3<.Ki 



• KNOVv^LEDGE 



[Mabcii 3, 1882, 



[271] — The KLiu-rKofiioTE. — Somo two yonrn ago, an invcntiun 

 cnlli'd tlin flectriiphn(<< wiiH niiiiniinroil, tlio nniiio imliuitijiK. of 

 courKo, ttinl rnvM »f lif-lit. roiild lio tniimniittoil nlnii)^ tlic clcotric 

 wip', n-prixlucinu at cmo cml of it tliu iiiiiiKO of olijcrtB visible at 

 the otlicT. roiild you, nr »omi> rontribiitur, (five your rondorK hoiiu- 

 infomintioii r<<K>inliiiK thin wonderful but obncuro invention, or Hliitr 

 when' Hurli t-ould be found ? -HoUKAS. | Tliero mny bftvu l>ecn mime 

 inatrumenl by which ii liBht-roronl of Home Rort wuaconiiuunicatod; 

 but nolliin^ anob nH "IJorcns" doacrilH>H I'ould hnvo been nceoni- 

 pliahoii ill thiH wnr. Tlio aclonium vicctrophoto Ntory ia probnbly 

 rpforrod to. — Ko.J 



[272] — The Mkami'Iieh of Time and TKMPKRATrRE. — Will yon 

 kindly inform mo how wo know that two port ions oftimo arc 0(|ual, 

 and how wo know that the difTerence of temperature of. for instance, 

 (iO°t' and 70°C ia the same ns the ilifTeronco of 70''C and KO'C ': — 

 Fkank Miller. [Wo may nicasnro time by any movements wo 

 have reason to consider uniform. Aa to heat mcnaurca, our detcreca 

 are arbitrarj-, and we know, us a matter of fact, that the expansion 

 of mercury is not absolutely uniform for uniform increase of tem- 

 perature, ihon^h very nearly so between certain limits. — Ed.] 



[273] — Strenoth ok Materials. — On page 217 of Anderson's 

 "Strennib of Materials" (IjOnpman'a " Text Books of Science") 

 the equilibrium of a 30*ton crane ia under consideration, and it 

 appears that tlie Ijalanco of tho vertical downward pressure upon 

 the guide-rail (108 tons) and tho vertical upward pressure upon the 

 centre pillar (72) exceeds tho total load upon the structure (30 

 tons). Is this according to mechanical principles V and if not, 

 where is tho fallacy in the reasoning which leads up to it ? — 

 Libra. 



[274] — Miscellaneous. — Will any reader briefly inform me (1) 

 how to sort out the foraminifera of chalk for the microscope ? (2) 

 where to find a >-<?s«int' of hypotheses on the ventricles of the 

 brain ? (3) how to get, quickly and cheaply, some notions of draw- 

 ing ? — EozooN. 



[275] — Salt. — On what grounds do many people object to tho 

 use of salt with food ? Is this objection shared by any of our liigh 

 medical authorities? — Speculum. 



[27G] — PnoTOGRAi-nic. — Would " A. Brothers " or any one else 

 kindly give me their opinion on the following? 1. How to prepare 

 iodized collodion, giving the proportions. If this would be too 

 troublesome, as I have heard it is, where and at what price could I 

 buy it ? 2. Where can I buy tho metal plates so much used by 

 travelling photographers, how are they prepared in tho conditions 

 they are sold, what further is necessary for taking portraits by 

 them, and what price are they ? 3. How are tlio.se papers })repared 

 sold with an imitation camera, and a small quantity of some white 

 crystals to be dissolved in warm water, when the papers are dipped 

 in the solution, hideous faces, lic, are developed ; and what are tho 

 crystals ?— W. E. F. 



[277]— Luminous Paint.— Of what is it comimsed?— W. E. F. 



[278] — Smell from Burning Gas. — What is the precise cause 

 of smell noticed in room where gas has been burning for a time ? 

 It is noticed chiefly where a globe is used on the bracket. Is it 

 bad consumption, to be remedied by better burner or more air, or 

 is it caused by bm-ning of particles of dust accumulating on the 

 globe ? — Alpha. 



[279] — Stamina. — Would Mr. Grant Allen kindly explain the 

 origin and nse of tho circle of pale green cups which sun-ound the 

 stamens of the Christmas rose ? — Tyko. 



[280]— Actinium. — Can any reader tell me where I can get zinc 

 white pigment whicli turns black when exposed to sunlight, as I 

 liave not seen any sample of zinc white turn black, when exposed 

 to light as mentioned by Dr. T. L. Phipson, F.C.S., in Chemical 

 News, some months ago ? — Ekin. 



[281] — Reflecting Telescope.— Which would bo best, a metal 

 or a glass mirror, and what metal would bo best, as I am thinking 

 of making a reflecting telescope ? — T. Jones. 



[282] — Is the use of smelling salts beneficial or otherwise? 

 Why is it they are freely used by women, but not by men ? — P. M. 



[283] — Gla.ss. — At what temperatures do crown and./?iii( glasses 

 snch aa are used for telescopes come to the state of fusion neces- 

 sary for purification from striae and bubbles ? What materials are 

 best suited for crucibles and moulds, resisting tho high temperature 

 of the molten glass and unattacked thereby ? — Q. L. 



[28-1] — Pencil-Point Protectors. — Will any reader kindly inform 

 mo how to restore the silver ap))earanco to small articles made of 

 the same material as pencil-point protectors ? — Economist. 



[28.5] — SciENTinr Terms. — Wanted, the name and the publisher's 

 name of the host dictionary of scientific terms ? — Prestek W. 



[28G] — Electricity.— Wliich is the simplest and best text-book 

 poblishcd on electricity and magnetism? What is tho best kind of 

 galvanic battery for strengthening the nerves ; and what would bo 

 the price of same ? I do not want an expensive one. — W. H. 



[249]— AiwTBAtT Reasomnc. — In tliirty years' reading on logic 

 and philoKiphy, I never met with a diatinction Iwtwecn " objec- 

 tive" and "aubjective" r(>aaoning ; I am inclined, therefore, to 

 doubt if auch a distinction ia generally recogniaed. Again, Mr. W. 

 L. Abbot aaka for a " definition of nbatract reaaoning." I auppoM 

 Riich a term might mean either («) reasoning about abatract nib- 

 jocta. auch aa mathematical problcma ; and (6) reasoning uboot aiy 

 anbjecta, abstract or otherwixe, according to the laws of pure iogit, 

 aa diatinguiahcd from analog}', and perhaps, too, "inductive" 

 logic. — E. IJ. G. 



[259] — Ventriloquism. — My qualification in offering explani^ 

 tions in this regard conaiata in tho fact lliat I have long boon « 

 student of, and am the author of papers on, the subject of apoocl^ 

 production. The word ventriloijuism means, strictly, '" beU]^ 

 speaking," a phrase which is really most inapt. Ventrilixjuism. UL 

 essentially, semi-speech. The tongue, which is the chief agent of 

 speech, may be said to possess, practically, an interior or vertio^) 

 root, and one of a posterior or horizontal character. Wlien th^ 

 tongue is drawn back abnormally upon these baizes, the lower jaw 

 and lip will be found to protrude, and to assume a tixity of con- 

 dition by reason of the correlation of the muscular powers centred 

 near the laiynx. In producing speech under the above conditions 

 the main secret of the ventriloquist's art ia readily discovered. 

 Imitation of natural sonnds is effected in modulating the voice, 

 either by contraction of the larynx or by disposition of the nasal 

 cavities. The only real difficulty lies in mastering or modifying the 

 lip consonants. As in all other matters, perfection is only to be 

 gained by continual practice. — H. W. — [Answered by several 

 others. — Ed.] 



[260] — Lightning. — " Secretary " appears to have had a very 

 good illustration of the effect of a "return stroke." When a charged 

 body is brought near a neutral one, it has the power of polarising it. 

 Thus, the ground immediately under a heavily-charged thtindeig- 

 cloud becomes highly polarised. When the lightning passes, tl^ 

 neutral condition is suddenly restored, sometimes doing mow 

 mischief than the lightning. Suppose the cloud, A, to be chargH 



+ \y, then, of course, the surface of the earth under it i^ 

 become — the -H electricity being repelled as far as possible frWi 

 the inducing body (the cloud). Wlien the charge in A is too gittt, 

 the insulating air is pierced, and the flash passes, say to B. Tbit 

 cottages, C, being above the general surface, are more — ly charged 

 than the ground, and feel the " return stroke." Tjmdall's "' LessoM 

 in Electricity" will help " Secretary." — Euclid. 



[268] — Photography. — Will "Anon" say what purpose he 

 in view, whether portrait or landscape photography, or the 

 cation of photography to some special pnrjiose, when, as an ama 

 of experience, I shall be most happy to advise him. Eti pnfsaiU,A 

 is as well to remark that the practice of photography has 

 completely revolutionised during the last two or three years, and m 

 is almost impossible to name any work on the subject suitab' 

 for a beginner, since the information he would need still ren 

 squandered through the various technical publications of the' 

 few years, not having been as vet condensed into handbook form^ 

 E. T. W. 



[347] — Wild Flowers. — The nearest approach to E. Tayk 

 requirements is Rev. C.Johns' " Flowers of the Field," 5s. (S.P.C.Ki)i| 

 containing a number of illustrations, as well as descriptii 



EUPTERIS. 



Brewing. — To add to list of books on brewing : — " Bren 

 Practical and Scientific." by E. R. Sonthby. M.R.C.S., F.C.S., pn 

 lishcd by us {Country Breiirr.'i' Gazette) ; •■ Brew^ing," by J. Her 

 Burton-on-Trent ; and "The An of Brewing" (Cornish, Uolbora);j 

 — C. Dewston. 



