Sbpt. 26, 1884.] 



♦ KNOWLEDGE ♦ 



267 



I imagine there can be no doubt as to the meaning of what 

 1 have above suggested ; it only remains for those whose practical 

 acquaintance with such things, and whose theoretical powers of 

 insight are sufficiently recognised to pronounce on the prime ques- 

 f ion whether an archimedoan screw, revolving in air, could be made 

 largo enough and strong enough, and could be rotated with a 

 sufficient velocity, to produce the necessary lifting power. It will, 

 J think, bo admitted that the prima facie likelihood is considerable, 

 .cUhough something more than that is needed to stimulate experi- 

 ment. 



There is one point on which T must add a caution. The re- 

 .sistance of the air, due partly to friction and partly to the pitch of 

 the screw, must find some sufficient opposition in the machine itself, 

 otherwise the latter will turn in the contrary direction. This 



suggests a second fan, with a contrary pitch — or a subsidiary fan 

 'levoted solely to counteraction. The relative advantages of these, 

 and the disposition generally of the fans with respect to the car, 

 ure points into which I will not enter, further than to hazard the 

 opinion that the greatest economy would bo attained by two equal 

 screws of opposite pitch, revolving in opposite directions, and 

 having their axes in one straight line. 



The accompanying diagram, without pretending to be a design 

 I'or a flying machine, is intended to show how the difficulty glanced 

 ;Lt above, can be entirely met. Power is supposed applied either 

 I hrough the crank or by a coiled spring. If two or more screws 

 support a platform, there is no need for other counteraction than 

 theii'own. J. Heeschel. 



LETTERS RECEIVED AND SHORT ANSWERS. 



[Before these lines meet the reader's eye, I shall have left 

 England for a month's very sorely needed rest. Correspondents 

 must hence bear with me if the replies in this column are daring 

 that period practically confined to an acknowledment of the receipt 

 <if their communications.] — Dorothy Forstek. I know of nothing 

 ».'xactly answering your description ; but you might try Miss 

 Vonge's "Aunt Charlotte's Stories from Bible History," any of 

 the volumes of the " Line Upon Line " series, or even " Piunock's 

 First Steps to Bible and Gospel History." Ynu had better write 

 to Moffatt & Paige, Warwick-lane, London, on the subject of cheap 

 historical wall pictures. They are the likeliest people I know of 

 to publish such things — if, indeed, they are published. In connec- 



tion with the Kyrle Society, apply to Miss Hill, 14, Nottingham- 

 place, London, W. — W. G. 'The lines you quote are from a mediajval 

 drinking-song in Leonine Latin, and may be construed, " I mean to 

 die in a tavern ; expiring with the wine at my lips (as the English 

 singers say) May the Almighty be propitious to this sot." Truly, 

 nut a very edifying sentiment ! — L. A. W. Looking through an 

 astronomical telescope is not injurious to the sight, especially it 

 you can teach yourself to do it (as you soon may) with the other 

 eye open. Using the eyes alternately, too, ia good. Look in Map VII. 

 of " The Stars in their Seasons " for ? and »; Herculis. Draw an 

 imaginai-y line from t] to ^, and one-third of the way along it you will 

 find the cluster you refer to. The period of Encke's comet is not 

 5 but 3'3035 years. It was, I fancy, last seen by Tebbutt, in 

 August, 1878. Halley's comet will not return until 1911. Cer- 

 tainly Vesta, Juno, Ceres, and Pallas can be seen with a 2i-inch 

 object-glass ; Vesta sometimes even with the naked eye. They are 

 difficult to distinguish from fixed stars merely by their aspect. — 

 W. G. Wiseman, F.R.G.S., on opening a duck's egg the other 

 day, discovered, in addition to a perfect yolk, another small egg, 

 about the size of a pigeon's, with a hard shell. Will any 

 embryologlst explain this not very common phenomenon for his 

 benefit ? — CoPE WniTEHOt'sF. offers to furnish gratuitously to any 

 author or publisher cliches of his woodcuts of .StafEa printed in his 

 paper read before the geological section of the British Association 

 at Montreal. — B. O'Reilly. In the morning. A table-lamp, cer- 

 tainly. — Wave. From the friction of their lower parts against the 

 beach as they approach the land. There is no " easy " way of 

 working out moon-rise, which, in any accurate form, is a very com- 

 plicated piece of calculation. Of course, it must be computed 

 afi'e.«h for each locality. It is given for London in Whitaker's 

 Almanack, but the vol. for 1885 is not yet out. — F. L. Armitage. 

 See Lommel's " Optics and Light" in the International Scientific 

 Series. — T. R. C. sends me a prospectus of "The Society of 

 Science, Letters, and Art of London," which seems to give concerts, 

 conduct examinations, grant hoods, gowns, and decorations or 

 badges (or, I suppose, the right to wear them), furnish lecturers, 

 ic, for literary, musical, and scientific evenings, and require funds 

 to meet expenses. F.R.S.L. means Fellow of the Royal Society 

 of Literature. — A. S. Orr. " Five of Clubs" is, unfortunately, at 

 present on the other side of the Atlantic. — A. Roberts. In these 

 latitudes, jnst prior to the spring equinox, the inclination of the 

 ecliptic to the horizon is very considerable. Moreover, the moon's 

 orbit is inclined some 5° to the ecliptic, so that she may be 5° north 

 of that again, and the line joining her centre and that of the suu 

 seemingly nearly perpendicular to the horizon after sunset. Hence 

 the diameter passing through her cusps lies pretty nearly horizontal 

 when she is very young, and she seems to " lie ou her back " in the 

 western evening sky. The idea, however, that this is a cause or 

 sign of rain is as utterly baseless as that her so-called " changes" 

 affect the weather.— H. C. S. wants details and an explanation of 

 the Berkeley-square Ghost. I am unfamiliar with either myself. 

 Can any reader furnish the necessary particulars? — J. B. Findlay. 

 The information contained in every one of the astronomical works 

 advertised by the Messrs. Longmans, on p. viii. of the advertisement 

 sheets in Knowledge, for Sept. 19th, is brought up to the very latest 

 date. See, too. Ball's "Astronomy," by the same publishers. New- 

 comb's " Popular Astronomy," published by Macmillans, or Sir 

 Edmund Beckett's excellent "Astronomy without Mathematics," 

 issued by the S.P.C.K. The hypothesis that Alcyone is the centre 

 of the visible universe (a mere fancy of Miidler's, of which Sir John 

 Herschel at once pointed out the improbability) has been definitely 

 shown to be groundless by the study of the proper motions of the 

 stars in different regions of the heavens. The latest and most 

 trustworthy theories on the subject of variable stars are those of 

 Professor Pickering. See the " Universe of Stars," for the struc- 

 ture of the heavens. I think that Todhunter's books on Trigono- 

 metry are, perhaps, as good as any yon can get ; but Spherical Trigo- 

 nometry is not an easy subject to get up without a tntor. — A. J. 

 Harvey. I doubt if there is a single astronomical reader of 

 Knowledge who is ignorant of Schwabe's discovery of the perio- 

 dicity of sun-spots. His period, however, has since been shown to 

 be erroneous. — T. K. H. Received. No time to deal with your 

 charming little problem now. — Pso Liberis. See reply to " Anony- 

 mous" on p. 247. — E. L. T.iylor, S., K. H., S. B. Partridge, 

 G. D. Evans, F. ,S. Thompson, W., and many others who send 

 answers to the Figure Puzzle. Thanks ; but the two letters printed 

 contain at once a reply to and an explanation of the theory of the 

 question. — Colonel Herscuel. Tour interesting letter was, of 

 course, marked for insertion. Replies in this column are mainly 

 confined to correspondents whose letters are not intended to appear. 

 — Dr. E. Geoth. I failed to lay my hand upon the proof to which 

 1 referred, and am very much too busy at this instant to be able to 

 devote an hour or two to hunting it up. Meanwhile may I suggest 

 for vour considtration the millioTi? of venrs which it must, ex ne-.i- 



