♦ KNOWLEDGE 



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John GKEExnElD. If the snn's raj-s have been all these millions 

 on millions of years working their way round, and even now give 

 DO trace of oiming back, I fear I mnst ask you to wait till they do 

 begin to cfpmo buck before discussing your theory. Scioncc finds 

 whiit looks like ample reason for being certain that the solar rays, 

 or rather light-ondnlations, travel in constantly enlarging spheres 

 around the sun as centre. There is absolutely nothing known in 

 physics to suggest that this action can ever reverse its course. 

 There was no occasion to correct the spelling, the printers would 

 have done that if your letter had been marked for insertion; 

 but it could not be, except for Paradox Corner. — Xamuk. 1. 

 Draw throngh middle point, c, of AC, a perpendicular, cOD, which 

 will also be a diameter to the circle, being the centre. From 

 take on OD a length, OE, eqnal to Ac. Then EB, perp. to OD 

 will meet the circle in the required point D. 2. The highest point 

 of a primary is never so high as 45 degrees above the horizon. It 

 is highest when the sun is on the horizon, and it is then about 

 41 digrecR high. The higher the sun tho lower the rainbow, and 

 the fewer the degrees in its arc— Amatei-k desires to know tho 

 name, price, and publisher of best book giving chemical tests for 

 various substances.— L. J. P. Rodwell's Scientific Dictionary, price, 

 I think, 10s. 6d., gives modem scientific terms —J. II." Grant. 

 Tour description of Watfs parallel motion suggests that you are 

 considering a simpler form than the one I am familiar with. 

 Will you kindly send a sketch showing where C, C, ic., of your 

 dc oription arc situated ? You mnst not exjwct to find any way 

 of dm rmining a so that tho equation you have obtained shall bo 

 a.4 nearly as possible an equation of the first degree ; all yon can 

 do is to obtain an expression for tho deviation from the straight 

 when tlim is a maximum (that is, where x is greatest or least) and 

 then differentiating with respect to a determine for what value. Of 

 o this maximum deviation is least.— W. A. E. wants to know 

 whether alcohol in yeast, when made into bread, is destroyed in the 

 baking ? also if alcohol is to bo obtained from bread baked brown 

 by tie addition of pure water; and if so, whether excluding the air 

 would be a preventive.— H. B. Lino.say. 1 . Tho Kdinburqh Review is 

 decidedly wrong. Our English system of numeration reckons a bil- 

 bon OS (a million)', a trillion as (a million)' and so on— a very sen- 

 sible and uniform method. Americans use the unwise (and prncticiilly 

 absurd) plan of calling a thousand millions a billion, a thousand 

 billions a trillion, and so on. It would jiuzzle their arithmeticians to 

 explain how the hi-, tri-, and quadri-, Ac.,of those numbers pre to bo 

 wtcrpreted. 2. It is commonly supposed a French league is three 

 English miles ; but there are, in fact, two French leagues neither of 

 which is quite three miles in length, one of 2,000 toineg, or 242 

 English statute miles, which was formeriy the legal posting measure 

 the other the 25th part of a degree, or about 277 English miles! 

 The former is evidently inUiided by Flammarion in the passage 

 you refer to. Tlie English league is the 20th part of a degree, or 

 three nautical or geographical miles.— F. Craw.shaw. Letter for- 

 w»rd«I to publishers. English astronomers regard the day as 

 beginning at noon at Greenwich Aug. 3, 1 o'clock p.m., being 

 Aug. 3, 1 h. ; but Aug. 4 1 o'clock a.m., Iwing Aug. 3, 1.3 h. But 

 referring to civil, of course there must always be a question at any 

 placo neariy IH) degrees from ns, how the onlinary day that 

 ling should U- callwl— whether, for instance, at or near 

 I. Uh., a«tr<jn'.mical time, or noon of Ang. .'t, civil or mean 

 solar time at Grf.nwich the day which is near its commcncc- 

 mcDt .luill U- ™ll..d Augn.t 3 or 4. If wo pass eastwar.i from 

 OrccnwKh (tho earth being supposed to cease rotating for tho 

 moment) we find tl,e hoar earlier ami earlier in the morning till, 

 when we arrive at IWj east, it is midnight, and the morning hours 

 or Aug. 3 arc just aUot to begin. If wo go westward, wo find tho 

 time later and later in the afternoon till, when we arrive at l(-0' 

 west, which IS the same place we reache<l tho other way, it is mid- 

 night and the m/.ming hours of Aug. 4 are just about to iK-gin. 

 But f„r other longitudes wo meet with the same dinicolly. All wo 

 can ^y of the day at any placo is that it oveHaps the Greenwich 

 day of the same name by such and such a portion. Even at Paris 

 for example, there arc '.l\ minutes, when the day differs from 

 the (^eenwich day. Thus, from 11.50} in the evening of 

 Aug. 3 at Greenwich till midnight closing Aug. 3 at Greon- 



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wich, it is tl beginning of Aug. 4 at Paris. — W. Mkadow- 

 CKAKT. When you liuvo said that tho appio is in tho smaller 

 box, and the smaller box in tho larger, what more is there to siiy ? 

 —J. A. Oi.LARn. That seems about it. Besides, there is a certain 

 degree of probability that what tho mind regards as probable will 

 really occur.— J. Thomson. Do not know of Ling's book. No instru- 

 ment has yet been invented for measuring brain movements. As 

 trepanning would sooiii a necessary preliminary, I venture to pre- 

 dict that such nn instrument, when invented, will net bo widely 

 popular. — A. McD. 1. Dr. Ball refers to apponrances in tho 

 transit instruments, which inverts. 2. No : R.A. of a star is not the 

 time when tho star crosses tho meridian of a pliico; hut the interval 

 in time between the passages of tho meridian by (i.) the first point 

 of Aries and (ii.) the star. 3. You nio right in your correction of 

 what Dr. Ball says as to zenith dist + cnlat. being equal to polar 

 distnnce ; it should be colat. ± zenith distance, according as star 

 crosses meridian south or north of tho zenith.— A. Stradlino. .Most 

 willingly; not undcrtiiking, of course, to insert everything. — T. 

 CllASR Cox. Darwin attributes tho colours of human races to the 

 gradual influence of sexual selection. Slight difrerences at first 

 between different races were gradually increased. When the change 

 was in progress, there mnst have been, what is now not seen, a 

 marked difference of colour between the two soxes. As to tho lady 

 and gentleman you mention, scienco may express an opinion when 

 it has had evidence of their having existed. — E. Scott. Darwin 

 touches, in his " Descent of Man," on tho origin of the emotions, 

 feelings, conscience, &c. It is not very wonderful that wo have 

 but very vngue evidence on this point. You ask whether evolu- 

 tion recognisfS the human soul, and, if nothing can be destroyed, 

 what becomes of it alter tho death of tho body p I am not 

 concerned to say what evolutionists believe about tho soul, a 

 future life, and so forth. Theso matters Ho outside nur field 

 of inquiry ; but as to your question, regarded scientifically, 

 might it not be paralleled thus, — Scienco recognises tho human 

 mind ; nothing can bo destroyed ; what becomes of it after death ? 

 or thuf, Scienco recognises human strength ; nothing can bo 

 destroyed ; what becomes of our strength after death ? Scienco 

 con only recognise the strength, the mind and its powers, the soul 

 and its emotions, ns functions of the body. — Esckimador. Yon 

 must have been misinformed by tho person who stated that a book 

 giving the Latin roots (puro radicals) issued by the Clarendon 

 Press, was suppressed lost tho pupils should outleam tho teachers ! 

 — C. A. Wir.i.iAMsoN. Tho information was given in Knowledge 

 for August 4, p. 170. Publishers, Messrs. Trubner & Co., priuo 15s. 

 — J. Rawclifkk. Fear cannot find space for critique on Mr. 

 Whewell's article in Ji^urntd of Science, October, 1S80, on 

 "Free Forces in Nature." — J. Bedford. You are known. 

 — Faciebat. Before November wo shall have some papers 

 on meteors and shooting stars. Dropped K. because many 

 misunderstood.— F. J. M. Fear must nsk some reader with more 

 leisure than wo have to determine on what day tho full moon fell 

 in July, 157.1. — W. W. Fawcktt. In what way do Dr. Hermann's 

 assertions affect what I said ? Have I ever asserted there were no 

 cruel and wrong-headed vivisectionists ?— Z. Y. X. Many thanks. 

 We have sent on the electric boy to our electrical contributor for 

 his opinion.— tJ. Wii-son. We do not sec the ditliculty. It is certain 

 that ever since sub-aerial denudation has been in progress, every 

 formation must have been partially consumed to jirovido materials 

 for the next ; portions also would remain much as they were 

 originally formed. Why should you go on to reason as if 

 geologists asserted that "the whole of each formation was con- 

 sumed while the next was forming ? In so doing you make 

 the difliculty which troubles you.— H. Marriott. On tho hot- 

 test day you will often see cirrus clovds, which consist of 

 ice crystals. Whatever theory wo accept as to tho formation of 

 hailstones, we know (hat they arc formed where the air is at a tem- 

 perature below tho freezing-point. — J. Ralph. Yon have taken Mr. 

 Mattieu Williams somewhat too seriously; of course ho does not 

 really mean thnt drinking habits shonid bo encouraged in order to 

 get rid of the worse members of society. Besides, ho speaks only of 

 the coarser type of drunkards. Wo insert, however, as much of 

 your letter as wo can find space for. — A. H. Skf.lton. I noticed tho 

 two misprints at p. 170, 18S0 for 1800. There was only one wrong 

 in proof, and I corrected that, but somehow with tho result that 

 both were made wrong. It did, not, however, make tho answer 

 unintelligible ; for I received a note from tho querist thanking 

 mo for the rejily, which ho ha<l manifestly read as cor- 

 rected. So, ns tho answer had only been intended for him, 

 I did not think it worth while to correct tho mistake. 

 There was a very annoying erratum in No. 41, first page. 

 I had written that some regard "tho results of sound reason- 

 ing as if they were fanciful hypothesis." For " hypothesis," 

 I found " hypotheses," which I corrected. To my horror I found 

 the sentence altered into tho nngrammatical and onmcaning form 



