t38 



KNOWLEDGE 



[Makcu 17, 1882. 



not to niik why I think it np)iroprinto to Irinh kWI*. Moon'ii phnM>« 

 cnn Bcnri'i'ly l>" ox|iliiiiif>il 1iiti>, nil (hey nr<> cxphiiiicd in cvrry n- 

 N(H'ctnl)h< Irxt hiMik iin imlnmoniy. — II. D. Haiiii.aV. A mini Hiiglil 

 Itr wiid t<i 1)1' oviijvi'il from a Imliy, or »ii onk from nn iicorii ; but in 

 tho acii'ni'o of our tiiiio tlio tcnii evolution i< ({rnt'mjly npplit'cl to 

 tlip ilovplopmcnt of Hpci'icH. — A Sciiooi.iiov. Tlio reiiHon in thiit tlio 

 oarth Koi'i roiintl thi< hiiii oiico n yonr, no thnt tin* Htars on thu 8i(lo 

 opposite tho Hiin ncci'HHiirily ohnnKC Imiif^inc ii lon)<, KtmiK'ht linn 

 from tho «un to tlio oarth and beyond. 'I'hlH would point in one direc- 

 tion nt the bcRinnintf of n month, in n rliunifed dirertion (beeauae of 

 the earth's motion) at tlie end. — W. H. tiiioVE. I'nrdon mc, it is you 

 who are wrnn); in ilciiyintf lliat to (jivi" an equal chance of » piir- 

 ttoitlar event, such r8 all the tnimp.i being in one hand, there miiHt 

 be a certain number of trials. You are riffht in sayinR one parti- 

 cular arrangement is as likely as any other, but it is very far, 

 indeed, from an even chance tliat that particular nrranj^emont will 

 appear. You shall correct tho mathematical discussion of this 

 point, if you like and can, when it appears.— ARciiiMiM.io.N. Your 

 *' cosmetical specimens of angularised forms" too much for US: 

 we need rest after your letter. — W. W. There is nothing to make 

 the earth assume a more upri).;ht position. The removal or 

 burning of all the coals in the plobe could not affect her 

 axial poFO, even if they were all at one spot in the northern 

 liemisphcre. — S. S. H. By triangle of forces, the actual wind 

 FE (Fig. 2, p. 36), and tho wind EC, resulting from yacht's motion 

 in direction CE, would bo balanced by a wind CF, and, therefore, 

 their resultant is a wind FC. 2. Well, you might, for such a problem 

 as you require, take this. Assuming frictional resistance constant, 

 and sail (iO always set to bisect the angle FCE (as this angle varies 

 with the increasing velocity of tho yacht), determine the maximum 

 velocity which the yacht can attain on a given course and with a 

 given wind. Do not ask me to solve this, please, for time will not 

 permit. — A. H. Moselev. We partly think with you that the stories 

 on '"Intelligence in Animals" have now run far enough; but we 

 have to consider, what perhaps you overlook, that many readers 

 take much more interest in such matters than in those with which 

 you wish to see Knowledge filled. Your friend who told you that the 

 very amusing and well-written sketch you object to would have been 

 sent to the W.P.B., but for the military rank of the writer, is no doubt 

 one who understands very thoroughly his own nature, and judges 

 others accordingly. Those who know me best tell me I err in the 

 other direction. Need I say 1 do not agree with them ? but at any 

 rate, they know me ; your friend very manifestly does not. Y'ou say 

 •give us more astronomy, instead " of such articles; but for one 

 who so addresses me there are tens, or rather fifties, who say give 

 us more that is light and readable. Of cour.se, if all readers wanted 

 deep scientific matter, I should feci bound to considy them ; but I 

 expect that would mean such a limited array of readers that 

 Knowledge would very soon come to an end. This point 

 has to be considered, you know. Oddly enough, yon arc the 

 first who has written objecting to tho introduction of 

 these stories (except one who gave a semi-religious reason). 

 Nov the round is complete, and ereri/ subject dealt with 

 in Knowledge has had its tui-n. If all were listened to, 

 therefore, we should appear with blank pages. Y'et all who have 

 criticised special subjecis have done their beat to advance our 

 success. Man}- thanks for what you have done in that way. — Geo. 

 BoBSON. We are thinking of having "vellum wove," with illumi- 

 nated borders and headings. Your own special copy shall be printed 

 in gold letters on purple-tinted silk, delicately scented. Yet we 

 fear you would not even then be happy. Will it cheer you to be told 

 that the average cost of the numbers since January I, instead of 

 being less, as you fondly imagine, has been half as great again as 

 that of the fii'st nine numbers ? In this, of course, is included one 

 very important item, which persons who, like yourselves, complain 

 of paper, folding, and so forth, persistently overlook. — C. O. Thanks 

 for your very pleasant letter; it does me good after G. R.'s 

 sour one. Y'ou have not the problem at p. 3S0 quite right ; 

 you take a square plus a square, and the figure is a square 

 miniu a square. — Gn.\ts. Very likely you are right in assuming 

 that thin-skinned persons are preferred by biting insects to those 

 with less penetrable cuticles. — Lewis Akundel. Questions 

 already answered, or in course of being so. The mistake in 

 letter 280 is annoying ; it is one of those cases of perverted inge- 

 nuity which are a)>t to escape the "reader," for his attention is 

 directed to orthography, punctuation, syntax, &c., so that tho ab- 

 surdity of a statement, as such, is apt to escape his notice. — Percy 

 B. Donn. Thanks ; but the problem has been already dealt with 

 in Knowledge, No. 8, p. 16G.— Edward Stubb.s. I have carefully 

 compared the weather records for the years 1768 to 1792, left by 

 White of Selborne, and find not the slightest balance (even) of 

 evidence in favour of the theory that tho weather repeats itself 

 after seventy-six years, in England, at any rate. — F. Cowley. 

 Thanks. About photography, Mr. Brothers, of Manchester, has 



kindly promiiod to write for ua. Tho other queiitiona already 

 answered. — IIallyakdh. I did not mean that 1 could jaiit 

 Hfe the lumidre reniln'p in America a day liefore first 

 quarter, but that it was then strikingly obvious — as obvious a« in 



Knglaiid when moon shows but a narrow cresrent. When you saw 

 • ibjectH more clearly through moist air, they must, you think, have 

 been magnille<l ; but were they ? Surely you could tell whether 

 objects looked larger or not. It is absolutely impossible that 

 moisture in the air should magnify. I am cpiite with you about 

 differences of eyesight. I can see details with my naked eye 

 (literally eye, for it is only one which has tie power) which some 

 tind diilicult to see with an ordinary magnifying glass. Bnt 

 personal differences such as that have no liearing on the question 

 whether moist air magnifies. You speak of a change of tone in my 

 commnnicatiims to tho E. M. after 1S72 ; possibly you refer to 

 letters in which I exposed the jobbing schemers. Truly, then I did 

 vot mean " legitimate playfulness." I laid on tho lash with 

 intent, and with tolerable [effect. Looking back now at that time, 

 I see nothing to regret except occasional leniency. Sorry it jars on 

 you to hear our writers speak of "Huxley" and " Darwin" and 

 so forth. It would jar very much on me to speak of Mr. Darwin 

 or Mr. Uerbert Spencer. Will ask the publishers whether the 

 quadrifid ornaments on either side of the heading of each page 

 ought to hurt readers' eyes. Are you not rather sensitive ? The 

 large maps can be bound up as the double-])age pictures in the 

 Illustrated and Graphic are bound. As to the words which seem to 

 imply that the Egyptians were acquainted with the earth's motion, 

 surely there is some difference between them and references to the 

 rising, setting, and motion generally of the sun and moon. These 

 bodies seem to move — the earth does not. Does an open fireplace 

 help to ventilate a sick room ? I know something on that score 

 from experience, and I venture to say that if there is a place where 

 our open fires are greater nuisances than elsewhere, the sick room , 

 is the place.- -J.NO. SiTnERLANn. We cannot undertake the office' 

 of private tutors to individual readers. Nine-tenths of the initials, I 

 Ac, under head "Letters Received" belong to correspondents j 

 who ask such question as yours. If we had space, 

 should not have time. Again, if you must ask questions in- ' 

 volving the use of the differential calculus, why use the | 

 fluxional notation ? To use Babbage's old joke, we prefer d-ism to ] 

 dot-age. Lastly, to your question : (we answer just this once) yon j 

 could hardly expect to get the right differential equation if yoa] 

 treat T as a constant, even though it be only once. "You have] 

 (I'll /''"X I 



TJ7 = V, and you say .".I -j- l'=2vr-f C ; but 1 is not constant;! 



indeed yon write down eventually to an equation in which there isl 



a term involving 3—. " That's how the error has arisen." — B. C. 



° ax 



Fraser. We must wait till the microscope has shown the diamonds] 

 in the razor's edge before we take that for a reason. — A. Blake. J 

 Other suns and systems might, of course, have originated as our sun ' 

 and his system have done. We are not nearly so clear how this has ' 

 been as you seem to imagine. The " sweet influences " of the Pleiades ' 

 have been explained in several ways; there can be very little doubt the 

 reference is to the supposed influences of the Pleiades when the sun , 

 was in their neighbourhood ; just as Sirius was supposed to combine 

 his rays with the solar rays, later on in the year, to produce unpleasant ■ 

 effects, so in early spring (when in Job's time the sun was passing ' 

 the Pleiades) the germinal influences of the season were attributed j 

 to those stars. — J. M. Fothergill. Of course. Cotton Mather was' 

 an American ; I thought everyone knew that. Tlie story is told by ' 

 Wendell Holmes, in his Breakfast series. I referred only to the 

 " irreverent." It struck me as good fun to hear that strict, solemn, '"j 

 and most rigid Calvinist charged with irreverence — enough to make ' 

 him turn in his gi-ave ; albeit one may note a good deal that is 1 

 very irreverent indeed, in my opinion, in his " Remarkable Provi-'! 

 dences." 



ilrttrrs iArrribfti. 



A. Hargreave. J. J. Snellgrove, M. M., Neminis Umbra (« 

 cannot see it). Willow, M. Paterson, J. K. L., M. Petersen. Bine 

 Peter. An Admirer, Constant and Thorough Reader, Lucasian, P. 

 Parley, Titmouse, Aggrieved One, Patience (just what Aggrieved 

 One wants), L. Prowse, Ternary, S. Smithson. B. J. Harvey, 

 Amused, Vegetarian, Prospero, M. Macnnlty, Jerry, P. T. Heffeman, 

 Harpax, Morose. Mother Shipton. 



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 Pond's Extract is a certain cure for Hsmorrhoids. 

 Pon.i's F.itract is a certain cure (or Neuralfric paiiu. 

 Pond's Extract will heal Burns and Wounds. 

 Pond's Extract will cure Snrains and Bniispa. 



Sold by all Chemists. Get tbe geDoino. 



