NA TURE 



[Decemker 24, igo8 



which were subsequently found to be the intermediary 

 for the transmission of the remittent fevers, caused by 

 the presence of spirochaetes in the blood, of man in 

 Africa, and of domestic fowls in various countries. 



For those who are not experts on ticks, but are 

 made practically acquainted with them from the 

 patholog-ical point of view, a comprehensive mono- 

 graph or handbook of the group has become an urgent 

 requirement, and this need will now be supplied 

 by the monograph of the Ixodoidea which is being 

 produced by Messrs. Nuttall, Warburton, Cooper, and 

 Robinson. Part i., dealing with the Argasidae, has 

 appeared, and consists of 104 pages (not including the 

 bibliography of 18 pages), with three plates and 114 

 text-figures. This monograph will undoubtedly be a 

 most useful publication, and it is to be hoped that this 

 example will be imitated with respect to other groups 

 of blood-sucking invertebrates. A modern compre- 

 hensive monograph of leeches, for instance, is also a 

 work urgentlv needed by those who desire to study 

 the transmission of the blood-parasites of fishes and 

 lower vertebrates. 



Who's Who, 1909. Pp. xxiv+2112. (London: A. and 



C. Black.) Price \os. net. 

 Who's Who Year-Book for igog. Pp. vi-l-154. 



(London : A. and C. Black.) Price is. net. 

 The EnglisJm'oman's Year-Book and Directory, igog. 



Edited by G. E. Mitton. Pp. xxvi-l-372. (London : 



A. and C. Black.) Price 2s. 6d. net. 

 The Writers' and Artists' Year-Book, igog. Pp. vii + 



121. (London : A. and C. Black.) Price is. net. 

 These four works of reference are so well known and 

 widely esteemed that it is hardly necessary to say more 

 than that each maintains its high level of excellence. 

 "Who's Who" continues to increase in bulk; this 

 vear there are 72 pp. of additional matter, indicating 

 the editor's desire to make his roll of honour as com- 

 prehensive as possible. 



The " Who's Who Year-Book " is made up of the 

 tables which were formerly published in " Who's 

 Who," with many new lists, including, we notice, one 

 of the Nobel prizes awarded since 1901. 



Every particular of importance about the useful work 

 women are doing is to be found in the " English- 

 woman's Year-Book and Directory"; and as the 

 Editor remarks, " no woman who takes any part in 

 public or social life can afford to be without it." 

 Even a glance through the volume will serve to show 

 that women are making notable contributions to 

 knowledge, and taking an honourable part in every 

 form of activity intended to improve the conditions of 

 human life. 



The title of the fourth year-book sufficiently describes 

 its scope ; the volume should prove of great assistance 

 to young writers and artists. 



Arcana of Nature. By Hudson Tuttle. With an In- 

 troduction by Dr. Emmet Densmore. Pp. 471. 

 (London : Swan Sonnenschein and Co., igo8.) 

 Price 6s. net. 

 Dr. Densmore's introduction includes memoirs of 

 Emanuel Swedenborg, A. J. Jackson, Hudson Tuttle, 

 Cora Richmond, and W. J. Colville ; and this fact— - 

 since all are described here as " psychics " — will 

 serve to indicate the scope and character of the volume. 

 " The Arcana of Nature " was published in i860, and 

 its subtitle, "The History and Laws of Creation," 

 shows its ambitious aim. Dr. Densmore has been irn- 

 pressed with the phenomena to which attention is 

 directed in this volume, and he feels they deserve con- 

 sideration " from the psychic student as well as from 

 the general public." 



NO. 2043, VOL. 79] 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with tlie -writers of, rejected 

 manuscripts intended for this or any other part 0/ Nature. 

 No notice is taken of anonymous communications.] 



Flying Machines and their Stability. 



In the early part of this year I suggested in a letter 

 to N.4TURE (vol. Ixxvii., p. 293, January 30) that it would 

 be desirable for experimenters with flying machines to 

 direct their attention to automatic stabilising appliances, 

 and the character of the accidents which have occurred 

 since that letter was written tends to emphasise the 

 importance of this. 



Among the six degrees of freedom possessed by any 

 body free to move in three dimensions, viz. x, y, s, 6, ^, 

 i^i (.V being horizontal in the direction of motion, y and 2 

 horizontal and vertical, and 9, <j>, i^ angular velocities 

 about X, y, and 2), i, i', and i may be controlled by hand, 

 but for steady motion it is requisite that <j> and >)/ should 

 be zero except when the course is changing, and 8 should 

 be zero except when the horizontal curvature of the course 

 is changing. 



Of these angular velocities, any of which may be caused 

 by instability, d is the most dangerous, and it is to the 

 automatic extinction of this that attention should be 

 directed in the first place. (This is the form of instability 

 which most kites suffer from in strong winds.) 4' may 

 be a source of danger if the pitching or diving is con- 

 siderable, but i|', which corresponds to a wandering course 

 in the horizontal plane, may be dealt with by steering. 



There can be little doubt, I thinl<, that for aeroplanes 

 the best method of correcting for 6 is that adopted by 

 the Wrights, namely, the alteration of the relative in- 

 clination of the wing surface on either side. In this they 

 are following the practice of the long-winged birds, but 

 the control should be automatic. 



Automatic control of the wing surfaces could be effected 

 by any device which would copy with power the position 

 of a short pendulum without exerting any force on the 

 pendulum itself. 



The pendulum must be short, because 8 must be re- 

 lated, not to the absolute vertical, but to the direction of 

 the resultant of gravity and the centrifugal force due to 

 the horizontal curvature of the course (whatever that may 

 be), and a pendulum with a short period and considerable 

 extinction sets itself very quickly in this direction. 



It may be remarked that the same class of device could 

 be used for the automatic control of <j>. The problem here 

 presented offers a large field for invention. 



Too much stress is often laid on the particular forms 

 given to the wing surfaces. In reality, flight is possible 

 with almost any form of wing if appropriate surface speeds 

 are used. 



In nature flight is conducted in two ways, of which, 

 among birds, the albatross and humming-bird may be 

 cited as extreme examples. With the first of these the 

 body speed must be high, and much power has to be 

 exerted in starting before the economical speed is reached. 

 With the latter the body may be stationary, but the wing 

 speed is always high. 



This type of flight corresponds to " lifting screws " on 

 a flying machine, and with this form, I believe, no success 

 has hitherto been achieved. It seems not impossible, how- 

 ever, that with proper balancing appliances it will 

 ultimately prevail, considering what great advantages it 

 offers in the matter of starting and stopping. In the 

 matter of economy of power, also, it is obviously better 

 to use, if possible, the same surface both for support and 

 propulsion rather than separate propellers as aeroplanes 

 must do. If the aeroplanes could propel themselves by 

 flapping their wings, the latter objection would not apply. 



.A. Mallock. 



6 Cresswell Gardens, S.W., December 16. 



