April 19, 1917] 



NATURE 



H5 



Aveary business of putting on the hands eleven hours 

 and waiting for seventy or more strikes. 



(4) When the clock is thus adjusted, one would see 

 aX a glance whether " summer " or normal time is 

 being registered on his clock. At present we have no 

 means of knowing from the clock itself which time 

 is indicated. 



Clock-makers might be well advised to initiate this 

 simple change. I, for one, would certainly choose a 

 clock of the type suggested, which, used as I urge, 

 would obviously be less liable than on the present 

 plan to injurv at the bi-vearlv adjustment. 



P. E. Shaw. 



AEROPLANES AND PROPELLERS.^ 



i) /^ONTRARY to its title, the first quarter 

 ^-^ of Lieut. Turner's book is devoted to 

 the aircraft of yesterday. The early mythical 

 attempted or pretended flig^hts attributed to such 

 historical characters as Leonardo da \'inci, Dante 

 of Perugia, Besnier, Barthelemy Lourenco, and 

 others have always afforded entertaining- reading^. 

 A book which starts with these exploits and 

 traces the development of the airship and aero- 

 plane past Montgolfier's discovery of the balloon 

 and the aeroplane experiments of Lilienthal, 

 Pilcher, Chanute, and Wright down to the 

 present war cannot fail to be of interest. 



It may safely be said that the author has been 

 very successful in an attempt to concentrate the 

 maximum amount of information in the minimum 

 amount of space. Ever\- page is full of facts, yet 

 the book is quite readable and interesting. Much 

 of the subject-matter will probably be new even 

 to the great majority of experts; for instance, the 

 altitude charts of the first historic balloon journeys 

 from London to Russia and Sweden. The 

 chapter on meteorology, too, contains a number 

 of interesting tables of statistics relating to atmo- 

 spheric conditions at different altitudes. 



Modern aeronautical theory and practice may 

 be said to occupy about 130 pages of the whole 

 book, and this section contains interesting 

 chapters on "Learning to Fly," "Sensations 

 during Flying," and "Sensations during Balloon- 

 ing." The remainder of the book is mainly taken 

 up with aircraft in war, and undoubtedly will do 

 much to enlighten the British public on matters 

 which everyone ought to know. For example, 

 on p. 242 : — 



" In anti-aircraft w-eapons Germany led the way 

 and had done so for many years. The French 

 were, however, in a strong position when the war 

 broke, out. Great Britain had done little save 

 feed on illusion until a few months before the 

 war, and for many months after deficiency in this 

 respect was only too conspicuous." 

 -., But the most notable feature of this section is 

 the chronicle of thrilling feats and adventures in 

 the great war. Bomb-dropping on railways and 

 on submarines, duels in the air, and seaplane 

 [adventures give some idea of the more exciting 



t 1 (1) '• Aircraft of lo-day : a Popular Account of the Conquest of the 

 [Air." By Lieut. C. C Turner. Pp.315. (London : Seeley, Service and 

 tCo., Ltd., 1917.) Price5j.net. . ^ „ „ ,„ 



\ (2) "Notions generalessurlesAppareils a Reaction. Par Paul Popovati. 

 LPp. 36. (Paris : Gauthier-Villars; n.d.) 



NO. 2477, VOL. 99] 



contents of the book, while, on the other hand, 

 the possibilities and limitations of a'urcraft in war 

 are subjects on which the author expresses well- 

 considered opinions. 



.\n intelligent reader would not, naturally, turn 

 to a book of such a character for information on 

 the more theoretical aspects of aeronautics. It 

 is, however, to be regretted that the few refer- 

 ences to the principles of mechanical' flight are so 

 fragmentary' and one-sided that it would have 

 been far better to leave them out altogether. 



The constantly recurring references to stability 

 cause that subject to assume an exaggerated 

 degree of importance for which there is no his- 

 torical • justification, since inherent stability has 

 played no part whatever in thepractical evolution 

 of the aeroplane except in its most recent im- 

 provements. Moreover, the definition of stability' 

 (p. 299) is incorrect, and on-p. 139 Mr. Turner 

 confuses the centre of pressure with the area of 

 maximum pressure. On the other hand, the 

 author fails to appreciate the fundamental import- 

 ance of Langley's work in show-ing that for small 

 angles of attack the air-pressure on an oblique 

 lamina is far in excess of w hat it would be accord- 

 ing to Newton's hypothesis. Had it not been 

 for "Langley's law" modern feats of aviation 

 would have been impossible. The next step was 

 the improvement of light motors and propellers, 

 on both of which subjects fuller statistical in- 

 formation would be of much more use than these 

 scrappy attempts to discuss a" highly technical 

 question like stability. Moreover, we greatly 

 doubt whether the systems figured as illustrating 

 " inherent stability " have ever been proved to 

 satisfy the requisite conditions. Many of them 

 were certainly designed long before the experi- 

 ments at the National Physical Laboratory 

 rendered any such test possible. 



These remarks apply in particular to certain 

 systems on the type of the " Dunne " aeroplane, 

 in which the angle of attack is negative at the 

 tips of the wings. These may very probably be 

 iiJierently stable, but the performance of a circular 

 flight without touching the controls is no test of 

 this property; sometimes the reverse. What is, 

 however, evident is that the main effect of such an 

 arrangement is to reduce the tendency to excessive 

 banking in turning curves, and Mr. Bairstow, 

 writing in the Aeronautical Journal, has expressed 

 the view that a machine w'hich turns without bank- 

 ing is unnecessary and undesirable from practical 

 considerations. 



A very short concluding chapter deals with 

 "Flying Developments in Sight." It is interest- 

 ing that no opportunity has yet arisen for testing 

 the uses of the aeroplane in peace times. One 

 application suggested by Mr. Turner is certainly 

 promising, namely, exploration of unknown 

 countries, and, in addition to the list of places 

 which he mentions, we may not improbably live 

 to see frequent air excursions to an hotel at the 

 North Pole ! 



(2) M. Paul Popovatz's paper on "Reaction 

 Apparatus " deals only with considerations of the 



