loO 



KNOWJ_EDGE 



[Dec. 23, 1881. 



AN INSTRl'MKNT FOR DRAWING TTTF CONIC 

 SECTIONS. 



By TfioMAs TiioHp. 



rjlll E I'astriiment sho^vn in tlic nccompnnjing .ski;tch, Fig. 1, may 

 -L be nsed for ibtaining (igarca of the cniuO flections. It ia 

 Huito origimil with me, ami can be iiirulc Trithoat any orcnt 

 .lifficuUy. 



Fig. 1. 



The rod throngh the ball and socket joint at A should be as 

 enlarged at B, the edge in line with the scribing-point being exactly 

 central, as shown at C. 



The instnimeiit is sketched as describing a parabola, but is 

 equally suited for any other of the conic sections. Fui-ther details 

 if required. 



For describing ellipses, the instrument shown. Fig. 2, is extrcnuly 

 useful, and may not be known to many of your readers. 



OiR Next Ximber.— We have been «bliged to defer to next 

 week two illustrated articles, one by a "Fellow of the Royal Astro- 

 nomical Society," on Work with a Small Telescope; the other by 

 the Editor, on the Great Tyramid. in compliance with the wishes 

 of many readers, the star maps, which have hitherto appeared 

 weekly, will be combined into a single map (on the same scale), 

 which will appear in the first week of each month. In the other 

 weeks some subsidiary maps will be given, illustrating the motions 

 of the heavenly bodies during the month. There will also be 

 given each month a pajier dealing with star names, constellations, 

 figures, <tc.— [^Kd.J 



Errata. — The comet referred to in Mr. Denning's letter of last 

 week (letter 122, p. IK)), was not the one which bears his name 

 (comet /. 1881), but comet ';, 1881. The letter .7 was. misread. 



Ill llniilv to ;■>.•; n 1 U! Incf i;>,o I.„t ,i„., f. ... 1)..„„_ .'.„„.1 D„.„„. 



icttersf to tfje eiJitor. 



[The E'iifor doe» not hold himte{f retponnbU/or Ute opinions of hU correfponJnU. 

 B0 cannot undertake to return manuacr\pi$ or to corrftiond ycith their itriftrt. All 

 commnni/^atiotu thonlJ be a* $kort a* patnblt, consUttktiy tcith full and clear Halt' 

 menlM of the writer's nuaninff.} 



Aff Editorial eommuniciitiont should he addressed fo the Editor o/ K^owiMTtot ; 

 aH Jluinegs ccmmumcations to the Pullishers, at Ue ffjirf, 74, Great Queen- 

 street, H'.C. 



Alt Remittances, Cheques, and Fost'OJtce Orders should be made payahU to 

 Messrs. Wym.tn 4" Sons. 



•»• All letters to the FHtar riH be Xnmhered. For eome'iience of reference, 

 correspondenis, vhen r^errinff to any letter, kUI oblige by mentioning its number 

 and the ptige on which it appears. 



All Leff-.rs or Queriei to the Editor vhich reqnire attention in t^e current issue of 

 KVOXTLYHOH, should reach the Publishing Office not later than the Saturday preceding 

 the day qf publication. _^^__-. 



*' In knowledge, tbat roan only is to be contemned and despised irbo is not ia ft 



state of transition Nor is there anything more ftdrerse to accuncj 



iban fixitj of opinion." — Faraday. 



" There is no harm in mukin^ a mistake, hot preat harm in makiag none. Show 

 me a man who makes nu mistakes, and I wiU show yoa ft miia who b&a dona 

 nothing." — Liehig. ^_^™_ 



#111* CoiTfSpontitnrf Columns. 



PLANS FOR THE NEW YEAR.— DARWIN AND DESIRE.— 

 SPIRITUALISM. — PLANETS HIDING STABS. — VIBRA- 

 TIONS OF LIGHT IN ^ETHER.— VECTORS VESTIGES 

 OF CREATION.— NEWSPAPER SCIENCE.— THE (xEEAT 

 PYRAMID. 



[136J — With the iirst number of the year 1882 we shall some- 

 what modify onr plan, experience and the suggestions of many 

 correspondents having shown that some features which we have not 

 yet introduced wonld be desirable, and that others which we had 

 thouglit desirable are cither not so, or inconsistent with seme pre- 

 senting greater advantages. The task of selection is not altogether 

 easy. We have been reminded much of the old man with bis 

 donkey and two sons in the fable, whose fate, it will be remembered, 

 when he tried to please every one, was to be thrown into the river, 

 along with his three companions. We are urged — (I) to widen our 

 space for correspondence ; (2) to keep out correspondence ; (3) to 

 encourage paradoxei-s t o disport themselves in our pages; (4) to 

 silence them utterly ; (5) to explain simply the principles of every 

 science on the face of the earth, all at the same time ; (0) to 

 leave all such explanations to text books ; (7) to increase 

 our size ; (8) by no means to do so ; (9) to publish all the 

 four maps for the month at the beginning of each month; 

 (10) to publish them ♦.eekly, as we do, but with a page or 

 two of explanation, ic. ; (11) to have the stars punched out of 

 the paper; (12) to have the names of all the stars; (13) to have as 

 little writing on the maps as possible ; (14) to leave out the small 

 stars; (15) to letter them as well as the others; (16) to give also 

 weekly zodiacal maps, with paths of planets, moon, comets, &c. ; 

 (17) to announce all astronomical phenomena; (18) to remember 

 that the almanacs do that for us; (19) to h.iT0 more astronomy; 

 (20) to have less astronomy ; (21) to be rather less simple ; (22) to 

 be more simple ; (23) to give reports of societies ; (21) to give 

 digests of reports; (25) to give no reports at all ; (26) to announce 

 meetings of societies; (27) to devote space to no such purpose; 

 (28) to limit the mathematical column to the discussion of really 

 difficult problems; (20) to use it to explain matters for beginners; 

 (30) to omit it altogether; (31) to extend the whist and chess 

 coluinns; (32) to sliortcn them; (33) to leave thoin out; (34) to 

 have exchange columns, sixpenny sale columns, Ac. ; (35) to have 

 none of these ; (36) to offer prizes, have essay columns for girls 

 and boys, A'C. ; (37) to eschew such allurements ; (38) to have longT 

 articles ; (30) to let no article exceed a page, and few be longer 

 than a column; (40) to have articles on ancient philosophy, modem 

 scientific biographies, ait and the drama, puzzles, enigmas, hints for 

 collectors of shells, medals, seaweed, Ac, Ac, Ac, ad infinitum. To 

 .•ill which, all that wo can reply is that we will do our best to please 

 the greatest number. 



iir. Newton Crosland, accusing me of verbal shuflling, claims 

 from me an apology. Darwin, he says, does speak of the "endea- 

 vour," though not of the " desire," of the rattlesnake to frighten 

 aw»v its enemies ; and the two mean the same. Truly they differ 

 i;,.i« . u..* ...1...* Ar^ /^«..r.!«,..4 c^',A ...n.. ♦!..,» " nn.-.-;.. nt«,.;KiitAH th** 



