Dec. 16, 1881.] 



KNOWLEDGE 



139 



Xetttrsf to tt)t eiiitor* 



[The Editor doei noi hold Mnuelfretpoiwible for the opinions of hit correspondent*. 

 Be cannoi undertake to return manu$>:ripts or to correspond tcith their Kriters. All 

 ccmmumrafiOMt thould be a» ahort a* poenbU, <:ontiigfently Kith full and cteur state- 

 menit of the vnriter'g m^an\n(i.'\ 



All kditorial (^mmunicaiiont should be addretseJ to the Editor qf KnOwi,bdgb; 

 (,n Sueinesa comnunicutiona to the Publiahera, at the Office, 7-i, Great ^uem- 

 ftreet, W.C. 



All RemittiTtice.*, Cheque/; and Fofi-Office Order» ahovM be ntade payabU to 

 2t£egara. ffyin<in Sr Sana. 



'^•All tHtera to the Editor tnll be Kxtmherfid. For comenience of reference, 

 corretpomtenta, when r^errxng to aui/ Utter, kHI oblige by mentioning its numher 

 and the pa^e on v\ich it appear*. 



All Lett'era or (Queries fo the Editor tahifh require attention in the current issue of 

 KyovrtJiDGii,rhould reach the Publishing Office not later than the Saturday preceding 

 the day qf publication, ^ 



"In knowledge, that man only is to be contemned and despised who is not in a 

 state of transition. , , , , "Nor is there anything more adverse to accuracy 

 than fixity of opinion." — Faraday. 



"There is Do harm in making a mistake, but preat harm in making none. Show 

 me a man -who makes no mrstakes, ana I ynlX show you a man who has done 

 nothing-." — lAebig, ______ 



<^m Corrrgpontrnice CoIunutEf. 



DEMANDS OX OUE SPACE. — CURIOUS PUZZLES. — 

 GRAMMAR.— CEKTKTTrGAL FORCE, &c. — A PARABLE 

 FOR PARADOXERS. — THE EARTH'S PROCESSIONAL 

 REELING.— ILLUSIONS.— BRAIN AND SKULL.— MAR- 

 RIAGE AND THE DEATH-RATE. 



[121] — A coiTespoiidciit remarks, and with eojne justice, on 

 I he spare awarded to correspondence, queries, and replies to 

 iicriea in No. 6. It is natnral that in the first number of a 

 nngnzine admitting coiiespondence at a)l, the siiace devoted to 

 ;iL-h matter should be nnich Icbs than in later numbers. As 

 I orrespondcuce (iucludin? notes and queries) was mentioned in the 

 prospect U.S, I caunot consider ihat the increase of this section in 

 Xos. 2. 3, Ac, was inconsistont with o\ir promises. But, while 

 noting this, and that, indeed, number 6 was enlarged to.obhgo 

 correspondents, I must admit that it would not do to allow cor- 

 respondence often to occupy so much space. As letters come in 

 more and niore freely each week, and as we hare not room for more 

 than a third of them, it ia clear that two-thirds must be oraitted. 

 Those that are most (U'iginal and interesting will naturally have the 

 l'"st chance of being ret:iino(l, and among these the concise will be 

 ipfenvd. 



Some Icilcr.^ will be ^ivc-n iu abstract, with, Such reply a.s may 

 ^■cem necessary, in a w.fwkly cimimunication from '' the Editor." 



" H. A. S." notes that tliere is. an e.^hauativc solution of the pro- 

 Heui of tlie Fifteen Schoobgirli, in the " Ladies' aud Gentlemen's 

 Diary " for 1862. Mapii' .sijuarcs are treated fully iu Hutton's 

 "Mathematical Recreations." Nevertheless, I tiiink the tliree 

 letters on these two subjects published in this or following numbers 

 will interest many who would not care to look up the above-named 

 writer. They may suffice, however, for matters which are rather 

 curious than scientific. 



"L. F." remarks (see " A. T. C.',s" letter, 103, p. 117) that 

 ■would the editor" is more deferential thau "will the editor," 

 "might I" less manly than "mayl,""l caimot but think," " I 

 <au but think," and " t can only think " equivalent expressions, 

 lie notes justly that such a sentence a.s " the editor requests that 

 ' tters may be addressed,' is inconeet. " May " should be omitted. 

 Ibe same with "he requests that all communications (should) be 

 addressed," Ac. "should" should be left out; or, better, "he 

 requests that " shoaJd bo left out. We have under our corre- 

 spondence heading " he requests thai all commnnications should 

 be as short as possible." PHsewhere in our remarks, be it noticed, 

 we adopt the correct form. Perhaps we meant to say editorially, 

 " we request that the ))innciple be adopted ' all communications 

 should be as short as possible.' " We take " L. F.'s " hint, howerer, 

 and put this principle down definitely as one which we are obliged 

 to insist upon. 



Mr. Newton Crosland is, I fear, offended because I have said that 

 he misapprehends the principles on which the accepted theories 

 which he opposes are basod. I am very sorry. I have no wish to 

 -offend him. I have simply stated the facts as I see them. He 



describes the'ccntrifugal force in terms entirely inconsistent with the 

 real nature of this so-called force. (He is quite right in saying 

 that Newton spoke of the centrifugal force; so also Newton spoke 

 of the force of inertia. Newton, however, carefully distinguished 

 those from " impressed forces." Modern science, to avoid precisely 

 such misconceptions as Mr. Crosland's, ceases to nee the term force 

 except in the case of ivhat Newton called an impressed force. 

 Joyce, Milman, and Ferguson are not anthorities in such a matter, 

 not one of them having had any masteiT of the higher mathe- 

 matics. ) Again: Mr. Crosland. in dealing mth the Darwiniait 

 theory, uses words only applicable to the Lamarckian hypo- 

 thesis. A student of science knows the Newtonian theory 

 and the Darwinian theory, attacked by him, to be unlike 

 what he supposes ; .ijid, therefore, is justified in saying to 

 him that very likely these theories, so misunderstood, appear 

 egregionsly absurd. And there the matter should end. I am 

 not interested, aud I am sure readers of Kxowiedre would not 

 be, in defending the straw-giants which Mr. Crosland attacks after 

 having constmcted them. But there is nothing which need offend 

 him in the remark that he misunderstands the teachings of Newton 

 or of Darwin. Many minmderstaiid both. Of the former, at any 

 rate, which belongs to my own ' special department of study, I may 

 say that few understand them. Many who understand the Dar- 

 winian theory, reject it, or regard it as so far not perfectly proven. 

 But no one who imderstnnds the Newtonian theory questions its 

 truth. Any one who, understatiding it, yet objects to the former 

 theory, will find his reasoning admitted here. Any one who does 

 not understand any particular point about either theory can ask 

 bore for explanation. But all our space would be wasted if we 

 allowed correspondents— first, to set np burlesques of scientific 

 theories; secondly, to overthrow these shams ; and, thirdly, in the 

 triumph of an imagined victory, to invent vagtie theories of their 

 own, in establishing which they assign to imaginary forces incon- 

 ceivable effects. 



A chemist iu New Zealand once asked me, as a believer in the 

 Newtonian theory, how I explained a balloon's ascending. Before 

 I replied, he went on to say that, to his mind, the ascent of a balloon 

 proved that the earth exerts a repulsive as well as an attractive 

 influence. There was a pair of scales on the counter, in ono of 

 which I put a half-ounce weight, and as the other scale went up, 1 

 asked if its motion was due to terrestrial repulsion. " The cases arc 

 different," he said. " The cases are similar," I answered ; "the light 

 scale ascends becansc the heavier one has a greater tendency to de- 

 scend, and cannot descend unless the light one rises ; the lighter gas 

 in the balloon ascends (taking its silk coat along with it), because 

 the heavier air around it ha.s a greater tendency to descend, and 

 cannot descend nnless the lighter gas rises. The heavier scale pulls 

 up the lighter, which would else tend downwards ; the heavier air 

 thrusts up the lighter gas; which would otherwise descend as cer- 

 tainly as a globe of lend would." Whether the chemist understood 

 or ac<?epted my explanation, I do not know ; but this I know, that 

 if he had based on his misapprehension of the effects due to gravity 

 a theory of polarity and magnetic repulsion, I should not have felt 

 lidund to discuss his ViSws vvith'biWt. In a similar way. acting-^'"'^ 

 iiccordiiig to my lights, iihd with the object of occupying the columns' '• 

 of Knowledge .so as best to serve the wants of readers, I must', 

 decline to assign inortfthttn a'vfffjf'ih'ddest allowance of space here' 

 to I iaradosi(?al theories.' " " '■•";!,;" 



"Sirius" asks for an explanation of the "Precession of thd'' 

 Equinoxes." ' As this is a subject of general interest, I do not put 

 this letter among the other queries, but reserve it for an answer ■ 

 in an early number. I note here that the change is not such as to 

 catise tho northern pole to be inclined from the sun in June 13,000 

 years or so hence. Nor is the motion of the poles such that 6,500 

 yours hence, or at any time, the, axis of the earth will be at right 

 angles to the ecliptic. The inclination of the axis varies only within 

 a very narrow range, and the seasons remain almost unchanged in 

 each hemisphere, throughout the long precessional period of nearlv 

 2.5,900 years. " i 



J. E. Okill remarks that the ""liest of illusions," p. 71, is illusive' '' ' 

 to, him, as respects tho apparent superposition of the space between 

 the t-wo hea-v^' circles, only when he expects to find an illusive 

 effect. If he looks along the h'ues as a carpenter looks along a 

 ]iieco of wood, they Seem straight, and the circles seem oval. 

 (This, of course.) He describes as an illusion what is in reality an 

 effect of diffraction. Closing one eye, look at the edge of a window 

 with the other, covering this eye gradually with the hand till only 

 a fine slit is seen, when the colours of the spectrum are displayed. 

 He remarks on letter 114, p. 121 (Brain and Brain Case), that the 

 two doctors are in agreement. Naturally, tho skull takes first a 

 form determined by the groivth of the brain, while later the brain 

 may shrink away from its bony enclosure. Also, " may it not be 

 that the son of a man noted for skill in some art or science may 

 inherit the shape of his sknll," but. forwent of stndv, the brain 



