344 



. KNOWLEDGE 



[Fita 17, 1882. 



riiio, until, by piilliii;; iti Imt tiin'nil, Blin ivducoi lipr flnntlng power, 

 and ao coiiicn don'ii :-' S|iM|i'r wvb, in iind of itself, is not lighter 

 than air J how, thon, i.i iu Imoyimcy to bn i-xplninoil ? 



In two «iiy«, I think. Whon tho Kiin i» HhininK, ovcry projecting 

 object, likt> n twig or stick, ubnorbK lu'iit more rapidly than tho nir, 

 bocomoH warmer than thi' nir, nml thiin rirts lik'- nii indi'|M)ndi>nt 

 ■ourco of hcnt in gciioraling nn nrn'mding rurront, no thiit whi-n 

 tho spider lets go her hold, she and her thrond are carried up partly 

 by tho action of this cnrrent. 



But thii* in not all : nnlcsn I am mnch mistaken, tht aeiion of the 

 «un'« ra<iit nn tlin thrrad itnrlf and its mirroundini) envnlope of air is 

 the main cause of its buoyancy. .\ir is nearly diathormanons, or 

 transparent to hant, so that the solar ray», in tmrorsing it. wiimi 

 it only slightly. The spiilcr's thread is not so, but in tho niiiiBliinc 

 worms up almost instantly, heating tho air in immediate contact 

 with it : and then, although the spider thread alone is heavier than 

 air, yet the thread and the adhering envelope of warme<l and 

 expanded air taken together, are lighter tlian the same bulk of tho 

 cooler air around, and thns constitute a qunsi-balloon, on which tho 

 spider sails away. (Jf course, if this is so, the poor creatures 

 cannot sail much on cloudy <inys, and F think, in f.ict, they do not. 



1 have tried n few ctporiiTients to verify the idea, and so far as 

 they go they all confirm it. For iDStancc, one day in the autumn of 

 1880, when the air was full of floating gossamer, and there was no 

 wind blowinsr, 1 caught some of the filaments at the end of a little 

 stick, to see how they would behave. So long as I stood in tho 

 sunshine, they streamed straight upward, tugging with almost a 

 breaking strain ; as soon as I stepped into the shadow of a building, 

 they lost their spirit, and drooped abjectly ; the moment I put them 

 in the light again, they resumed their buoyancy. It is, of course, 

 possible that in the shade there were local downward air currents to 

 account for their behaviour ; but once a cloud passed across tho sun, 

 and they drooped then, just a.i they did behind the building. 



The same theory will explain the buoyancy of any minute par- 

 ticles of dust or eraokc. So long aa the sun shines, they will absorb 

 its rays, become warmer than tho air, and surround themselves with 

 a buoyant envelope, which will carry them up if they are not too 

 heavy in pi-oportion to their surface. But if tho air is still, and the 

 sun obscured, they will settle down near the earth, in the way we 

 are all familiar with in muggy weather. Of course, if there is much 

 wind, this will mainly control their movements, and neither their 

 buoyancy in sunshine, nor their gravity in shadow, will be particu- 

 larly noticeable. — Boston Journal of Chemistry. 



INTELLIGENCE OF DOGS. 



WHILE at the University, taking my medical course, the facts 

 I relate took place. Among other appurtenances to the 

 department of physiological chemistry was a dog with a gastric 

 fistula, which tistula was properly healed around a silver tube 

 having an internal and external flange to keep it in place. The 

 tube was stopped by a clo.sel}--fitted cork, except .it such times as 

 we needed -.i supply of gastric juice. The fistula caused the animal 

 no disturbance whatever, lie was well and hearty, was fed at and 

 mu<le his home at the medical department. 



During tho summer vacation, however, when the University was 

 closed, he was transferred to the care of the surgeon, who took him 

 to his house. During his frolics one day he jumped over a fence, 

 striking it, and dislodged the cork in the tube. Ponto soon noticed 

 that his food didn't seem to satisfy him, and that all he drank ran 

 out of his stomach on the ground, ilis master having gone away 

 for several d.iys— fishing — he must needs take care of himself, so 

 immediately on eating or drinking anything, he ran to his bed in 

 tho carriage house close by, turned on his back, and remained so 

 for an hour or more, or until he felt satisfied that it would do for 

 him to get up. Coaxing, threatening, and kicking by the domestics 

 about the house, or by those whose attention was called to his 

 actions, were alike unavailing to drive him from his jilace or from 

 his supine position. Finally, some one who knew for what purposes 

 the dog was used, examined his fistula and found the cork gone. 

 This being restored, he was soon porsnaded to go about as usual, 

 and indicated by his actions that he understood that everything 

 was all right. This incident can be vouched for by many reliable 

 persons. Who will say that dogs — at least one dog — cannot reason ? 

 — F. L. B.\BDEEX, M.D., in Scientific American. 



Point's ExniACT ia a certain care for Rheamatism and Gout, 

 Pond's Extract is a certam cure for Hrrmorrhoids. 

 Pond's Extract is a certain euro for NeunUKic paina. 

 Pond's Extract will heal Burns and Wounds. 

 Pond's Extract will cure "nrains and Bruises. 



Sold by all Chemists, Qet the genuine. 



arttrrs to tl)c eiiitor. 



\Th« E'Jitor do*» n<>t kuU him»e{/'rtrp9ntit!r/,jr tk« opinionm of hi* eorrtKpondniM, 

 B« Ciinnot tindrrt'ikf to rttu^n monutcrtptd vr to rorreMpond rUk tkeir tpritm, AU 

 communu^atiotu gkotlJ be a* akorl om posnble, contisttntlf rt/A /uil and clear tlat0' 

 menU of Ike tcritrr't m*anirttj.'\ 



AH JCdiforuii romMumi^<jiionM akouU h» nddrtutd to the Editor of KhowlVDOI; 

 aU BuMUteu eommumcattona to the rulliskert, ai tA« OJict, 7«, Qrtai Queem- 

 ttreet, W.C. 



AU Rtmittanrfn, Ck^quea^ and Pott-OJlce Ordert tkould be made payalle to 

 VetTt, Ff'tfRKin 4* Son*. 



*.• All Uttera to tke Editor will he Xumber^d. For ecntmienc* of r^ertitet, 

 fOTTfiiponJenie, trh^n r^erring to any Uttgr^ wiU oblige by wuniioninff iU numJm 

 and tk^ pf^g* on vrkich it appeare. 



All Letter* or Qu^riet to tke Editor rliVA re*jtiire attention in the eurreni ieeue ^ 

 Enowledob, thoutd reaah the Publieking Office not Utitrthan th« Saturday preceding 

 tke day qf publication. _ 



■e; thoT moft be dnwB 

 I hat I her maj gu unt<jurhe(l to Uw ' 

 printers ; private cnnimuiiiraii« ns, ther.^fure, it« well aa queries, or replin to 

 queries (intended tonpppar ax flucfa) should be wrilien on Bepnrale lesTea. 



(II.) Queries and roplieA shoi>ld be c\Qn more ct-ncUe llutn letlors ; and drsvB 

 up in tbo form in which Iher are here prc>fni*'<l, with brackets for number in cam 

 of queries, and the proper query number (bra<;ke(tHl) incaf^e of replies. 



(III.} Letters, queries, and repbes nbieh (either becaoso too lone;, or ansnitabla^ 

 or deahnj; vritb matters which otnors hare dincuDsed, or foranj other reason) caA> 

 not find place here, will either be briefly rt-ferred toinaaswerstocorretipoDdeDta, or 

 acknowledged in u column reserv'ed for thepurpofle. 



(I.) Letters to have a chance of apnciirin^ mn^t 

 p in the form adopted for lellen* liere, bo that 



s to be contemned and deiapised who is not in • 

 there anything more adversA to accoraoj 



" In knowledfje, that man ( 



st&to of transition iSo 



lUan fixity of opinion,** — Faraday. 



" There is no narm in making a mistAke, but ^Oftt barm in making none. Bhow 

 me a man who makes no mistakes, and I will show you s man who b«s don* 

 nothing." — lAebic. 



" GoJ'h Orthodoxy Is Truth."— C»«W« King'^Uy. 



©MX Corrrspontifnrt Columns. 



OPTICAL ILLUSION.— CAT'S EYE TIMEPIECE. 



[279] — In the long string of optical illasions which have appeared 

 from week to week in yoar esteemed paper, I am surprised the 

 followin^T bas not been mentioned : — Fix an ordinary fork in the 

 wall, and on the handle balance a small cork. Having shut the 

 rijrht eye, walk towards the cork and endearour to knock it off with 

 the little finger. It is very seldom that the cork is displaced upon 

 first trial. 



Your account of the remarkable ingenuity of the Chinese in cal- 

 culation reminds me of the peculiar manner in which they are able 

 to approximately tell the time, no matter whether tho day is clondy 

 or dull. They will run to the nearest cat, open her eyes, if they 

 are not already open, and will at once inform you, with a certAin 

 amount of accuracy, what time it may be ; all depending, of conrset 

 upon the contraction of the iris or the size of the aperture of the pupil 

 of the eye. Wha.t 1 cannot understand in connection with thiti process 

 is, why the clouds in interrupting the sun's light have no effect upon 

 the cat's eye ? But I suppose the Celestial land knows not what 

 fogs and mists are, and therefore we should not be able to avail 

 ourselves of the advantage of feline clocks here. Even if it were 

 so. I question whether pussy would submit with such grace as the 

 rats in the land of the pigtail seem to, to an operation which mast 

 of nocossity be far from agreeable to her. — Yours, A'c, 



EBNEST J. WERVHAlf. 



fADTT 



WEATHER FORECAST. 

 [280] — I noticed in one of the numl>ers of your most valuable 

 publication, viz., Knowledge, some remarks anent the conntant 

 inaccuracies in tho weather forecasts of our Meteorological OflBoe, 

 and impugning the utility of them and the cost to the nation, out of 

 all proportion to tho benefit derived. As regards our o>vn district, 

 viz., North Wales, we are coupled with Lancashire and N.W. 

 England, some ninety miles off. notably one of the wettest districts 

 in England, and not one in twenty of the forocafits is correct as 

 applied to us. I tested them for fourteen days, and not one was 

 correct, which I forwarded, in a tabulated form, to the office, giving 

 on one side their own forecasts and on the other the actual weather 

 we had experienced, and stated my o{)ini<»n of the uselessness of 

 such forecasts and the injustice of tacking as on to a district so 

 far away; in due course I received a reply from the secretary. 

 which 1 am sorry I destroyed, otherwise you should have aeon 



