Nov. 21, 1884.] 



♦ KNOWLEDGE ♦ 



431 



form of the so-called "brush discharge" of the ordinary electrical 

 machine. It is common enough at the mast-heads and yard-arms 

 of ships during thtrnderetorms. — Ax Ano.nvmols Corbespoxdext 

 sends me (in connection with Mr. Tindall's letter, 1500) a cutting 

 from "Industry" for May 13, 18S0, describing an eye-photometer, 

 the invention of Mr. William Ackroyd, dependent on the sudden 

 shortening of the rays from an artificial star, as the source of 

 light to be measured is approached. — Waltek G. Woolcombe. 

 Once more, Mr. Proctor has ceased to lectui-e for good and all, 

 and cannot relax this rule for atnjlody. Besides, he is not 

 iu England. — Axoxymous. Thanks for correction re p. 382. 

 It is noted elsewhere. — E. A. Tixdall. Will test the apparatus 

 when it reaches me. — Tncs. Allsop. The semi-diameter of the 

 earth's penumbra = the parallax of the moon + the parallax of the 

 Sun + the Sun's semi-diameter, I'.c. {ride p. 383), 59' 171" -<- 8'9" + 

 IC 2-4" or 1° 15' 28-4", add j'^th (say 1' loS") to this and we have 

 1° 16' 439". Now, in onr figure, the radius of the earth's shadow 

 = 44' 7" is 11 inch. Then we say 44' 7" : 1° 16' 43-9" :: 11 

 inch ; what we sh.ill find to be 1'9 inch ; so that we have only to 

 open our compasses to a width of 1'9 inch, and, putting one leg on 

 C in the figure, describe a circle round it. This will represent the 

 penumbra, the times of contact with which we shall obtain from 

 inspection by the aid of our hour-line, LN. — High Clemexts. No 

 more room to spare for details of your " Weather Cycle." — Hall- 

 yards. Nothing akin to M. Flammarion's observation has been 

 made anywhere else. He can not mean the penumbra ordinarily 

 80 called (see reply above) as it would be ridiculous to speak of 

 that as "egale i la 35'. partie de I'ombre de la terre." How, 

 though, he separated his penumbra from the real one does not 

 occur to me. Liais's observations of twilight in Rio gave a height 

 of about 200 miles as that of the atmosphere, so Flammarion does 

 not seem much out with his 224 miles, however he arrived at it. — A. 

 H. " The Herringand Sea Temperature " much too long for extract. 

 — G. D. EvAx.s. The only " Almanac Lessons " which have, so far, 

 appear, will be found on pp. 23 and 206 of our fifth volume. — 

 MrsAFiR sends a curious story of his own seeming recognition of a 

 group of deserted buildings and enclosures upon which he came, 

 for the first time in his life, during a walking tour in the Eastern 

 Alps. He heads his communication, " Coincidences," but his 

 experience would rather seem cognate with many of those related 

 in connection with the discussion over Our Two Brains. — Old Moox 

 spins an amusing yarn about being knocked up by one of the crew 

 of a schooner which he commanded, while lying in Loch Inver to 

 see " two stars " which had faUen down and pitched on the " cross- 

 trees, one on each side ! " the said stars being a couple of 

 " Comozants " (vide reply to J. Ferguson above). — Chas. Rice tells, 

 at considerable length, how his drowned brother was resuscitated by 

 a man who inflated the boy's lungs with his own brandy-laden breath. 

 Many have been recovered in similar cases by artificial respiration. 

 The brandy had nothing whatever to do with it. — H. S. S. I, like 

 you, seem to remember a connected essay by Darwin on the mental 

 development of an infant ; but I forget where it appeared. Tiy 

 back volumes of Xature. He quotes observations on an infant of 

 his own, though, on pp. 151 to 153 of his " Expression of the 

 Emotions," &c. — Chas. Few. W. H. France. It is wholly needless 

 for you, and other correspondents, to continue to write that the 

 figure in letter 1490, p. 372, is a magic square. That is evident on 

 inspection. What a " Lover of Things Occult " wished to know — 

 as I understood — was the connection between the figures he gave 

 and the supernal powers attributed to them, and this nobody but 

 Mr. Mathias has attempted to touch. — Axoxtmous. The headless 

 chicken of your paragraph is obviously a " Great gooseberry," 

 from some American paper. — W. R. P. Tou must use your 

 own discretion. The fact of such a form of expression appearing 

 " in print " proves but little, indeed. What is to hinder a swimming- 

 master or a conjurer from dubbing himself "professor" ; the pro- 

 prietor of a middle-class day-school, held in one room, from calling 

 it a " college " ; or a man from advertising a common needle as 

 "a sewing-machine"? — J. Joxes. See Glazebrook's "Physical 

 Optics," published in Longmans' " Text-books of Science." — OxE 

 Who Waxts to Learx. " Whitaker's Almanack " is the best and 

 most trustworthy after the " Nautical," but, of course, it does not 

 contain the mass of information which the latter does. Tes; a 

 2^-inch telescope with a power of 180 ought to divide t' Lyroe, and 

 even theoretically t". — M. Weldox. The conductor of this journal 

 has nothing to add to his quoted expression of opinion. See 

 paragraph (in capital letters) with which the heading to the 

 Correspondence Column concludes. — W. TorxG. Received. Re- 

 gret my Inability to attend your conference. — Persifal M. 

 Yearsley. Is the story in any way authenticated ? or is it 

 merely a magazine novelette ? — Johx E. Chaster. The 

 Editor of this Journal does not buy back numbers with the 

 .advertisement sheets missing ! You must advertise them if you 

 want to get rid of them. Were any articles required on the subject 



you mention, they would, of course, be committed to Mr. Slingo. — 

 WiLLLAM Reid. Returned with thanks.— J. T. E. Thanks; but the 

 method you illustrate is " as old as the hills." Certainly, I was 

 familiar with it when I was fifteen. The figure looks more simple, 

 but, if you try for yourself, yon will find that the necessary calcula- 

 tions are certainly longer and more complicated. — J. DuxcAX. I 

 cannot engrave a figure here, but see Loomis's " Treatise on As- 

 tronomy" (not his "Practical Astronomy "), pp. 154 and 158 ; or 

 Brinkley's "Astronomy" (by Stubbs & Brvinnow), pp. 132 and 133, 

 though into the latter demonstration rudimentary trigonometr}- 

 enterg. — C. Roscoe's " Elementary Chemistry," published by Mac- 

 millan, and Ganot's " Physics," Longmans & Co. — W. Wroxg. I 

 really cannot afford the space merely to give the English names of 

 the letters of the Greek alphabet. See Cassell's " Elementary 

 Lessons in Greek." — Sharp <t Co. Delayed through being addressed 

 to the Editor, instead of to the Publishers. — A Casual Reader. 

 See answer to — well, to every initial in the alphabet — re letter 

 1490. — J. A. M. See Darwin on sexual selection iu his " Descent 

 of Man." — Nigel Doble. Put your eye-pieces 10 inches behind 

 the object glasses. There are two sorts of black colouring used in 

 optical instruments; the dead-black in the inside of eye-pieces, 

 tubes, and the like is made of lamp-black, mixed as thick as putty 

 with gold-size, then diluted with turpentine, and painted on with a 

 camel's-hair brush. Stages and outside brass work are generally 

 blackened with chloride of platinum, brushed on while they are 

 hot. — Starc h. The formation and evaporation of clouds is far from 

 being an uncommon phenomenon in daylight. It was seeing them 

 black upon the night sky which must have attracted your attention. 

 As to their shape, &c., see Vol. II. of Kxowledge pp. 278 and 32G. 

 — W. 6. World. No ; the focus of the object-glass falls between the 

 lenses of a Huyghenian eye-piece. A 6-inch objective should carry 

 powers from 20 (for comets and nebulce) to 600 (for very close 

 double stars only). I cannot recommend tradesmen. Read the 

 advertisement columns. — E. P. L. and X. Y. Z. both complain that 

 Mr. Clodd's papers trench, indefensibly, on purely theological 

 grounds. The difficulty of discussing the origin of primitive beliefs 

 — in fact, the origin of man himself — without offending theological 

 prejudices is doubtless very great. — A. Peaesox. Thome's " Struc- 

 tural and Physiological Botany " in Longmans' " Text-books of 

 Science," is excellent. I know nothing of what is demanded of the 

 advanced student in the wretched cram system at Brompton. 

 AxoxYMors (Ipswich). — Why do you not address the Chess Editor ? 



A ii>iART trick has, says the Athenmum, been played Mr. Max 

 O'Rell by a Yankee firm. Before the sheets of "John Bull's 

 Womankind," sent in advance of publication to America, could be 

 got into type, the work had been translated from an early copy of 

 the French original, and issued by a New York publisher. The 

 author's chance of any profit from the American sale of his book is, 

 therefore, destroyed. 



Christmas Presexts. — Doubtless for some very good reason, 

 Christmas-tide, now so rapidly approaching, has ever been associated 

 with the giving and receiving of presents. We do not propose, 

 however, to write a homily either in support of or against the 

 custom, though possibly a few adequate reasons from the latter 

 point of view would find favour in the eyes of Paterfamilias. 

 Knowing, however, how much thought is often wasted in selecting 

 suitable presents, frequently with unsatisfactory results, we venture 

 to offer to our readers a suggestion in this direction by again calling 

 attention to the unrivalled claims of photography as an attractive 

 and enduring amusement, not only for young folks, but, we make 

 bold to say, for all who may put it to the test. A day or so back we 

 had an opportunity of inspecting some of the newest sets of portable 

 photographic apparatus offered to the public by the London Stereo- 

 scopic Company, of 110, Regent-street, and we were struck by their 

 extreme suitability as presents. Sets completely fitted with all the 

 latest improvements devised for rendering photography a pleasure, 

 can be procured at prices to suit all pockets; the purchase of the 

 most expensive qualities, however, does not involve unreasonable 

 outlay. We may remind our readers, too, that buyers of the better 

 descriptions of apparatus are entitled to avail themselves of a 

 course of free lessons iu photography, given by competent in- 

 structors on the Company's premises in Regent-street. We 

 saw many desirable sets of apparatus during our visit to 

 the studio, but we can specially recommend to intending par- 

 chasers those known as the "Cychsts' J-plate," the "Company's 

 i-plate," and the " Company's whole-plate." These three sets are 

 of different prices, and manifestly of varying sizes ; but each is a 

 thoroughly reUable and complete apparatus which cannot fail to 

 please. 



