2S4 



♦ KNOWLEDGE 



[Sept. 



9n^trs( to Contscponlirntst* 



/Wr A# TJii4>r rt^trimf farlf 



$koutd rracA A« 



(if EnOWLBDOB^ fJbtf 

 4 r<irfy m tkt «rr«lr. 



tmij /or teUntyic im/ormation 

 ti* Editor/or eorr^tpondemt* 



of' corrt$pondent» i' , ' 



.11, 



■^trtnci tAomtti 6« i 



M(<r ftovU Ikart a Hilt, and 

 number, th« pagt on rAicA i7 



SiMi'tES wishes to know if Bayma's Molecular Mechanic 

 \» (till ill tyjie, and what works, if any, have been published since 

 on " the theory of eimplo elements." — J. T. Hinton. There is 

 certainly :i mistake in the passngo quoted from Ferguson. See 

 replies on the subject. — Iota. A September transit of Mercury is 

 impossible, becaoso when Mercury is in inferior conjunction in 

 September, he is not near a node of his orbit. Ilis longitude when 

 he is in inferior conjunction is the same as the earth's ; and as she 

 passes in September from longitude 338° to longitude 8° (roughly), 

 whereas Mercury's nodes lie in longitudes 45° and 225" (ronghly), 

 a transit cannot possibly occur in September. — T. H. Laing. It' is 

 not a " new discovery " that 0"* is not equal to ; 0^'= (4)', that 

 is, is equal to infinity squared. Substitute x instead of for Cr' 

 in your siiphism, and where is it I" — E. Wii.so.N. Do Morgan's 

 " Book of Almanacs." — J. Uimmikk. Do not know where there is 

 any transhition of Prof. Virchow's address on "The Liberty of 

 Science."— Cossios. Thanks. I wos away fnjin town when p'roof 

 reached me, too late for return. Transit shortly.—W. liRowN. 

 That promised work appeared several years ago under the titlo 

 "Geometry of Cycloids" (including Trochoids, ic, ic), publishers 

 Ixmgman 4 Co. Price 10s. Cd. I cannot speak confidently of any 

 books on geometry U-yond ordinary course of Euclid, Solid and 

 Conic Sections, ic, not r|uito kno«-ing whether you include analytical 

 books. Have you read Salmon's books on Conic Sections, and 

 the Higher Plane Curves, Frost and Wolstenholmo on " Solid 

 Geometry "? (Both analytical, however.) Between ourselves, 

 I have not been a great reader of mathematical books. When 

 a mathematical difficulty, outside my reading, occurs to me, I 

 generally invent my own method of dealing with it. Hence I am 

 about the last person in the world to recommend " a book or books 

 in English. German, French, Italian, or Spanish." That old edition 

 of Euclid, by Isaac Barrow, shoold be full of interest to a geome- 

 trical student.— E. A. Browx. I most heartily thank you for 

 your kind and encouraging letter. — P. Binyon." Many thanks, 

 but at present we are "choked" by matter standing over, and 

 Jevons* logical alphaljct could linrdlv find space.— E. 8. B., E. K. 

 Rai.li.vo, a. W. Tillktt, J. TiionAsi John Tiiom.son, C. Hahiiis, 

 E. O. H. Thanks. — R. P. Tvi.eb. If there were no nir, a ship or 

 other object would be depressed eight inches below horizon plane 

 ■when she was a mile distant, four times as much two miles away, 

 nine times as much three miles awoy, and so on. But, owing to the 

 refractive f»ower of the air, the depression varies (according to 

 state of the air) from about six to about seven inches per 

 mile. Calling this deprexsion <£, the depression at a distance 

 of n miles is n* d. — G. T. Rtvm. I would insert your letter 

 if it were not quite so long. Our arrears increase, desjiite 

 all wo can do to keep them down. Pray excuse mo on 

 that score. As for temjjtrance, I think the tone I have taken 

 ha^ 1 . . ii r r, ,.. ,];,i^.;., n]</derato. I take, in reality, much the 



I Mr. Williams — wo neither of us are tee- 



■ 'ul>erant honesty (which, like all virtues 

 n. "vice" — vide Webster, Worcester, and 



..ho calls his moderate use of wine or 



!/• • r ii I'm;. IT .1 >iic, whilo I do not, you may depend there 



is no real difference of opinion between us as to tho use of 



•timnlaot*. Anyhow, ho is going shortly to give hia views 



h'Ti-. in full. I must have expressed myself very ill, if I 



'liBt Mr. Williams's own word's camo near humbug 



lint, if any one tells another who is taking 



■I I'i Ntimulant that he is foolish or vicious, then I 



[Kxrii.y. The nrgnment from mortality statistics 



II men ore separated into two clasncH, those who 



iri.m liquor, and those who do not so abstain, it is 



• .'.rt.'.lity will bo greater in the class of non-ah- 



' r. This needs no pr'»of ; but it can i)rove 



'^ moderate use of stimulants. It might 



.•ii.tic« you quote show, that if men were 



• 'lasses, ranging from total nlMtainers to 

 ii.v. Krr.t'- "iriiiikiir'li', the mortality would be found gradually to 

 diminish till we came to a class of men like AbW Moigno, 

 Mrjihiato, and " my learned friend," who took some small allow- 



ance, and thcuco grndunlly to increase till tho topers wore roaohrd. 

 — SwiuMiNG. Try wadding, soaked in oil, for tho ears when 

 swimming. — H. Tate. Your theory will not explain curved tails. 

 — J. A. Ollahu. Thanks for tho stories, for which I will try 

 to find i-ooni, but fear may not be able to. As to the dates, 

 unfortuuately, as soon as wo have got ouco round, we loso 

 all wo had gained, or regain all wo had lost. — E. P. B. 

 Hak.ston. It is said to bo proved (which only proves it 

 is said) that two ships on a calm sea approach each other. 

 Theoretically they should, as they ore bodies having mass, and, 

 therefore, attracting each other, but so slowly that a lifotiino 

 should pass before they collide.— Cahb. Fkk. Can find uo trace of 

 missing query. Index long since ready. — Co.nstant Ueadkk wants 

 to know which are best books for study of zoology, whether thoro 

 is a zoological society in Liverpool, and if a Liverpool clerk can 

 become a U.Sc. without leaving or giving up his situation.- - 

 U. B. Tho snow does not withstand tlio blazing boat. It molts 

 " like anything." I have boon there, and know. — A. 11. MonsoN. 

 See abstract of Sir W. Thomson's discourse in our columns. Tho 

 Times report, followed by Engliah Mechanic and other paiiors, alto- 

 gether too absurd. — J. Watson, Jun. I do not know Todhuntor's 

 smaller Algebra, but should imagine it would suOice for your 

 juirjioso. If you got the larger you should leave out a great deal. 

 The chapters on Infinite Series, Continued Fractious, Probabilities, 

 would be of little use. Spherical Trigonometry is essential for tho 

 study of theoretical astronomy, though much iu Todhunter's book, 

 small as it is, can be omitted. Tho elonionts of tho Differential 

 Calculus — really as easy as Algebra or Trigonometry— should also 

 be studied, as you advance. — A Reaher desires to know which ia 

 tho best work on Logic. — Bkoinner, ditto for naming specimens in 

 Jlerbarium (cheap book). — W. Mackwoktu. Cannot undertake to 

 forward geological specimens to authorities on tho subject. — 

 Obion (1) All solid food, I fear. I cannot vouch for the value of 

 the remedy. It seems heroic, hut Orion was a hero. (2) Tho 

 property may bo thus proved. Let tho digits of a number, N, bo 

 Pii Ps. Ps. *e., p, being in tho units' place. Then N=Pi-f lOft-t- 

 lOOijj-hlOOO Pi+&c., and if n bo tho sum of tho digits pi, jij, ic, 

 then 



N - u = 9pj -t 99^3 + 9P9p4 + &C., 

 a multiple of 9. — J. Ghkenfield. Only admitted for tho sako of 

 argument; there is nothing in nature to show it likely, or oven 

 possible, that solor undulations can return in any form. — H. AuiiREY 

 lIusHAND. As much heat is added as would bo required to raise tho ^ 

 quantity of rain which has fallen from tlio form of water to that of 

 a<)Ueous vapour. But, as btatcd, the jjroblom is not sufficiently 

 definite. We must, however, deprecate the sending of problems to 

 us, easy or difficult. Tho solution of problems is outaido our pur- 

 pose. — Geo. Cbaio asks whether a friend of his is right in saying 

 " that London Bridge had been lit up by tho cliHlric light, but was 

 discontinued on account of the restive cuiidilion t>f the horses." 

 " Is this correct," ho asks, " as applied to London or any other 

 bridge ? " — Slasher. Slash away, to your heart's content, at us, 

 but not at poor old Horace. What has ho done that yon should 

 cut him uj) as you do? Wliat Horace says is not "that noblo 

 hexameter " (!) 



ifulato nomine dc tcfahula narraivr. 

 It is enough to make him turn in his grave, if ho had not already 

 turned (into dust), to alter bo his familiar 



.... mutato nomine de ta 



Fabula narratur. 

 A. B. C. Does not the difficulty arise from taking a case where iV 

 does not vanish, and in treating it, putting SU = 0? — T. A. (1) Yos; 

 rain often falls after a ligliliiing Hash, often so soon after as to 

 suggest (considering how long tho rain must have been falling) that 

 the rain began to fall before the lightning Hash was scon. (2) It 

 is the case that in explosions there is condensation anilacoiiHiqiKiit 

 rush of air towards tlio scene of tho explosion. In a great exjilosion 

 which occurred at a rhemical factory in France, the windows woro 

 all blown inwards. (3) Have forgotten my reply to U. Askew, and 

 subject of his question. May I ask you what it was about ? — A. K. W. 

 Seeing how our corrospondenco is overflowing, you will understand 

 and forgive my inability to insert your rather long letter about Mr. 

 Williams's views and " Mr. Editor's." You overlook one point. You 

 speak of tho indulgence in an occasional glass for other than medi- 

 cinal purfioses as "doing no g'Hjd," though you speak of it aa 

 "giving pleasure." Is the pleasure (if not hamiful) no good? 

 Surely it counts for Boraething. For my own jiurl,, looking back 

 over my past life, I repent mo (l can use no other word) for every 

 missed opportunity of taking pleasure, innocent to myself and not 

 harmful to others. Moreover, I believe the df>c( rine to be a most 

 wholesome one, and calculated to gri^atly increase tho hapjiiness of 

 the human race, both directly and indirectly, that, when we are 

 morally certain a pleasure will neither barm ourselvoa nor 

 others, it is a duty to take it. Tho energy devoted to 



