184 



• KNOWLEDGE 



[July 21, 1882.. 



an^rrd to Corrrsponlirntd. 



OJS^ o, „ VfiH- 



tlu Salmrdiif /■n.fJin} IXm 

 m ^ttkic^ •romi'fU vt to go to 



rl) allnlien lioulj rearh Ut 

 r <!/' KSOWLXDGB, 1*1 



• tkt ICMit. 



i.— 1. So ifut*tioiu Mkim^ /or tcifmt{fie i»/ormatioH 

 f<M. i Ltltm trmt to tkt Editor /or corrnpanilexU 

 tk* NiiM'a or aJJr^Mtt </ corrrtpomdentM bt aietn in 

 a. Corrrrpomtntt tkoitU <rrit« om one tidt o»7r 

 ,fp,ir,ile In/, k. Eaek leUer ikould 

 ICC tkouUl 6« mad* to itt number, tke 



n//V 



SI. B. Alhui. (1) Ah! if surmise wero but certainty. (2) In 

 lialf (111- 20,'JUO years the earth's axis has swayed through its pre- 

 i-cssiouul raii);e witli resijcct to the star-sphere; but its incliuation 

 to the plane of the ecliptic is not much altered, and, such change 

 as there is, is perioilic. (3) I do not know whether the gentleman 

 whose letter to your father you forward mo is now alive. — J. A. D. 

 If in an urn there are as many alphabets as there are letters in the 

 sentence, '• Up guard.<) and nt them " (i.e., 17 alphabets, or 4-12 

 letters) ; the chance thai these words will be drawn in their exact 

 order will obviously bo 



jy'7/2. 1'. 1 .1 .3.1 .2.1 .2.1.1.1 .2. 1 .1 .1 .' 1 



^412 . 441 . 440 



■i•i^ 



l.lx 



1 would not deprive you of the pleasure of -working out this little 

 sum fi.r yourself. — Qi:kksii.veb. ' If the sides of a rifjht-angled 

 triani.'l%|ux> in geonutrical progression, and the area 575), you get, 

 if you jiut the sides e<inal to x. .r\i, and xy', the equations — 



. ■- "■• j' + j-'i/'=i'!/' or 1 + >/'=!/' 



and x'!/-=579 

 whence v and x readily obtained. — J. IlAMir.To.v. That comet was 

 seen in Kngloud. Sei- subject Comets in my article on Astronomy 

 in the " Encyclopa-dia Britannica." It is a very celebrated comet. 

 — W. CorPEV. The work, if sent to us, shall receive what you ask 

 for — fullest consideration. — Jardi.ne Pehki.ns. .Saying the moon 

 lias an ai)pa^nt diameter of about a foot would imply that the 

 moon apjAared to be about thirty-six yards away. If this, regarded 

 as a roiemilic statement, is not nonsen.se, I do not know what is. 

 Have ^ou never seen the moon, as die rises above a di.stant hill, 

 appear larger tlftin a house on that hill, though you knew tliolinuso 

 Vj be a*f.'iio<I ileal more than a foiit both in height nnd breadth .' 

 .%)>rla*lit cliameters and distances between objects are nut measur- 

 able in-fect or yards, but by the angles they subtend. On the other 

 pOintKoutarQ riglit. Yes, my reference to indicating distance in 

 hogshoafis and kilderkins irn*, as you presume, a joke j yet 

 the absnniity is no greater than in indicatiug the appa- 

 rent diameter of the sun in inches. — C. E. lIuxKoi-. 

 Thanks for your interesting letter. — ^ Vf. B. May 12 is Old 

 May;da.v /in the gbnge in 'which I wrot!e— that is^ Slay' 12 coiTc- 

 sponda toljie day of year which before the style was altered was' 

 called^ Slavj 1. But if the ttylo had"'not been changed in the 

 eightecnth^ccntuiS' the year 1 SCO would have been a icap-yoar, 

 and fi.iy-daywriUrd'liave fallen on \Vhat I's now called SIay'13. lu 

 that .sense Sfoy^fs is f)ld .May-day. 'After the year lEOi) Slay 14 

 will l>e (Jld Slay-da'y. — K. Buowx. No 'such sketch-maps are sold 

 to my knowledge. Iii my " Ualf-Hours with the Telescope " data 

 arc 'nftfttioneil "for- their construction.— E. R. Cowi.EV. Most of 

 those points will be treated of in the series of papers on " How to get 

 Strorfglj"* Author cannot answer individual (|ucrist8. — ClauijIUs. 

 Xo niffdical ' nuin would give an opinion without seeing you. 

 SeverSI'non-medical men would, I daresay, tell yon " all about it," 

 if your. Ii^tter apix;ared. Seriously, you should not ask for opinions 

 which could nftfbftfbe utterly untrustworthy. — W. P. wishes to 

 know whore Turkish tobacco, incntioncd by " Constant Header," 

 page 7'.>, vol. ii., can be obtained. Ho mentions also that 

 alKiut one mile from Swindon Junction, in an extenhion lino to 

 Marlborough, the ballast of the lino is full of costs of fossil 

 shells a rich field for the geologist.—,!. U. T. wishes to 

 learn wh.it formula is used for lr>garithms with the aid 

 of the table in Dc Slorgan's edition of " .Shriin's Logarithms." — 

 «. Bkt.Nro.s. (1) Your solution of the top problem is quite inwl- 

 mixsible. How can it be said that gravity has not time to act ? 

 When a bullet is travelling at its swiftest, gravity finds time to act 

 with full effect. The difference )x;tween the pressure of the air on 

 the under and upfjcr surface of the top, again, whethor suflicicnt or 

 not to priHlncc any effect, acts upwards precisely aa the top's weight 

 acts downwards, though with much less cncrgj-. Therefore, if 

 gravity has not time to cause the top to fall by acting on the top's 

 weight, neither can it have time to cause the toji to rise, by pro- 

 ducing an upward air-pressure. {'!) With regard to the jiyramid, 

 the (juestiun rea.lly is how you conlil set up your p<.Tfeetly vertical 

 line M ft. high, and how from your horizontal line 100 ft. south of 



it yon would bring this Df>right into line with Alpha Druconis, 



Ac. What you say you would do, an astronomer or a praotioal sur- . 

 voyor would show you to bo absolutely impossible, with anything . 

 like the necessary degree of accuracy. On the contrary, the orien- 

 tation by slant subterranean ])assnges could bo made to all intents 

 and pur|H>se8 perfect. The passages would, at tirst, be bored with 

 only rough aj)pi-oximntion to the desired dii-ertion ; but the deeper 

 they were carried the more perfect would lie their working and 

 slant, because Alpha Uracouis could be oliservi'd along them at 

 every sub-polar passage. Whensoever tliey liiid been carried down 

 deep enough, a vortical boring could be carried down to the sub- 

 terranean chamber into which the slant passage opens, a plumb- 

 line could be lot fall down this vertical boring : it might bo a yard, 

 or a foot, or more or less (according to the success of this first rough 

 attempt to get a vertical mid line due south of the ontrancoj from 

 the observed direction of the visual lino along tho middle of thi? 

 descending jiassago to Alpha Draconis. \Vhatover correction 

 had thus to bo made, would, of course, bo made east or west 

 from the top of tho vortical boring, giving a point duo eontli 

 of tho centre of the entranco-holo of descending possoge. Th« 

 orientation thus obtained — practically perfect before the firsl. ■ 

 layer of stones was placed — would bo checked and improved 

 (to something like theoretical perfection) as layer after layer was 

 added. I'crniit me to say that no astronomer would regard your 

 plan lis capable of any scientific accuracy, while every astronomei- 

 secs the plan of a long slant passage directed to the polo star to be 

 tho only perfect way, though involving much labour and expense. 

 As a trifling detail, it may bo added that the passage is there with ' 

 the proper northing and slope. You may jirefer to believe that 

 though the passage is thus carefully directed due north, and with 

 an inclination bringing it to bear on the polo star of tho day, it was 

 really only meant for the sliding down of great stones ; so also 

 if you wero shown how jierfcctly the stand of an equatorial 

 telescope is suited to keep the telescope directed upon a star, you 

 might answer that, in your opinion, the instniment was intendetl ' 

 for a pump: but you must not expect every one to agree with you.— 

 LoKEsMiTii. — How do you make £0,960 in third year provide for 

 fourteen allotments of"l'500 each, with'£I40 8vArCi'— G. E. A. I do 

 not find anything in Mr. Clodd's account of deposit of stalagmitji- 

 over inscription to show that the deposit only takes place round tho ^ 

 letters and not over them ns well.— J. M. N. (j ray's Anatomy, 

 jirofusely illustrated. — J. Evans. With thanks. E. Cakus Wli.soN. 

 The subject has been fully '^discussed in e:irly numbers of Know- 

 ledge. The ice yachts only travel faster than tho wind when the 

 wind is more or less abeam. It can bo shown that when a yocht i« ' 

 running with a velocity bq'uhl to'the wind's (alu am) there remains 

 effottive driving action. , Do nut know whether tigers purr 

 like cats. — II. D. 'No, the funvard 'niofinii iloes not in any 

 affect the action of gi-avity.~ It is a law of motiiin that each forci- 

 acting on i^^body pipc^u^^ps its.J'ull egegj.— Tom T. {, Thanks. 

 Excuse delay ; your letter arrived %ylicn I was far from well. There 

 are delifflto ■liiil'characteris'tic 'distinctions' botwefen the business 

 type of face and Hhe literary or scientific type. They havo not, so ' 

 far as I know, 'been classified, as Lc Brun classificfd the effects of ' 

 different einotibns on ■the features (to refer only to'nrtistfo'classi- ' 

 fication)..; They are in no way connected with " tho science of' 

 phrenology ". (there 'is no such »cie»icc).— W. B. WicKen. ' Thanks i 

 for your veiy kind and ■ encouraging communication. — W. U. G. I ■ 

 fear it would' bb diflieult to obtoin any remunerative situation of the • 

 kind described. — E. X. Is it easier to swinf in deo]> thrfn in shallow ' 

 waters' It would be well- to be shro of th'o fact before Seeking to _' 

 explain it. I havo swum for more than unMrrfur- at a- time in doofi * 

 water, and for long spells in shallow water, without noting ony 

 difference of the kind. — EuiN-iiO.BnA(iiT. There are sevenvl methods 

 of vulcanising. One is to iminerso thin sheets of rubber in raeltcil 

 sulphur, and then roll them together. This is the most crude and 

 the earliest. I'arkes's is better. Tho rubber is immersed in 4(1 

 parts of bisulphide of carbon and 1 part of chloride of sulphur, 

 then heated gently and carefully till tho bisulphide is volatilised. 

 The rubber is next boiled in a weak solution of caustic potash 

 (■'JOO grammes to 10 litres), and then wosheil to remove the alkali. 

 I might add many other recipes, by tho aid of which, as with the 

 above, Eui.n'-oo-Bkagii ■will equally fail to obtain a moderately good 

 specimen until he has spoiled a hundred or less of trial samples. 

 and thereby learned the business. 



ELECTRICAIi. 

 A. II. H. The Maynqoth battery has aljout three-fourths the 

 electro-motive force of a Bunsen, but it is very uncertain, irrogular, 

 expensive, nnd altogether aii unpractical typie. Your other query 

 involves several nice points, but if Jlr. Editor can, find room, I will 

 deal with it next week. — S. K. Kei.p. Your castings, 1 am informed, 

 were duly despatched on tho 2Sth ult. If not yet to hand, write 

 again to the founders.- Steady Slilscuidi:!:. See answer li« 

 "Co.v8TA.NT Reader" a fortnight since. 



