410 



KNOWLEDGE 



[March 10, 1862. 



(J?llfrif5. 



[2S7] — Fbhrikii'ii Infi.I'knza Vowder. — Cnn niiyoiio give mv Dr. 

 Forrioi^i prcnoriplimi for iiiOuriizn, mndu up of biHiiiulli, nrncia 

 |iow(I<-r, anil niorpliiii, to bv takvii in tlio form of anulT ? — ArrLUTKU 

 KnisciiiiiEU. 



[a^iKj — ri.A.VTK IN Hkc'Roous. — Are growinj^ plants unhcnltliv in 

 the bi-<Irooni ? If »'>, xlmuUI bi- i^hid to know tlio reason. — J. C. I.. 



[2H'.t] — TiiK BiKiAi. OF Mosfx — Wlicro cnn 1 obtain the piHin 

 cntitlod "The Huriiil of Moses," or where does it ocenr? — .1. C. L. 



['i'.'O] — Tkiitiaky ?'os8I|,«. —Can any of your renders exphiin liow 

 it iK pyritous fussils from tertiary beds are so apt to fall to pieces, 

 while those from secondary strata remain unaffi'cted by oxpONure to 

 the air? I have ctamples of ammonites, Ae., iu my cabinet that 

 have been there for years, and, althouRli quit« " brassy " in ajipear- 

 nnee from pyrites, yet remain entirely unchnn(;ed. — W. D. C. 



[2!ll] — IlAZOK. — Why does a ra/.or cut better after it has been 

 dipped in hot water ? This query answered on philosophical prin- 

 ciples will oblige.- H. Jo.-iK.i'ii Hoim.tox. 



[:i02] — Sil\t:r. — How can I molt the residue of old silver baths 

 80 as to obtain pure silver ? Can it be done in any way without 

 using a crucible ? IIow much can I obtain a crucible for ? — 

 F. A. B. 



[203] — Shelling Salts. — Is tho use of smelling salts beneficial 

 or otherwiiie ? Why are they resorted to profusely by women, but 

 not by men P — F. M. 



[294]. — Exceptional Season.s. — IIow is tho exceptionally severe 

 winter of 1880-81, and the contnist in the exceptionally mild winter 

 of 1881-82, to be acconnted for ? — F. M. 



[2il5] — AiTAKE.VT Parapo.k IN I'lioiiABiLiTiE.s. — A bag contains 

 an indefinitely great number of marked tickets, the nature of the 

 marks being unknown. One liundrod tickets are drawn. These all 

 bear letters of the alphabet, viz., 50 bear A, 30 B, and 20 C. Then 

 (r. I.ubbock and Urinkwater Bethuno's "Probability," p. 27), 

 the chance that the next ticket drawn wnll bear a letter of the 



101 



103 



lul' 



That is to say, tlie chance of the next mark being one of 



the 3 letters A, B, C, >e greater than the chance of its being one of 

 the 20 letters A to Z. Where is the fallacy in the reasoning? — 

 Gkaiutim. — [In the former case wo have the probability that an 

 event will be either of one kind shown to be prevalent in a certain 

 degree, or will not be of that one kind. In the latter wc have the 

 probability that it will be one of three kinds shown to be i)re- 

 valent in certain degrees, or will not be of those three. The evidence 

 for three distinct kinds of marking gives stronger reason to believe 

 that the next will be one of those, than the evidence of one sort 

 of marking gives in favour of the next belonging to that one kind. 

 The paradox seems to arise from this, that in calculating the chance 

 of the next being a letter, we do not take into account the evidence 

 ten ling to show that there are three prevalent letters in the bag. 

 See aljo De Morgan on " Probabilities." — Eu.] 



[290] — PiioTOGRAriiic STi'nio. — I wish to construct a reasonably 

 inexi)ensive glass-house, and shall feel obliged by a few hints as to 

 (a) dimensions, (b) material for walls and roof, and (c) arrangement 

 of light, having regard to the fact tlicit the studio will have to join 

 the back of my house, which has a S.W. aspect. A reference to 

 any work on the subject will also oblige. — Am.\teur. 



[297] — LiMF.-LiGirr Appakatl's. — Where could I best obtain one 

 cheap, suitable for illustrating lectures to workmen with, and what 

 wonll be about the probable cost of the instrument complete? — 

 W. R, 1.. 



[29S] — Odb Axcestors. — We are told that the p.ateolithic man 

 who inhabited Britain was black in Mr. Grant Allen's interesting 

 article. How is this known to be so ? There is no evidence offered 

 in the article, and I should be glad to know how this can be proved. 



— HOMO PAL.i:OLITIIICfS. 



[299] — Magic Lantern. — Is it possible to make a magic lantern 

 in wood suitable for an ordinary room ? If so, could you kindly 

 give direction?, or mention some book (with price) on the subject ?— 

 Amateiu Carpenter. 



[300] — Does the learning by heart of prose or poetry iniin-ovc or 

 impair tho faculties ?— A. C. 



[301]— Magic Lantern. — I want to make a lantern for scientific 

 illustration. Can any reader tell me the size, focal length, and 

 distance apart of the glasses to bo nsed in making one to take 

 photographic slides ? — P. D. H. 



[302]— Vegetarianism.— Can you tell mo of a good book hercoK ? 

 I know not what vegetables to "eat, or how to cook them.— John 

 Alkx. OLLAKn. 



[3v>3] — Destruction of Souo.m and Gomorrah. — A clcrgvmnn 



preaching on thi( aabjcct stated that it had l»ecn olmoiit conclusively 

 proved, on scientific grounds, that these towns were deslroyed by a 

 iihower of mcteon* on July 31, 1^98 n.i'. Is there any proof of 

 (his ; and, if so, what is the yirixil ? A. X. 



[301] — (iEouHjv. — Can any geologirnl reader recommend a good 

 work on the carboniferous liinesionc formation, which contains re- 

 liable information as to fossils ; more especially as regards the 

 North Wales and iShropshire rocks ?— A. N. 



[305] — The Calcilis. — What books should be rend on the 

 c.ilculus after Todhunter and Willinmson ? Is Price's " Infinitesimal 

 Calculus" a good book ? — Mathematici's. 



[306] — Scholarships at Camiibidge. — Arc any open to candi- 

 dates over twenty yiars who have not already entered ? — Mathf- 



MATICt'S. 



[307] — Descriptive Geometry. — Bcqiiircd, a work on this subject, 

 Nufliciont for a first class in fourth stage mathematics, that is, 

 fulfilling the following syllabus : — Representation of points, straight 

 lines, and planes, by projections and traces on two orthogonal 

 planes. The use of auxiliary projections and rabatments. Graphic 

 soIuti(fns of problems concerning straight lines and planes, their 

 intersections, inclinations, 4c. Problems on trihedrsil angles. 

 Your paper supjilies a want in educational literature. — Self-Tal'oht. 



[308] — Quicksands. — Why do persons sink in quicksands deeper 

 than they would in water, and why can they not float as in water ? 

 Does the sand in a qnicksand float in the water, and how is that 

 compatible with the relative specific gravities of water and sand ? 

 If not, why does not the sand sink in the water? — John R. West. 



[309] — Effects of Tobacco. — Will Dr. Muir Howie kindly explain 

 why persons suffering from asthma are sometimes recommended to 

 smoke tobacco ? I gather from his interesting paper that the use 

 of the narcotic would tend to lessen the resen-e of vitality so 

 necessary to resist the effects of violent attacks of coughing. — 

 J. W. Brookes. 



[310] — Quartz in Coal. — I have in my possession a specimen of 

 coal to which a piece of quartz is closely attached, several layers 

 of the same rock also running through the coal. How can this be 

 explained!' — J. W. Bkookej. 



lAfpIir£i to (Surrifsf, 



[220] — Chemical Analysis. — Might I say that before buying the 

 new editions of Fresenins on Qualitative and Quantitative Analysis 

 — which, as one of your readers has rightly observed, are rather t«o 

 descriptive to be of use to a beginner — he should try and obtain 

 the previous edition, which the translator cut down to about half 

 its original volume, thereby making it as valuable to the novice as 

 it is to the chemist. Your correspondent must not be surprised if the 

 second-hand books should be as expensive as the new books. — 

 r. C. S. 



[258] — Drying Wild Flowers. — " H. R. S." should take to 

 Egypt and Palestine with him a quantity of botanical drying 

 pajier (to be had, of any scientific dealer), and two or more strong 

 wooden boards of same size as paper ; also strong leather straps. 

 Tlie plants should be spread out as naturally as possible between 

 the sheets of paper. Then lay all between the boards, and put one 

 or two large and heavy stones (to be had at most places) on the 

 top. Try to keep some of the paper not in use, so that it may be 

 changed for that in use, which becomes damp from the moisture in 

 the plants. This changing should be made every second day, if 

 possible. When travelling from place to place, strap the whole 

 firmly together. — F. W. G. 



[25S] — Drying Wild Flowers — page 861. — I should recommend 

 " H. R. S." to got a small 5s. book by J. L. English, entitled "A 

 Manual on the Preservation of the larger Fungi and Wild Flowers," 

 just published by A. B. Davis, of Epping. There is a small collec- 

 tion of wild flowers in the Norwich Museum preserved by this 

 process, in which both colour and form are beautifully retained. — 

 R. S. Standen. 



[20 1] — Letts's " Popular Atlas Geographical Map of England and 

 Wales" (with leading railways), will give "Strata" the informa- 

 tion he asks for. Also Professor John Phillip's "Geography of 

 Oxford and the Valley of the Thames" will be of great assistance. 

 A very bright and clear geographical map (of England and Walea) 

 is prefixed to Mr. 11. B. Woodward's "Geology of England and 

 Wales." Letts's map is a very cheap one, and is tho work of Mr. 

 Bristow ; it is founded on Murchison's map. Should be gl.ad to help 

 " Strata " in any way I can. — Jaciebat. 



[207] — Thoracic Integrity. — The statement in " Science for 

 All " is perfectly authentic. It is really not correct to regard the 

 chest cavity as being air-tight, as, of course, can at once bo under- 



