JtJLY 14, 1882.] 



KNOWLEDGE ♦ 



119 



misunderstand him. They might imagine tliat all four-footed 

 animals are mammalian, or that all mammalians have either four 

 legs, or (like man) four chief limbs." 



(2.) " Dr. Wilson seems to imagine that all fom--footcd animals 

 are mammals, and all mammals four-footed. Will he permit me to 

 inform him that this is not the case. A crocodile has four feet, but 

 Dr. Wilson will tind, on further examining the subject about which 

 he writes, that a crocodile is not a mammalian. Man, on the other 

 hand, is a mammalian ; but man cannot be said to have four feet, 

 although during a portion of his existence he goes on aU-fours. 

 Nor can the whole, though a mammalian, be properly called a fonr- 

 Icgged animal ;" and so forth. 



" Post-card" seems to think the writers I mentioned have com- 

 plained to me of such patronising communications as the last. This 

 is not the case. In only two cases (I introduced Mr. Grant Allen 

 only by way of illustration — no one has yet explained botanical 

 matters to him) have contributors had occasion to make what I 

 consider the right sort of answer to letters of the kind. This they 

 did, without any reference to the matter in writing to mj-self. lint 

 then came letters to me from the carpers, angrily denouncing 

 me for poking fun (which I had not done) at writers so 

 thoroughly [acquainted with " the quartile character of two- 

 fold duality." I may adil that, in his imaginary illustration of 

 Mr. Grant Allen '■ attacked by a critic," "Post-card" speaks 

 as if the article on Hesperoriiis, &c. ("Birds with Teeth") 

 in No. 2, were from Mr. Allen's pen. I feel able to assert 

 the contrary, having, to the best of my recollection, written 

 that article myself. To " Post-card's " conclusion, that only pro- 

 fessors should correct the statements of professors, I entirely 

 demur; that is just the sort of thing against which Knowledge 

 sets itself, — the cant and humbug of specialism and officialism 

 (specialism being, however, an excellent thing in itself and when 

 free from cant, otficialism necessary, and not bad when free from 

 humbug). — Ignobamls. Cold weather of June may be capable of 

 explanation, but it certainly has not yet been explained. — W. 

 Benson. We saw many other objections, quite as serious, to your 

 theory; but the one we quoted came first to hand. How would 

 you exjjiain multiple tails, curved tails, side tails, cross streaks, and 

 the like ? — LieijT.-Col. Boss. Eegret to find you have in so short a 

 time entirely changed your views. You think that (1) Knowledge is 

 diminishing in circulation (oddly enough, only three days before 

 your letter came, "the largest weekly sale since we started" was 

 announced to me) ; (2) that it ought to diminish in circulation ; 

 (3) that its so failing is due to the delay or omission of your 

 articles (you do not say so in so many words, but imply it plainly 

 enough). You point to the Exchange and Sixpenny Sale notices of 

 volumes of Knowledge for sale as proof of this. The proprietors 

 were flattering themselves that these notices resulted from their 

 own announcements, though they want rather the first seven back 

 numbers to make up volumes than to buy back complete volumes, 

 which onr new subscribers will willingly do. It may interest yon 

 to learn that all the volumes originally in stock have been sold, and 

 that of others made up with numbers bought back, only seven 

 remained in stock a few days ago. — A Stcdent. You rather sur- 

 prise US; for Mr. Hume's view has been expressed even more 

 strongly by medical men of experience. — SctKNTU. Medical men 

 would probable advise you not to sit up reading till one. Whether 

 you can do so or not, without injury to your eyes or body, depends 

 on circumstances which only those who know you well personally 

 can bo acquainted with, on your constitution, habits, eyesight, &c. 

 If you neither drink nor smoke, and your food is usually plain, 

 reading till one should not hurt you. But if you find it necessary 

 to take strong coffee or tea, or "to bind your head with wet cloths 

 or the like, yon may rest assured you are injuring yourself. I can- 

 not myself advise yon, <)nite in the dark as I am, nor allow anyone 

 else to advise you through these columns, to what nn'ght bo very 

 good for A, B, C, F, and G, but very bad indeed for D (yourself, 

 let us suppose). On the other point, I do not know; but 1 fancy 

 that no societies meet on the dates you mention. — Alirep. The 

 solution would run sonu'what as follows, I suppose : — 



1 4 



Sec. 



(l,t,6,3, recurring) 



Ls 8» 8' 8'J L 



8'h 



i + .I.S'-l-G.S + s/ -^ \ 



_819/ 8' \ 

 ~ 8' U'-l/ 



819 ^1 

 lOl'S 6 



A. McD. Have forwarded your question to Mr. Grant Allen. I 

 quite agree with you that the handkerchief shows on a London fog 

 day, that it is better to breathe through the nostrils ; but not that 

 blowing the no.se is a bad habit. The mucus does not act aa an air 

 filter. The irritating action of the matter which has been filtered 

 out of the air causes the How by which mucus is formed, and so the 

 particles of carljon, &c., get in the way of being removed, preferably 

 by the process you think objectionable.— W. Southall. Thanks; 

 but the mistake is tolerably obvious. Our contributor wrote 

 " Decoction or tincture of Cinchona," which was misprinted 

 " Decoction of tincture," Ac. He added on proof a marginal note, 

 the last word of which was "quinine," but struck it out; unfortu- 

 nately the last word seemed to remain unscorod out and was taken 

 as a correction for Cinchona. We have forwarded your note. 

 There is,|of course, no objection to your correction ; on the contrary 

 wo thank you ; still, you should hardly have supposed that anyone 

 could be ignorant "of the fact that " decoction of tincture 

 of i|uliiiii", " .iiiil " ilrcoction or tincture of quinine" would 

 ci|ually I II II . ii-r. A correction of an obvious "printer's 



error" \v il 1 I.;. • I ii more acceptable than one implying a 



simply riili.uiuiis, auil, in fact, impossible blunder. — T. Moecak. 

 A number of correspondents object to the blowpipe articles, which 

 for that and other reasons have now come to an end. Bnt, as I 

 learn from Lieut.-Col. Ross that you are in correspondence with 

 him about a pyrological society, you can readily find other and 

 better ways of announcing the 'plan to pyrologists.— Eve-witness. 

 We will convey to Mr. Allen and the author of " The Amateur 

 Electrician" your suggestions about illustrations, but you must 

 consider onr smnll rri'-" -ivA ''i.^ absolute necessity that expenses 

 should be kept .1 ■. i: '11 t' > -i -wtli of our circulation has continued 

 some time long! r \ , i • once do what you suggest if we 



made the price tin ,:; imber. We prefer waiting till we 



can make such im I I i Imut increasing the price. Already 



wo have gone, ill I i use (especially for original matter) 



far beyond what i i i i I iicsent circulation justify, encou- 



raging though tin lii 1 ,1! n iy is. It is «o( very encouraging 

 to find our efforts in tlie way of cheapness altogether ignored as in 

 your letter. — B. M., F.B.C.S. Some singular experiences in my own 

 family circle confirm that view. But I do not care to cite them. 

 — B. M., F.R.C.S., wishes to know where the mild tobacco mentioned 

 at p. 79, letter 415, can be obtained.— Ecoxomkst. Suggestions 

 noted.— W. Peddie. Thanks.— J. R. C. Thanks; but we have 

 given general solution for case of belts not crossing — understood in 

 the problem. When they cross, solution is similar, so far as geo- 

 metrical principles are concerned. — H. C. Floyd. The geological 

 structure of that spot is well known, and will probably be referred 

 to by Mr. Harrison in the course of his papers. — F. Cowley. No ; 

 you cannot muUi] ' :■• ' iinney. In the case of foot by feet, 



all you can sa> i- : i.f feet in the length multiplied 



by the number : i a rectangle, gives the number of 



square feet in tl is not multiplying feet by feet, 



however.— J. B. Siiiriiv. Thank you; but that way of doing the 

 Fifteen Puzzle would not be of use to our readers. 



CHEMICAL AMSWEBS. 

 QUEKIST.— Pure quartz does not lose weight by being heated alono 

 (hydrous varieties lose water) ; in a current of steam, however, it 

 slowly volatilises. If the mineral be powdered and fused, its specific 

 (irarity is altered ; that of crystalline quartz is 2T>, after fusion it 

 becomes 23. The same change takes; place without fusion if^the 

 mineral is kept for some hours at a temperature of about 2,000* C. 

 This lighter form is also found naturally, but only rarely occurs 

 in crystals. When it does so it receives the name of " Iridymitc." 

 These differ in shape from the crystals of quartz, and belong to 

 another crystallographic system. 



MEDICAL. 

 " A beadeb op the Same " had better go where ho can got plenty 

 of exercise on elevated ground— the Yorkshire Wolds, the Sussex 

 Downs, Firth Hill, &c.— avoiding valleys for residence. He should 

 have a pursuit, whether it bo geology, botany, or any other study, 

 which will necessitate out-of-door exercise. He should clothe so as 

 to avoid chilh, and leave oft all spirila. Aa to the Turkish bath, ho 

 should consult liis medical man. A dose of Carlsbad salts every 

 other morning will help him. 



IMPROVEMKNTS IN THE Rl'nnKH.'i OP ELECTRIC MAiniNK.".— By O. 

 J. Agostini.— Very fine clmrcoal-powder is rubbed up with petro- 

 leum to a tough liquid, and spread with a brush uix>n thin cotton 

 paper. The surface of the ordinary rubbers is covered with strips 

 of this paper. Tliey arc not hygroscopic ; give a good development 

 of electricity, and cleanse the disc— IVicdmianirs Briblatter. 



