April 21, 1882.] 



• KNOWLEDGE 



539 



ansftunsf to CoirfSponUfiitei. 



*^*All eommunicationt for the Editor requiring early attention ehould reach the 

 Offlce oti or b^ore the Saturday preceding the current ieeue of Kkowledob, the 

 tHcreaeing circulation o/ychich compels us to go to prett early in the week. 



HlXT3 TO CoEBBSPONDBSTS. — 1. ifo queitions aeting for scientijtc injormation 

 lan be aiitmrred through the poet. 3. Lett ere tent to the Editor for corrcipondenti 

 tannot be forvarded ; nor can the names or addrettes nf correspondents be given in 

 answer to private inquiries. 3. Correspondents should vrite on one side only of 

 the paper, and put drawings on a separate leaj. 4. Each letter should have a title, 

 and in replying to a letter, r^erence should be uade to its number^ the page on 

 wkiek it appears^ and its title, 



[In response to the wishes of a large number of correspondents, 

 answers to questions which /icreo/fcrmay reach us will not be given 

 luiJer this heading. Wc have had to discontinue Queries and 

 uiplies because, wliile taking up much space, they only interested 

 I few. The answers under the present heading were open to the 

 iame objection, and to the fiu-ther one that they were mostly unin- 

 telligible to all save the individual querists. As we had to find 

 room somewhere in response to the growing demands npon our 

 -pace, wo have decided to find room in these sections, in which 

 Illy the few take interest. Questions which hereafter may reach 

 .^ will be acknowledged and forwarded to tliose who write for us 

 upon tlic subjects to which such questions relate ; and should those 

 writers see fit, may suggest articles, or paragraphs for articles, of 

 interest, we trust, to all |our readers. Hereafter, Knowledge will 

 occupy the same position in this respect as the Athenwum, Academy, 

 and Nature, in which there are no columns for queries or replies, 

 and very few answers to correspondents. Questions which, being 

 suitable in themselves, come in suitable form, will appear under 

 head " Letters to the Editor," and may be answered under the 

 same heading. — Ed.] 



MISCELLANEOUS. 

 E. D. G. Yes ; Ladder of St. Augustine appeared in 1858. 

 Why did you not remember this beifore ? — G. E. Wynne. If 

 only we could have 100pp., such letters would be useful. But 

 what can we possibly do with 2 ft. x 1 ft. MSS. ? — H. G. A. W. 

 East wind is not cold in summer, or in all countries. — 

 J. A. Ollard. Many thanks for kind suggestions ; will con- 

 sider them, and attend to other matters later. — Robert Mac- 

 PHERSON. The subject of legal responsibility in cases of mental 

 disturbance is full of interest. I shall not overlook the suggestion. 

 Has the enunciation of rules about "shall" and "will" ever 

 made any difference as to the use of these words ? Macaulay remarks, 

 in his essay on " Lord Bacon," that though " not one Londoner in 

 ten thousand can lay down the rules for the proper use of will and 

 tholl, not one Londoner in a million ever misplaces his tuill and 

 thall ;" and that though "Doctor Eobertson could undoubtedly 

 have written a luminous dissertation on the use of these words ; 

 lie sometimes misplaces them ludicrously, eveu in his latest works." 

 — Desespoir. We cannot in any way be responsible for the bona 

 fides of advertisers in Knowledge. — E. Rowe. No ; we regret much 

 more than you can such stupidity on the part of some booksellers. — 

 W. H. JoNKs. I do not think that Professor TjTndall, or any other 

 student of science, doubts that in past times, under particular con- 

 ditions, there may have been spontaneous genei'ation. He only 

 asserts that under any conditions, now, which exclude living 

 germs, no spontaneous generation occurs. — C. J. Brow.v. Tour 

 letter rendered almost illegible by blurring. We, too, were 

 disappointed that no direct remedy from bad fires and venti- 

 lation was given, short of rebuilding all our houses. On the spoil- 

 bank matter, Mr. Williams did not mean, we think, that sponta- 

 neous generation was always the cause, but only that it was a 

 common cause. — S. M. SUTTON. So far as a mere outsider can 

 judge, the " inner voice (so termed) " utters nonsense ; perhaps 

 others may find a meaning in "the combatieal force of pseudo 

 metallurgy." — A. Yes; but violet is not blue with red in it. Have 

 yon ever seen the violet of a pure spectrum ? — R. J. Houlton. Thanks 

 for replies. Dog anecdote resembles others with which our readers 

 are familiar. — Jones <t Barber. Thanks for invitation. — Phil.\- 

 LETHEs. Egyptologists agree, nem. con., in the earlier dates, 

 and have not overlooked the point to which you call attention. 

 Osbum's views are now entirely out of date. Can you name a 

 living Egyptologist of any standing who maintains that the com- 

 mencement of the -Ith Dynasty could not have been earlier than 

 2200 B.C. — .Alexander Howell. It is verj' good of you to correct 

 Sir Edmund Beckett about the law of patents ; but for our own 

 part we should as soon think of explaining to Mr. Muybridge the 

 elementary principles of photography. — A. M. Smith. Without direct 

 evidence, such theories are of little value ; to the question " May 

 not so and bo bo such and such ? " the answer is either " It may be 

 so," or " It may not be so," neither of which advances us much. — 



W. F. S. May we not express our thanks for your kind and en- 

 couraging words ? — iRLs wishes to learn where a prism such as Mr. 

 Higgins describes at p. 470, No. 22, and mounted as described, 

 can be obtained. — A. W. W. W. W. Thanks, but explanation rather 

 doubtful. 



ASTRONOMICAL AND MATHEMATICAL. 



M. H. C. Ought we not rather to say that Sir E. Beckett rejects 

 the theory which you show to be incorrect, and that the centri- 

 fugal theory as modified (but not as it has been propounded by 

 several) is correct enough ? This, however, applies rather to the 

 correction of the centrifugal force than to his omission of moon's 

 total attraction. But it is difficult to say what have been the exact 

 ideas of some who have propounded a centrifugal theory of the 

 tides. — Cantab. You do not consider the earth's more rapid 

 motion in perihelion at time when her orbit was at its greatest 

 eccentricity. The influence of a short, very warm summer would 

 not counteract the influence of a long, very cold winter. — H. C. W. 

 Does not that amount to what wo have already said about the log. 

 paradox ? — H. B. L. Clifford and Helmholtz have not merely main- 

 tained that material space is or may be limited, but that abstract 

 space may be. The former question would be purely speculative ; 

 the latter would be admissible if wo could admit that the twelfth 

 axiom of Euclid is incorrect. Although the question you discuss 

 belongs to natural, not to dogmatic religion, it is scarcely suitable 

 for discussion here. — S. M. B. G. We thought the papers too 

 diffuse, and the subject-matter too familiar. But furtlier, you 

 selected a subject in relation to which we have exercised some self- 

 denial already, in admitting papers from others which we might 

 very well have written ourselves. We can only give a certain 

 portion of our space to that subject, and we want to leave a little 

 of that space to ourselves. We cannot answer bj' letter. — Air. 

 This is scarcely the place for aerial tricycle. — J. P. H. Try 

 your method in case of a rectangle fifty times as long as 

 it is broad, and show how two cuts suflice in that case. — 

 G. F. Ogilvy. Precisely the same, whether centre of motion is out- 

 side or inside the body so moving. — A. T. Skinner. Y'our solution 

 of Mogul's problem correct. — F. H. S. The subject is closely 

 related, as you say, to inquiries into nature of space and time ; in 

 time we hope to find space for it. — Vigilans. My Library Star 

 Atlas would be of more use for telescopic work than either of the 

 series of maps (by me) you name. — J. W. C. The transmission of 

 such wave motion is akin to what we see on the surface of water, 

 where the motion of the particles is (in the main) at right angles to 

 the direction of transmission. — HfGii Coleman Davidson. The 

 earth's poles describe two small circles, as you suppose. — G. L. H. 

 Each ray from the disc of a planet is disturbed, just as the rays 

 from a star ; but as the disc of a planet is not appreciably a point, 

 as a star is, and the different rays from different points of the disc 

 are differently disturbed, the disturbances in some directions 

 counterbalance those in other directions, and we have a steady 

 light. — M. L. Rouse. Y'es, the paradox is as you describe it. — J. B. 

 Shipley. One can only consider a lever as intended to move 

 something. The P and W of the account of any lever can always 

 be interchanged ; and you can also, if you will, interchange E, the 

 resistance at fulcrum, with W. In inquiring into propulsive force on 

 boat, we must regard the boat with its load as the weight, the 

 energy exerted by the rowers as the power. It m.ay be very absurd, 

 but we cannot help ourselves. — G. Rimington. — Thanks, but reply 

 about Sinking Funds rather longer than the general interest taken in 

 subject justifies. — Comets. Alas ! your theory will not do. It is hope- 

 lessly remote from possibility. The term " paraboloid," by the way, 

 is already in use, not for your mixed curve, but for a surface. — 

 John Hamer. You could get clearer ideas of the moon's rotation 

 if you studied a trustworthy treatise on dynamics, than by waiting 

 for ideas " in the watches of the night." The idea of the moon not 

 rotating on its polar axis, but on the equatorial axis ! Define polar 

 axi.=, and see what comes of your idea. — Jas. Offord. Received, 

 and will be used. Do you wish Zodiac of Dcnderah to be engraved ? 

 — W. Edwards. An annular eclipse of the sun -observed in this 

 country on Sunday, May 15, 1836. — Jas, Deas. You have not either 

 statement quite right. The earlier (in my essay. Gamut of Light) 

 was erroneous. The determination of stellar motions of approach and 

 recession too difficult for anything like exactness to be obtained. 



Stttfrs iRffcibrt. 



Alex. Howell, Onward, A Novice, Z. 0. Z., Montpellier, A. Fisher. 

 W. G. Williams, Mary Powell, J. F. Humphrey, W. P. B., Crcssbar 

 (questions vague, or already answered, or otherwise unsuitable). C. 

 Carter, W. J. Hamsmith, A. J. Dohcrty, J. Pepperson, W. G. 

 Williams, Nag's Head (Nac/'s Head ? Are you sine ?), Emily F., J. 

 Harvey, M. Murgetson. 



