. You are quite right. The ii in the numerator of right 

 right hand fraction in lowest formula on pape 172. lirst col., 

 should be changed to 1 + :.— J. Fh.vskr. 1 believe there is 

 no known rule for determining the slip in the case of 

 screw-priipellers. — XE«-rox Ceo,s.sl.\xi>. The reasoning you have 

 used has been refute<l. Your mistakes are familiar ones. 

 I do not think your views have been refuted, in the sense in 

 which you probably use the wonls. When my friend Jlr. Dunkin 

 told yon he was unable to refute yuur views, ho no doubt meant 

 that he could not spare time to explain to yon their incorrectness. 

 I'aradoicrs labour under the erroneous idea that every holder of 

 other views is bound to correct their mistakes. — John Greenfield. 

 The earth's tilt is not caused by precession. I was right in.snyin(; 

 that the cause of it is not known. — • • • recommends hot Scotch 

 with a slice of lemon, to Mephisto. in preference to brandy. Docs 

 he recommend Three Star Whiskey? I fancy I recognise an old 

 acquaintance in Three Stars. — J. F. B. Yes, p. 258, col. 2, eight 

 lines from bottom, read "moon's" for "earth's." — B. Saxders. 

 Noticed the mi.sprint Truro for Tresco, but as no one would be 

 likely to imagine a lifeboat used at an inland place, it did not 

 seem' worth while to correct. — F. M.xckeitii. Many thanks 

 for notices of the American meeting. Will probably use some 

 after due digestion.— IcxoBAMls. I should say the less a lad of 

 sixteen or seventeen smoked the better. I dare say a half-bowl 

 of mild tobacco per day would do no harm, liut I am sure it 

 would do no good. Then, would he stop there ? -A Hiciilaxiier. 

 Perhaps some one who has had experience in the use of the Hain- 

 band spectroscope will give us a concise account 'of their e3tj)e- 

 rience.— Upsala. Now others very much like those papers. I am 

 one of those who do. The earth's orbit is an ellipse; but on the 

 scale of that picture you would not be able to tell it from a 

 circle. — SnoBTMAXi> Writer has taken no strong drinks for eight 

 years, nor has he felt the need of them. He therefore firmly bc- 

 iicves that " no man needs artificial stimulant- and strong drinks 

 are artificial." But is not our life artificial most of the time':' — II. 

 !*EBtlVAL. A bladder does not weigh the same when empty and 

 when distende<l with air; for, if distended with air, the air is at 

 greater pressure, and therefore of greater density than the sur- 

 rounding air. But if simply full of air, it of course weighs no more 

 when weighed in air. E<iually, an empty bladder and one full of 

 water are of equal weight if weighed in water. Hut a lilud<ler full 

 of air weighs more than an empty one by just the weight of the 

 air, when the balance is in a vacuum. — A. G. B. Kexxctt. What 

 you saw was a solar halo. The ice-particles in the air at about 22° 

 from the sun refracted the rays to the eye, each colour at its proper 

 distance from the sun. — .1. A. KobwiS wants a l)Ook on isomctrical 

 <lmwing and projection other than Sopwith's.— C. Uankix.sox. Wants 

 a cheap lxv>k on the blowpipe. — T. Such questions more suitable for 

 an edii<-5iti.mal journal.— T. M. Not quite suitable.— .K.STIICTE. (1) 

 A rniutieal mile is the sixtieth part of a degree. There are rather 

 more than 6'J laml miles in a degree. (2) I do not know how to 

 keep sunflowers fresh as long as pi.Hsiblc. By tho way, how do 

 \ .1 .K-thites keep NunHowers free fnmi earwigs? — W. U. Laxk. 

 • no one has yet measured accurately the distance at 

 ■innon-ball has' (nssed a man's head without killing him. 

 rvation would be rather a delicate one, 1 should imagine. 



ly six inches is the Imiit. 1 should Ijo content with as 



ia;.ny yards. — J. Kpii,i.er. We have scarcely so much available 



space as we had, bnt will find room if possible. — GbatefUI, is much 



[■leajted with Xatator's inntructions ; ho has " learned more," ho 



'■ frr.m his simple niles than frtjm all the books he has seen." 



I gratify Xatntor much. — J. H. Warii says his binder 



. in. Ixl. for binding volume I. " Moral " : Send next volume 



!■■• r.r ■■ binding." He advises Constant Reader to adver- 



-.- he did. He also tells J. Hitnmoek that Professor 



" Freedom of .Science in the Modern State," is 



r.iv at 2i.— Kxf Ki-sioB. Thanks. Soon.— E. T. C. 



■.vi'll one dnv be published. At presjrnt they are 



i r.L'ii,.- ;.il the time.— M,' E. L. The editor of KxowLEiXir. is 



rather i\itji'mn\ (it may l«c the result of some (tersonal prejudice) to 



recommend for the purpose yon mention, Mr. Proctor's work, now 



in the press, " The Stars in their Sonsons," republished from Kxow- 

 LEiHiK. For a first very sinqile guide, Mr. Proctor prepared " llall'- 

 hours with the Stars" ; for fuller information the maps which liavo 

 apjieared here ; for a knowledge of the quaint lore of the con- 

 stellations, and other such nnitlers, the " Easy Star Lessons." Each 

 work, however, is complete in itself. I believe the publisherH 

 propose to reprint Five of Clubs' Whist di8quisitiun.s, in tin' 

 form of au easy Guide to Whist, soon after they are conipleteil.- 

 Cins. WiTilAM. I thank you, and tho other subscribe is in wluis(' 

 name you write, very heartily.— C. S. You are quite right; the 

 previous predominance of heads in no way renders tho occurrence 

 of a run of tails likely. There is no tendency to exact equalisation, 

 only to equality of jiroportion. Thus, if there ai-o to bo a million 

 tossings, it is veiv m ';i.- '» :n,t. . , l.ntly, that there will be exactly 



500,IK.I0 heads niul : 1 it ii is also very unlikely that 



the ratio of heails i i . i ii r Ironi unity by more than one- 



thousandth part. Ill 111 \\ lil-, it is most probable that both 

 heads and tails will lie in niMi.l»r lietween Ullt.Tr.O and 500,250, but 

 very unlikely that tlicy will both be .'ilPO.OOO. Yot note that 

 500,000 is tho most iiroliiihle of all results— tho most probable, yet 

 verv unlikolv as compared with all other results taken together.- 



Leonard D. You are doubtless right, hut accuracy is secured by 

 the power of correction. You may notice, for instance, that thi' 

 Editor has recently not only corrected in those columns a mistakir 

 of his own, but published his correction elsewhere. This is, of 

 course, only right. There is not a particle of merit in doing 

 what it would bo very wrong to leave undone. But it wo all 

 agree to point out our errors or to accept readily tho corrections 

 of others when we recognise their correctness, wo cannot go very far 

 wrong. Why did not you send a letter with your corrections, for pub- 

 lication ? You may bo sure it would have found a place. — Nausea. I 

 doubt if there is "even any alleviation for sea-sickness. Y'ou may 

 prolong tho trouble by slightly diminishing it, but the totality of 

 misery is much the same. Yot remedy may bo found in attention 

 to the health before starting. If you take jolenty of exercise 

 for a fortnight, cat no pastry, little butter or cheese, and even 

 reduce your customary allt)wanco of milk, you will, if your 

 constitution is like mine, suffer much less than you other- 

 wise would. 1 have crossed tho Atlantic in misery for the 

 first five days on three occasions, and on three others without 

 a qualm from shore to shore, tho weather being rough all ^ 

 six times. — SolANUM. It is admitted toads are not venomous. — 

 J. Stevens. Thanks for Flint Jack extract.— W. B. Wicken. It is 

 chiefly because the temperance cause is injured by attacks on 

 the moderate, that there are to bo deprecated. If a Blue- 

 Kibbonist asks me whether I sympathise with his cause, my answer 

 is that I do most heartily ; but If ho fisks me to denounce moderate 

 drinking, and to assert, cnhir;n\ i i :.II .-.].iiienee, that most mode- 

 rate drinkers end bybecnii: i. li.i , I am obliged in common 

 honesty to tell him, " thilt ^ 1 . 1 ;iTi.>thcr colour" (Ameri- 



can version of our familari-a ,. i ^i i - itiiiKU. You want to know 

 too much nt once. But as yon liiiil from Victoria, I answer. 1. The 

 moon actually does rotate" on its axis once in each circuit around 

 the earth. (2) A diagram showing the moon's path for a year 

 should be about three yards across. We have not space for that. 

 (:}) The moons iif Jujiiter move rather differently from our moon, 

 their motions being more r.ipid, reliit Ivily, in their own orbits, and 

 Jupiter's less rapid in his. (4) Certainly; many comets travel 

 from star to star. (5) Given a passage through tho centre of the 

 earth (I am sure I liave no objection) and a body of the same 

 density to fall through, how far bevond the centre would it go, and 

 how long would it oscillatn i- Well, that would depend on the 

 rcsistanco of tho gases in the passage. If there were none, the 

 boily would oscillate through a whole diameter each way for ever. 

 — si oiT. It strikes mo Mr. Foster was joking when ho said, in his 

 article on Nature Mdhs, that Tom the Piper's Son was the 

 Thanimu/, of the solar myth. Perhaps Tom was. Perhaps, also, 

 the Swan into which the Ugly Duckling turned was afterwards 

 Ledii's Swan, and later, in partnership with Mr. Edgar, look a shop 

 in Piccadilly for the sale of articles of haberdashery to the Ledns 

 (I would say leaders) of fashion.— F. W. Mii.i.ett. It would bo 

 hopeless to attempt to determine tho true jiosition of tho 

 auroral streamers from such observul ions. U. Q. P. Yes, Carlyle's 

 statement is quite correct. Any motion brought about by mternal 

 react ions alters tho centre of gravity of tho system.- J. A. Westwood 

 Oliver. I think Boss and Smyth about right as to the destruction 

 of tho comet, but our earth is all right, I should imagine.— Alb. 

 Babbktt. 1 Ix-lievo' Aristotle was the first botanist whose works J 

 are extant. Only one would hardly call him a botanist, who e 

 so many subjects.— W. Pbobyn Nkvins. Yes, it is really too bad ( 

 liim to frighten all the other old women about tho mischief thej 

 cornet is to rlo the earth.— H'sETT. Do not know of any data 1 

 which lime taken to mak(! "pot-holes" can bo determined. — J 

 Macke.nzie wants to know the names of the authors of "ThoKo 



