JtsE 16, 1882. 



♦ KNOWLEDGE <> 



45 



a given star, whose E. A. is knowii, will transit the meridian at any 

 given time. For instance : — 



Keqnired to know en what dav Arcturus will cross the meridian 

 at three o'clock. 



h. m 



Arcturus, E. A 1110 



Spin. a 



Then to the constant 3 22 



Add 17 h. divided by 2 8 



70 m. „ 4 17 



12 9 



which is the 9th day of the 12th month, or Dec. 9tli. 



In the X. A. the sid. time at noon on Dec. 9th is 17h. 12n; 



Snetorrs to Coiitspontmits. 



the Editor req 

 Office on or before the S'.tturJutf precedivg 1 

 inereating eireulaiion of which compelt u» to g 

 HI5T3 TO COBBBSPO:fDByTS. — 1. A'o qhe>t 

 can U anncered through the poet. 2. Leferi 

 cannot he forvtirded ; 





eittion ihotdtd reach the 

 of KSOWLEDSI, the 

 ■ preee early in the week, 

 t atleing for eeientijic information 

 it to the Editor for corrttpondentt 

 <lf correirpondentt t 



private inguiriee. 3. Correspondent* ehould write on one tide onlf/ of 

 the paper, and put drawing* on a eeparate leaj. 4. Each Utter ahotild hace a title, 

 and in rephfing to a letter, r^erence ehould be mide to iU number, the page on 

 vkick it appear*, and iU title, 



Jko. T. Seccomee. I fear it would be difficult to prove that 

 diamonds are condensed comets. — E. 11. B. Stephensox. The 

 objection to Tyndall's explanation of sound heard in shell, as a case 

 of mere resonance, is that a much larger and more perfect sonnd- 

 gatherer, applied more suitably to aid the hearing, does not produce 

 the same degree or kind of noise ; as regards pressure of the shell 

 against the ear, the sound is heard when the shell does not touch 

 the ear. — W. Benson. The idea has been suggested before that a 

 comet's tail is an electrical phenomenon. As presented by you, the 

 theory is open to the objection that in the case of a retreating 

 comet the tail occup'es tl\e part of space towards which the comet 

 is moving. — G. W. 1 think you have misunderstood the object 

 of the articles on " Science at the Eoyal Academy." Their author 

 is discussing the effect of 'luasi scienti6c errors on the artistic 

 qualities of pictures and sculptures. Truth is as essential in art as 

 in science. It so chances that being at the Eoyal Academy a day 

 or two since, I h.eard two ladies, who certainly had not read 

 Knowledge, remarking on the odd- looking wrists in " Day Dreams." 

 Anatomy recognises as the cause of that odd look, an incorrectly 

 drawn or else malformed carpal bone. You consider his criticisms 

 «honld first be applied to the illustrations in scientific works. 

 Where errors in these escape the eye of a scientific author, or where 

 there is a want of artistic ability in those employed to illustrate 

 such works, the defect is a matter to be regretted. But two wrongs 

 do not make a right. You say *' before we sit in judgment as to 

 the scientific correctness of art, let us try to improve the want of 

 artistic correctness perpetuated on behalf of science." Why should 

 not the other come first, especially just now when the Academy is 

 open. Thanks, however, for your suggestive letter, which should 

 appear in full if there were space. — F. Yelwoc. The cnly one of your 

 long string of questions which comes fairly within our fcopo 

 is the one relating to cycloidal geometry, and we can only say 

 that the subject is difficult, and not particularly useful, except 

 to mathematicians, to whom it is very interesting. You really 

 are unreasonable in asking so many questions. — Jas. Disney. 

 The instrument you name is an excellent one. — W. UiDi). We hope 

 shortly to give a short article on the new crater. — W. Coiidwei.l. 

 Wcare now publishing papers on Botany, such us you describe, under 

 the able superintendence of Mr. (irant Allen. — T. II. CovK says 

 publishers of J. E. Young's " Solution of Cubic and Biqnadratic 

 Equations" are Souter A Ijiw, Flcot-street.-TvB.tXAKi. The ex- 

 periment you explain can ])rove nothing. The green you get is 

 ! the green of an impure spectrum — G. C. D. M. Your questions 



I cannot possibly be arswcred, except in set articles, and 



jnst now we have not space for articles on gravitation. 

 I When and where did wo ever say that the moon's axis 



points earthwards? — If. Lancastbu. Thanks for picture of C'omto 

 Wells; but as it presents no features of interest, wo must 

 wait until larger views aro to hand. — S.\tei.i.itk. Your description 

 of the lunar phenomena insufficient. If it was around the moou, 

 it was not a bow. — L. Lucas. Have not space for your pajwrs la 



Cats and Dogs and Climbing Perches. — A. 11. Tou are quite right, 

 we dropped the 10 accidentally in the closing calculation, p. 585. It 

 does not greatly affect the result, bnt, as you say, r--4717, or is 

 rather less, not rather more, than i (per cent.). Thanks. — W. B. 

 Thanks for your kindly letter ; such letters do us good. We were 

 beginning to think ourselves quite ogreish where we had meant to 

 lie good-natured.— W. II. Fassett. Fifty or sixty it should 

 hava been. See answer to W. Southall below.— J. M. Cka^.v. 

 You would find very interesting information on the subject 

 you mention in Dr. C'ariwntcr's " Mental Physiolog)-." — E. M. O. 

 Thanks, but no space. — J. A. Miles. Many thanks for your capital 

 sonnets, but we am obliged to make it a rule to have no poetry in 

 Knowlepge, lest we should offend many whose poetry we shoald be 

 compelled to return. — J. Greenfield. We cannot well find room 

 for your speculations, which are, after all, rather vague. We may 

 note^that Legrange never asserted, still less proved, that the universe 

 was made to last forever; nor is there anything to show that the 

 solar rays can possibly work in circles. With regard to your other 

 suggestion, we must ask you, on the score of great pressure on our 

 time, to excuse us.— W.Soi'THALL. Seereply to W. U. Fassett, above. 

 Four square feet would be more than the average required for each 

 person. One square foot (or say IG x 9 in.) would do, remembering how 

 many children and infants there would be. — ZiA. The statement 

 that" the deviation of projectile is always to the right in both 

 hemispheres, apart from any effect due to the rifling, must be a mis- 

 print. Whether you are in the northern hemisphere firing a ball 

 due north, or in the southern hemisphere tiring a ball due south, 

 the ball comes from a place where the easterly motion is greater to 

 a place where the easterly motion is less, consequently it falls to 

 the east, which is to the right in the northern, and to the left in 

 the southern hemisphere.— H. Kyd. The Greek name of Meremy 

 was o ffr.X/3cuv, "the sparkling one."— W. Foley, M.D. We have 

 forwarded your communication to the publishers, which is, unfortu- 

 nately all we can do in the matter.— F.C.S. We regret very 

 much that your letter in answer to "Fabmeb" is altogether too 

 long for insertion. We feel bound in justice to give you an oppor- 

 portunity for rejily, but not for so long a reply as you have sent. 

 — J. BoBEBT.s. I'think I answered your question about Oliver 

 Cromwell, saving that I did not know about his a-strological ideas. 

 lias Alhaguc' means the "serpent-charmers' head," it is the bright 

 star in the head of Ophiuchus ; Has Algethi is the star in the head 

 of Hercules, the name means the " Kncelcr's head.— J. A. L. 

 RoBSON. According to every theory of the radiometer, tho 

 forces causing rotation are very slight. When air is present 

 these forces are quite unable to generate rotation against tho 

 atmospheric resistance.— Sobwon. Thanks, but our engraver can 

 make nothing of your picture, and without it your description is 

 difficult to understand.— W. Hoigiiton. Your letter U rather too 

 technical for our readers.— J. Wiiitelad. Your theorj" that new- 

 stars mav be explained by the solar system drawing nearer to them 

 at times,' will not bear analysis. The apparent fixity of a star in 

 position proves that the sun has not jnst drawn nearer to or farther 

 from that star.— F. W. Ckos-s. No planet or satellite has ever 

 been appreciiibly disturbed in its course by a comet's attraction. 

 Still, it would' bo unsafe to infer that a comets mass 

 is itself inappreciable. We know that comets aro followed by 

 many millions of millions of meteoric bodies, and those have 

 mass — C. A. Biston. The spots had not moved on the sun's disc 

 as thev seemed to have done, but the sun's disc had shifted in jxrai- 

 tion ; "that which had been its lowest point at tho first observation 

 was fnr to tho left of tho lowest point at tho second observa- 

 tion.— J. T. S. S. L.— The ball let fall from tho mouth of the 

 gun will reach the ground somewhat so<mcr than the one 

 fired horizontally from the fanu> height. The difforenco, bow- 

 over, would be verj- slight. It is due to the curvature of the earth : 

 possibly in practice a further slight diffennce may be caused by the 

 difference in tho atmospheric resistances.— O. It. Mvnne. 'Very 

 likelv that is the way in which tho "cold snap" arises; but until it 

 is explained, it can hartlly bo considered an explanation.- U. F. 

 I am not awaro that tho late eclipse has taught us anything new 

 in regard to metals in other worlds. Wo have not only known 

 that there are metals in tho sun, but even that our fcmiliar 

 metals exist iu stars so far away that their light takes years 

 in reaching us.— E. S. STANt»N. What you saw was a range 

 of lunar mountains, tho tops of which had jnst come into 

 sunlight. — W. iloBOAN. You have certainly a.lopted the best 

 of tho three courses which were open to jou. It wi.uld have 

 pained mo very much to have hianl that a r.a.:.r had to stand 

 on his head to read one of Ilho weather cl.nrts. and wo do 

 not want Knowleii-.k turned upside down. The fact is that " "y^J'K 

 to circumstances over which none of us had any control, the 

 engraver was verv much hurried in preparing the weather charts; 

 and in fixing th-. diagram for photograp' io -oiuct'on, he, unluckily, 

 plnc.-d one upside down ; fortunately thoso diagrams were simf.ly 



