012 



* KNOWLEDGE ♦ 



[May 19, 1882. 



All otlicr thinf^s boing ccpml, it may be tnken ns Fottlod that the 

 jicrcoiitnjjo of discnso in the iinmnnnred plots will bo the smullest, 

 or nearly so. 



" K.C.S." pivps no proof of his assertion that "good peat is 

 rcpial to stable manure." 1 again say it is nonsense, and wonder 

 anyone signing liimself " F.C.S." should have uttered it. 



This discussion was commenced in K.vowi.KDciK, and unless the 

 Kditor objects, another paper is not rc(|uired to linish it, but if 

 " F.C.S." has been a regular reader of tlie yield in past years, he 

 must have seen many of my contributions on the same subject, but 

 with a different signature. 



Would " K. \V. P." advocate an excess of mineral manure so as 

 to increase (he starch in potatoes, and does ho know if such an 

 c-Tcess would also increase the starch in the cereals i* Fakmeu. 



AN AKTIFICIAL MOOX. 



[406] — The moon question having been somewhat prominent in 

 your columns lately, a trial of the following experiment may prove 

 interesting to some of your readers. I venture no opinion as to 

 the connection in cause of the strongly-marked resemblance between 

 the real moon and the artificial. 



Take a soup plate, and slightly grease the surface with lard or 

 oil ; distribute irregularly in varying thicknesses about a table- 

 spoonful of su-called granulated citrate of magnesia. Take a basin, 

 pour in encnigh water to fill the soup plate ; shake into the water 

 about two-thirds the quantity of fine freshly-burnt plaster of Paris, 

 which will sink at once ; pour off nearly all the superfluous water ; 

 stir two or three times with a stick or spoon, so as to mix irregu- 

 larly the paste ; then pour it on the powder in the soup plate. The 

 water in the plaster will cause an immediate disengagement of 

 carbonic acid gas, which will rise in bubbles of various sizes 

 through it in irregular patches : the plaster almost immediately 

 setting, the shape of the outline of the bubbles and the walls of 

 i/hem become fixed, and, as a result, a most startling resemblance 

 to the eratered surface of the moon is produced. 



If a ])hotograph of this be taken with a strong light, the resem- 

 blance becomes so perfect as to deceive almost all who are not 

 professional astronomers. I believe that a little sugar, or syrup, or 

 gum in the water would produce larger craters, but I have not 

 tried this. A. Stewart Harbison. 



[As we have for several years used illustrations of the moon's 

 surface formed by Jlr. Harrison in the way described above, we 

 can vouch for the accuracy of his statements. — Ed.] 



" THE STARS AND THE E.ARTH." 



[407] — In your notice of the new edition of " The Stars and the 

 Earth," you remark that the author is unknown. Many years since, 

 two papers " On Good and Evil " appeared in ^[acmillan's Mar/azine. 

 The editor stated that those papers were by the author of " The 

 Stars and the Earth," Dr. Felix Eberty, of the University of 

 Breslau. In the Catalogue of the British Museum, both the English 

 and German edition of the book are under Dr. Eberty's name, and 

 as the two papers in itacmillan display the same ability as is 

 manifested in the book, the common authorship mav bo regarded as 

 certain. " J. \V. F. 



SIDEREAL TIME. 



[408] — The following neat method of ascertaining (without an 

 cphemeris) the approximate sidereal time at noon for any day of 

 the year, may be useful to such of the readers of Knowledge as 

 observe in the day time and have no rule of thumb way of finding 

 sidereal time. It was communicated to nie by Alfred Fryer, 

 Esq., of Elm Hirst, Wilmslow, with whom, 1 believe, it was quite 

 original. 



From the month and day increased by twelve months when 

 necessary substract three months twenty -two (lays, call each month 

 of difference two hours, and each day four minutes. Thus for the 

 day of issue of Knowledge, May 5 — 



5 months 5 days — 3 months 22 days = 2h. .'■>2m. sid. time. 



Nautical Almanac shows 2h D.31m. 



Ocean. 



The First Volume of Knowlkdge will be published early in June 

 next, bound in red cloth, gilt lettered. Price lOs. 6d. Vol. I. will 

 comprise the mmibors from the commen<rement (Nov. i, 1881) to 

 No. .10 (May 20, l)-82). As there is only a limited number of 

 copies, the Publishers advise that orders should be sent in without 

 delay, to prevent disappointment. 



Binding Cases for Volume I. will .also be supplied, price Is. 6d. 

 each. Complete copies bound (including case) for 2s. 6d. each. 



anstofrg to CoirrEfpoirtirntiSf. 



Otflr.c 



tiimralioiu for Iht EJilor rtgitinru/ rarly aHnlion ihould rmek Ih* 

 •fur^ thf Salurdity prfefting tht rurreni uiue of KltOWUlbOB, ti9 

 tncriannti cirrnl<ition of Khich compels ui fo qo to prtia «arly in thf vfek. 



UrNTS TO CoRBKKPONnRrfTS. — 1. iV*o qvrttionr atking for fritnt\jic information 

 can bf annwrred through the pout. 2. Lttlfrt tent to the Editor for correipondtnU 

 eannnt be forvnrded ; nor can the yiamei or uddrei»eii of correipondenit he fietn in 

 aneieer to prirale inquiriei. 3, CorrerpOHdeiitt fhould vrile on one tide only of 

 the paper, and put drattingi on a eeparate leaf. 4. Each letter ehould have a title, 

 and in replying to a letter, reference ehoutd be m^de to Ut number, the page tm 

 which it appears, and itt title. 



PniNEAs FooG. Rat her too many qjeries, now that the query 

 column has fallen. There will be 30 numbers in Vol. I., and as 

 many in Vol. II., after which the volumes will each contain 26 

 numbers — two volumes to each year. This has been arranged in 

 response to the request of several correspondents, that the first 

 numbers of volumes should fall, hereafter, in first weeks of January 

 and .luly. "Is Mr. Grant Allen a follower of Darwin?" Why, 

 certainly, — being a man of science. The east wind is supposed to 

 affect the health and spirits, because too dry ; I cannot say I 

 am satisfied with the reason, but the effect of the east wind is, 

 unfortunatelj-, not doubtful. — 0. H. Wingfield. That my 

 little joke about Mr. Proctor should have been misunder- 

 stood was fortunately of no moment ; but the lesson is worth 

 noting, as a misunderstood joke may be mischievous. I will 

 veiuure to say not one -American out of ten thousand would have 

 misunderstood me. — H. C. Astronomers know nothing of the 

 inclination of the asteroids' poles. Noise heard when shell is put 

 close to the ear is generally supposed to be due to the warmth of 

 the face, and consequent air currents. The explanation is doubtful. 

 Other questions answered in elementary treatises. — H. Brain. There 

 is every reason for believing that no former nations possessed any- 

 thing resembling our modern knowledge of mathematics. The 

 history of the progress of mathematics would fill many volumes 

 of Knowledge.— J. F. G. Persons who have been bom blind 

 and afterwards received sight have been found to require several 

 week;' experience, touching and feeling objects near them, and 

 so forth, Ot." "Tp they acquire the power of distinguishing the relative, 

 sizes and distances of objects. — Zion. Do not know of any such 

 collection. — W. H. M. There is not any difference between tossiag 

 a million coins at once, and tossing the same coin a million times 

 running, so far as the antecedent probability of the relative number 

 of heads and tails is concerned; but, of course, in tossing the same 

 coin a million times running, the observed result of the earlier 

 tossings modifies the expectation as tfi the final result. A portion 

 of th-at which had been doubtful lias liecome certain. You say 

 that at the start, in tossing a coin 100 times, it is likely there 

 will be 50 heads and 50 tails. On the contrary, this exact 

 equality is unlikely. Again, you say if the first toss is head, 

 it is 50 to 49 that the next toss will be tail. On the 

 contrary, the next toss is as likely to be head as to 

 be tail. The mathematical chance for the result of many 

 trials is considered in this week's Knowledge. — V. Wheeler. 

 Yes ; but with similar requests for weekly instalments of ten or 

 twelve different subjects, what are we to do ? — Stella. No one 

 else appears to have seen the two large red spots which remained 

 visible to you from 10.5 to 10.15 p.m. near Alpha and Beta, Ursa? 

 Majoris, on the 24th inst. Are von sure there was no optical illu- 

 sion ? Were your eyes tired ? or had you been looking at two dark 

 green masses ? — J. A. O. In treating of special subjects, writers 

 can name the books which they recommend. Letters asking for 

 the names of books on particular subjects should be sent to writers 

 who treat of those subjects. Science knows nothing about the colour 

 of Adam. — H. J. Iversen. (1) When a carriage is turning round 

 a corner, the inside wheel tends to rise off the ground, because 

 the body of the carriage has a centrifugal tendency outwanls 

 from the centre round which for a moment the carriage is 

 turning. (2) In railroads, the outer rail at curves is raised so that 

 this centrifugal tendency may be overcome by the tendency of 

 the carriage to loan over towards tlie side on which the lines are 

 lowest. (3) A turning carriage raises the inside wheel off the 

 grouud when the velocity is such that the moment of centrifugal 

 tendency exceeds the moment of the carriage's weight around the 

 lowest point of outer wheel. Thus, suppose M the mass of 

 the carriage, ?i the height of the centre of gravity above the 

 ground, r the velocity with which it is travelling (in feet per 

 second), d the distance between the wheels, R the radius of 

 the circle in which the centre of gravity of the carriage 

 is moving. Then the moment of the weight round the outer rail 



or lowest point of outer wheel, is t-2_, the centrifugal ten- 



