REVIEWS. 



AERONAUTICS. 



Aeroplanes in Gusts — Soaring Flight — and the Stability 



of Aeroplanes.— By S. L. Walkden. 184 pages. 4 folding 



plates. 8i-in. X6-in. 



(E. & F. N. Spon. Price 7/6.) 



We have heard and read much about the stability of 

 aeroplanes, some that is good and much that is bad ; but in 

 almost all cases the stability considered is that of the 

 aeroplane in calm air, a condition in which it does not much 

 matter whether the aeroplane is stable or not, so long as the 

 control is easy. 



Furthermore, the cases considered are those of machines in 

 which the surfaces bear definite inclinations to one another, 

 and retain definite shapes: that is, the whole machine is rigid ; 

 but Mr. Walkden opens up a far wider field with countless 

 possibilities, by considering the case of the non-rigid machine 

 which has a certain amount of elasticity introduced into its 

 construction. 



The author breaks fresh ground in the very first page and 

 continues to do so throughout the book. To start with, a 

 gust is defined and it is shewn that the proper and scientific 

 measure of a gust is " the acceleration of headway " impressed 

 upon the flying machine, the word " headway " being used in 

 place of the cumbersome but more general expression 

 "velocity relative to the air." The use of this as the 

 measure gives us a well-ordered explanation of all the 

 questions connected with stability, stresses, and soaring 

 flight in disturbed air. 



Throughout the book, pretty graphical methods are adopted 

 for displaying the author's arguments and results. Following 

 on a very complete analysis of gust effects, comes a fascinating 

 treatment of the problem of Soaring Flight. Many a reader 

 will look upon " ascending currents " as the only possible 

 explanation of soaring flight, but Mr. Walkden clearly 

 demonstrates that there are many other and commoner 

 conditions of the atmosphere capable of being utilised by a 

 bird, if not at some future date by a machine. For this 

 purpose, for example, what the author terms " Wheeling 

 Soaring " can be effected by making use of horizontal gusts, 

 or even of large horizontal whirls. That such gusts do always 

 exist and that Mr. Walkden's figures are quite ordinary, will be 

 recognised by anyone who has watched the motions of an 

 up-to-date wind-velocity recorder, which will shew that in 

 any wind there is, say, twenty or thirty times a minute, a 

 variation of perhaps from twenty per cent, to fifty per cent, on 

 either side of the mean. 



This may serve to shew the new and instructive matter that 

 is to be found in Mr. Walkden's book. The whole arrange- 

 ment of the book is of the same high quality as the contents ; 

 it is well printed, with a very complete index, and the plates 

 are arranged so that they can be studied while reading without 

 turning back the pages. We congratulate Mr. Walkden on 

 this addition to science. -f yy K. C 



ASTRONOMY, 



Astronomy.— By G. F. Chambers, F.R.A.S. 335 pages. 



350 illustrations. 8 coloured plates. 6iX4£-in. 



(Hutchinson & Co. Price 5/-.) 



Mr. Chambers is very well known as a writer of astronomical 



handbooks. The present work is intended for " the man in 



the street" who desires a speaking acquaintance with the 



subject, without going into any abstruse questions. In one 



respect the book may be unreservedly commended, viz., its 



illustrations, which are excellent; they include some recent 



photographs of comets and nebulae, and planetary drawings 



by Antoniadi, Phillips, Bolton, and so on. It is a little 



disappointing in the text to find the very important astronomical 

 progress of the last twenty years passed over so briefly ; most 

 of the book might have been equally well written thirty years 

 ago. There are also not a few inaccuracies. Thus on page 

 56 we have the old suggestion that the numerous satellites of 

 the remote planets compensate for the diminished sunlight, 

 though it has often been shown that the combined light of 

 Jupiter's or Saturn's moons falls far short of the light of our 

 Moon. On page 59 the axial poses of Venus and Neptune are 

 almost certainly erroneous. The latter is the pose of the 

 satellite's orbit, which is inclined some twenty degrees to the 

 primary's equator. Page 62, line 17, for axis-minor read 

 major. Page 64, the daily distances travelled by the planets 

 ought all to be doubled. Page 73, the light of Venus at 

 maximum is said to equal that of Sirius; it is really some 

 fifteen times greater. Page 83, Deimos, Phobos are generally 

 taken to be the attendants of Mars, not his steeds. The 

 original (Iliad XV, 119, 120), perhaps admits either inter- 

 pretation : 



'fis <paro, Kai p Itttovs kc\eto detftov re (pofiov re 

 Zei'71'ii^ei', at'TOS 8'evre edvffero irafAfpavouvTa. 



Which Pope translates — 



With that he gives command to Fear and Flight 

 To join his rapid coursers for the fight'. 



Page 84, line 5, for Venus read Mercury; line 12, for five 

 thousand read four thousand three hundred. Page 90, 

 line 26, for one hundred and ninety-four thousand read one 

 hundred and eighty- six thousand three hundred and twenty- 

 six ; line 32, for 60" read 46". Page 106, the words about the 

 suspected ring of Neptune and the guarded language about 

 the existence of the satellite might have been written 

 about 1850; they are ludicrous now. Page 118: it is 

 misleading to say that the Saros brings back solar eclipses 

 to the same regions after eighteen years. The region is 

 shifted 120° westward, but in the case of eclipses near the 

 poles the two tracks may overlap. The tracks are said to 

 move southward after a saros ; this is only true for ascending- 

 node eclipses ; in descending-node eclipses, of which 1914 is 

 one, they move northwards. Page 128, the shadow in 1914 

 travels from Norway to Russia, not vice versa. Same page, 

 the map in Oppolzer's " Canon of Eclipse" is quoted as evidence 

 that the eclipse of 1999 will not be total in Cornwall. But the 

 maps in the Canon only represent tracks of eclipses as circular 

 arcs, which do not claim to be accurate. Calculation shows 

 that the eclipse will be total in Cornwall. 



Page 195 footnote, Sigma Octantis is stated to be some 

 distance from the south pole ; it is really only three-quarters 

 of a degree distant, much nearer than our Pole Star. Page 200, 

 no mention is made of the very important double-star work 

 done at Greenwich. Page 214, the eclipse theory of Algol is 

 no longer merely a suggestion, it is demonstrated fact; the 

 secondary minimum, when the fainter star goes behind the 

 brighter, has been detected by Stebbins. Page 232, the 

 phrases " White " and " Green " nebulae, objected to by the 

 author, are used to denote a very real difference of spectrum. 

 Page 323, axial rotation, for days, hours, minutes read hours, 

 minutes, seconds. It seems rash to give the short rotation 

 periods of Mercury and Venus without query, considering how 

 many astronomers support the long periods. Curiously 

 enough, the Canadian Handbook noticed below gives the 

 long rotation periods without question. The safest attitude 

 seems one of suspended judgment, the evidence being con- 

 flicting. Page 324, the period of Jupiter VII should be 

 260 days, of Jupiter VIII 738-9 days, not twenty-six months. 



In conclusion, we may state that the chapter on the 

 construction of a small observatory is written with practical 

 experience, and is likely to be very useful. ^ ^ ^ q 



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