March 20, 1885.1 



♦ KNOWLEDGE 



247 



refers to, I am incompetent to form any opinion as to its correct- 

 ness or incorrectness. Ed.] — RoirELi.-r.VKK Litkiubv Societi'. 

 Received, unfortunately, too late to be of any use. — Cov.mkxtator 

 wishes to correct a misprint in liis letter (1(510) on p. 17S. " Tho 

 raase, the cause of soul," shonUl be, '' The cause, tho cause mij 

 soul" (Othello, act 5, scene 2). lie further complains that "but 

 reason's growth " has not capital initial letters, and that I AM is 

 not printed wholly in capitals. — Wm. H. Sto.\e. Koturned with 

 thanks. You seem to be unaware that a Commission was appointed 

 in lSl>5, which e.xhaustiTcly investiirated the ijuosiion of our British 

 coal supply. See pp. 291 to 320 of " The Burdirland of Science," 

 by the Conductor of this journal. — A. E. W. Tho rubbers of a 

 plate-glass electrical machine have conducting surfacp.^, and are 

 connected by strips of tinfoil with the negative conductor. Arrears 

 of matter have so accumulated (and continue to aocunuilate) that 

 I can ^ive no guess as to the date of appearance of any series of 

 articles. A pood deal on the subject appears in our earlier volumes. 

 — Key. \V. Fitzgek.\ld. You may gather my own opinion of the 

 letters to which you refer from my reply above to E. D. (i., and I 

 feel sure will not misinterpret my refusal to insert yours. — F. 

 CoXMox. It was my own obtuseness which prevented me from 

 seeing that your letter was, in the words of the lamented 

 Artemus Ward, "rote ironikle." — TnoM.\s Ayebs. If you can 

 separate solar light from heat in rays of the same refrangi- 

 bility, you ought to be elected F.R.S. immediately (or sooner). — 

 Will An E-VBXS.«t Thinkeb kindly send his name and adilresis to this 

 office? A poem entitled, "The Blessed Hope" was left hero 

 endorsed " An Earnest Thinker," and I, perhaps not wholly unnatu- 

 rally, took this to be a gift from the said " E. T." to myself. Xow 

 I get a letter from " Commentator" saying that he wrote tho poem 

 and sent it here /.^r the " Earnest Thinker." If this is not a 

 muddle, in popular parlance, "I'm a Dutchman! " — J. A. E. G. I 

 hear of the instrument you speak of for the first time, and am 

 atterly ignorant of its use. From your description it would seem 

 to be a differential thermometer rather than, in any legitimate 

 sense, a photometer. — W. K. Kfi.vxan'. The calculation of the 

 details of the ocenltation of a fised star by the moon for any given 

 locality, with anything like accuracy, is most operose, and merely 

 impossible to be popularised. You may, though, consult with 

 advantage Mr. F. C. Penrose's description of his graphical method 

 of approximately predicting this phenomenon, published by Mac- 

 millan & Co. — Edwd. A. Tindai.l. It was the late General Short- 

 rede who first called my attention to the fact that the contraction 

 of a myo[.«j pupil lengthens the sight. Being myself short-sighted 

 I have experimented on this subject by interposing a card pricked 

 with a pin-hole between my eye and objects utterly undistinguish- 

 able from being at too great a distance, with the result that the 

 minute aperture enabled me to focus them fairl3- sharply. 

 albeit the loss of light was enormous. This disposes at once of 

 yonr idea that it is the mere increase in the amount of light 

 passing through the pupil of a short-sighted eye that improves its 

 definition. Surely you have some myopic friend upon whom yon 

 can experiment with a perforated card, and by watching his pupil 

 as he reads a page successively indifferently and brilliantly lighted r 

 Short-sight, I take it, arises from actual deformity of the eye-ball. 

 — W. Uppebtox. Whv not draw the " coal-sack " for yourself from 

 Map Xir. of the " N'ew Star Atlas," by the Conductor ?— A. F. 

 OsBOEXE. I exclude your logical and interesting letter with 

 regret J but the discussion is now closed. — Bakxaru Thomas. 

 Because of the very considerable perturbations she undergoes, and 

 the irregularity of her orbit. Why it is not even a re-entering 

 curve — in other words, at the end of a syuodical revolution she 

 is not in the same part of the sky as she was at the beginning of it. 

 — E. L. G. Forgive me if I say that I cannot aiiord you the space 

 here to air your fad about the production of geological changes by 

 comets. Of course, we have run through comets (and shall do 

 again) with as much, or as little, result as would accrue to you 

 were you to walk out when a slight evening mist was rising. 

 With regard to your benevolent efforts to instruct the Cieikies, 

 Eamsays, Lyells, Ac, I would simply repeat the beautiful words of 

 the poet: — 



" Teach not a parent's mother to extract 

 The embryo juices of an egg by suction ; 

 That good old lady can the feat enact 



Quite irrespective of your kind instruction." — 

 R. Oakley. Do you seriously imagine that you will obtain admis- 

 sion solely on the merits of your inventions ? — J. B. Rcxdell. I 

 should prefer to wait until it has undergone the criticism of experts. 



Hexey J. Weight. Even were the discussion not closed, your 



letter adds nothing to the controversy, with its introduction of the 

 exploded figment of a "vital force." It would be as sensible to 

 speak of a " watch force " as a distinct entity. On receipt of a 

 stamped and directed envelope, your MS. shall be returned to yon. 

 — Holmdale. Premising that 192,000 miles per second were 



spoken of as an erroneous measurement of the rate at which light 

 travels, and that its actual velocity was given as li^G,771 miles in 

 a second, jierhaps your dilliculty will disappear if you rclloct that 

 light consists of undulations or vibrations in something which fills 

 all space, and which is called tho a)ther ; .and that it is not until 

 such vibrations are transmitted to the retina that wo see anything. 

 Drop a stone into the middle of a liirge still lake, and a very appre- 

 ciable interval will elapse before the tiny and ovur-diniinishing 

 waves thus generated beat upon the shore, the stone having been, 

 for tho greater part of that interval, safe and sound at tho bottom of 

 the water. Suppose that the light from a fixed star occupies ten 

 years in travelling to tho earth. Then, quite obviously, if such an 

 orb came into existence tonight, wo could not possibly see it for 

 ten years to come. After that, light would continue to reach us 

 unintermittently as long as ll:o star remained in existence ; but we 

 should, of course, see tlie star, not as it was at the instant we were 

 regarding it, but as it was ten years before, when the light left it. 

 For the same reason, were it annihilated, tho light which loft 

 it at tho instant of its disappearance, would reach our 

 eyes ten years hence, so that we should continue to sec 

 it shining in tho sky ten years after it had absolutely 

 ceased to exist.— WAnuiiEir. The oBi e of Kxowlepge is in 

 Great Queen-street, London, W.C., and not in Queen Victoria- 

 street, E.G., a totally different locality. — Halt.yards complains that 

 in letter liJ2o, p. 203, lino six from the bottom, " firearms, language " 

 appears, when he wrote "tire, arms, language," and that on the 

 ponultimaie lino " this subject " is printed for " their subject." — 

 S.S. The details of precession and nuiution scarcely admit of 

 popularisation, but if any considerable number of our readers should 

 express a wish for a popular general account of those phenomena, 

 I shall be very glad to give it. — W. B. The " blessed Marchioness " 

 of whom you speak as "capital padding" will disappear from 

 these pages at the conclusion of the series of dialogues in which she 

 is an interlocutor. Xo, neither " end of the wedge," either " thin " 

 or thick. The lunatic you refer to sent me a publication which he 

 edits, and that was my way of letting him down easily. If I did 

 (as you allege) " dote on that personage," I must be in my dote-age, 

 with a vengeance ! Sorry that your " useful formula" was crowded 

 out. Here it is : " A penny a day = f 1 -l-fj -t-either 5 or 6 pennies 

 according as the year happens to be an ordinary one or a Leap 

 Year." With reference to the paragraph which has elicited your 

 approval, I only said what, I fancy, everybody else thought. You 

 are mistaken in your supposition that I shall not insert what you 

 tell me because I shan't believe it; for I shall insert it, and do 

 believe it; a precisely similar case having come to my own know- 

 ledge. Hence, when yon state that at the age of thirteen or four- 

 teen, you distinctly saw Mars with the naked eye as a clearly- 

 defined, red disc, without rays or any irregular irradiation, you are 

 describing an uncommon, but by no means unique, occurrence. — 

 W. Gray. Delayed for several days, owing to your having ad- 

 dressed 3-our letter to the Editor instead of to the publishers. The 

 Editor has as much (or as little) to do with selling numbers of 

 Kxowledge as the Grand Llama of Thibet ; there or thereabouts. — 

 Rev. Leoxard H. Eudd. You will note an excision in your letter 

 as printed. To have reproduced the paragraph which I have struck 

 out would have been to invite, with absolute certainty, rejoinders 

 which, in common fairness, I could not have excluded ; but which 

 could only have initiated a Siscussion at once unprofitable and con- 

 trary to the frequently-expressed and absolutely inexorable rule 

 which I have laid down, with reference to the subject you attempt 

 to introduce. — Hallvards. Kindly read the reply which I have 

 just written to Mr. Eudd.— E. Norris. I must reiterate, for the 

 nth time, that Knowledge cannot be supplied, "free of charge," 

 to any reading-room, clnb, library, or literary association whatso- 

 ever : an answer which I must ask Alfrkd Cotgke.ave to accept 

 too. — Novice. The wind is said to "back" when it shifts in a 

 direction against that of the sun's diurnal motion ; for example, if 

 it does so from S.W. through S. round to E. and N.E. It " veers" 

 when it shifts with the sun, say from S.W. through W. to N. An 

 anchor is " foul" when the cable gets twisted round it in any way. 

 The third yards of a ship, counting upwards from the deck, are 

 "top-gallant yards." "Courses" are the square sails next the 

 deck, i.e., the mainsail and foresail of a three-masted ship. A ship 

 lying-to in a gale drifts a little, but practically does make no way. — 

 G. n. Daxx. I have delayed the acknowledgment of the receipt 

 of your letter for a fortnight, expecting the arrival of the photo- 

 graph which, you say, accompanied it. As I have seen nothing of 

 this photograph, however, I think it is now quite time to tell you 

 that it has never been delivered. 



Messes. Walter T. Glovee & Co., of Manchester, have secured 

 the contract for the wires and cables reriuired this year by the 

 Commissioners for the Lighting of the International Inventions 

 Exhibition. 



