vector, which can have no scalar part. Again, in the formulæ of Rankine and Weyrauch. In a series Exercise (13) we have by definition of three tables the author gives the values of the earth pressure against walls of different heights as deduced by these three formulæ, and the results agree so well that it is evident that any one of the three methods is equally trustworthy from the practical point of view. The results obtained in the preceding chapters are applied in chapter iv. to the design of various types of retaining walls; and the important problem of the determination of the necessary thickness at the base of a retaining wall in order that it may be stable under where a is the length of a, and a, is the unit vector along a. Now according to Gibbs a.a=+a3, so that all the terms of the assumed expansion must be posi-earth pressure is fully discussed for each type of wall. tive. How then can they give the sine and cosine? The statements are true only if we use the Hamil tonian vector whose square is minus the square of its length. The linear vector function is introduced for the discussion of the kinetics of a rigid body. This is purely Hamiltonian, and is very good so far as it goes. The investigation, however, seems to lack here and there the strength and spontaneity of Tait's classical discussion. RETAINING WALLS AND ROAD BRIDGES. (1) Graphical Determination of Earth Slopes, Retaining Walls, and Dams. By Prof. C. Prelini. Pp. ix+ 129. (London: A. Constable and Co., Ltd., 1908.) Price Ss. net. (2) The Design of Highway Bridges, and the Calculation of Stresses in Bridge Trusses. By Prof. M. S. Ketchum. Pp. xxi+ 544. (New York: The Engineering News Publishing Co.; London: A. Constable and Co., Ltd., 1908.) Price 16s. net. (1) THIS HIS book brings together for the use of the engineering student in a handy form for reference the various graphical methods due to Culmann, Rebhann, and others, for solving problems connected with earth pressures. The first chapter treats of the stability of earth slopes; the cohesive force in a bank of earth is determined by graphical methods, and hence is deduced the most probable plane of sliding; by means of the parabola of cohesion the various slopes of equilibrium for various heights of bank are determined, and its application to practice is then discussed; the considerable economy in excavating deep trenches with slopes correctly designed is proved by worked out examples. In the second chapter the design of retaining walls is taken up; the author points out that all the various theories which have been employed can be divided into two groups, (a) those depending on the theory of the sliding prism, (b) those depending on analytical theory. A graphical solution, due to Rebhann, of the sliding prism type is then given; this method is then applied to a series of practical cases, both for retaining walls when surcharged, and when free of surcharge. The variation of pressure with height of wall, and position of the centre of pressure are dealt with, and also the effect of cohesion on the pressure against retaining walls, and the pressure of passive resistance of the earth in the case of abutments which are pushed outwards by arches. In the next chapter there is an analytical demonstration of Rebhann's theory, and brief statements of The last chapter of the book is devoted to masonry dams, which, as the author points out, are simply a particular case of retaining wall, with the material sustained practically frictionless; it is shown that the most economical profile, theoretically, is a triangular one, but in practice this is an impossible section. The modification needed in order that the dam may have a certain thickness at the top is then discussed, and the pentagonal profile deduced. It is shown that this theoretical profile is the basal form of all modern high dams. The book should prove especially useful to civil engineering students during their final college year. (2) While many text-books have been devoted to the design of railway bridges, but little attention has been hitherto given to the equally important question of the design of road bridges, and, although the work of calculating the stresses in the different members is the same for both types, there are, owing to the very different requirements to be met, radical differences in the design of the two classes of bridge. This book, therefore, meets a distinct want, and it will be especially useful to the young designer, in view of the fact that the author has given special attention to the problem of the design of the substructure, which is usually quite neglected in books on bridge design. An entire chapter has been devoted to the design of floor beams, floors, shoes, and pedestals, and other similar details, and it is in regard to such matters that the young engineer most commonly finds the need of help and guidance. The ninth chapter will prove of considerable use, not only to the student, but also to the teacher; as the author points out, in order to obtain a thorough knowledge of the calculation of stresses in bridge trusses, it is essential that the student should work through numerous problems-altogether twenty-four problems are worked out in detail in this section of the book, and a second similar one has been added to each of the twenty-four problems as a further exercise for the student to solve with the help afforded by the worked-out example; some of the solutions are obtained graphically, others by algebraic methods. Another valuable section is that devoted to influence diagrams, or influence lines, which are required in studying the variation of the effect of a moving load or system of loads, on a truss. Special attention has been given to the design of high truss steel bridges, and to plate girder bridges, and this section of the book is well illustrated with reproductions of working drawings, which, in spite of the necessary small scale, are perfectly clear and distinct in all the essential details. The stresses in, and the design of, solid masonry arches and culverts form the subject of two chapters, and, though there is nothing specially novel in the treatment adopted, these sections of the book will be welcome to the draughtsman who is engaged in this branch of bridge design, especially as the author has given some useful notes on the theory of reinforced concrete. In part iii. of the book there is a full critical investigation of an existing structure-the weights, costs. and efficiencies of the members of a Pratt highway bridge of 160 feet span are fully worked out, and the errors in design pointed out, and the modifications which would improve the design are suggested. There is no doubt that such an investigation is bound to make students familiar with bridge details, and we would commend this method to the notice of engineering teachers. T. H. B. OUR BOOK SHELF. Die Strahlen der positiven Elektrizität. By Prof. E. Gehrcke. Pp. xi+124. (Leipzig: S. Hirzel, 1909.) Price 4.50 marks. AT a moment when scientific thought is being concentrated on the consideration of the nature of positive electricity, we can only welcome the appearance of a book which aims at bringing together, in the short compass of a hundred pages, all the principal facts bearing on the subject. This Prof. Gehrcke has done, and he has done it well, for, with the exception of a few slight omissions, he has put before his reader all that is essential with regard to positive rays. But we could wish that more than this had been done, for it is a little disappointing to find the results of experiments given, often with little, if anything, to indicate the theoretical deductions which can be drawn from them. Indeed, not infrequently the opinions of different investigators as to the interpretation of the results of experiments are recorded without any comment as to the relative merits of rival theories. No doubt it was the intention of the author to keep the work within definite limits, but it seems that much has been sacrificed merely for the sake of brevity. In no part of the book is this more apparent than in the portion devoted to radio-activity and the nature of the a rays. Here descriptions are often so short that it is questionable whether anyone not already fully acquainted with the subject will be able to follow the reasoning. In the part dealing with radio-activity there are a few inaccuracies which call for comment. On p. 90 the author states that it is usually supposed that one a particle is given off from each atom during any radio-active process involving the emission of such particles. In view of the work of Bronson, who showed, for example, that an atom of thorium emanation, in breaking up, gives off four times as many a particles as an atom of thorium B or C, this is clearly not the case. Again, the table on p. 89 contains some mistakes. The volatilisation point of radium A, given as 1000° C., is too high, and that of radium C, as 1100° C., is too low. The volatilisation point of radium B is given as 20° C., instead of 600° C. That radium B can escape, at ordinary temperatures, from a surface coated with active deposit is correct, but the phenomenon is not due to any true volatility of the substance at ordinary temperatures, and has been explained on quite different lines. Das Seelenleben der Tiere. By Dr. P. Ohm. Pp. 117. (Stuttgart: Neue Weltanschauung, 1909.) THIS little book is the fourth of a series called "Weltanschauungs-Fragen," and apparently intended of Haeckel. Consequently, Dr. Ohm brings forward to include contributions to the monistic philosophy that it is totally different in kind from human, and the two principal theories of animal intelligence-one the other that it is the product of evolution, and differs only in degree, but is essentially of the same nature. After a brief historical introduction to the authors subject, and noticing the opinions held by various Harold Höfding, Dr. Ohm speaks of the dawning from Plato to Wasmann, Darwin, and intelligence indicated in Protista, sponges, Medusa, Hydra, molluscs, &c., and then inserts a chapter on instinct to controvert the view advocated by Wasmann that it is a perfect and divine inspiration, quite different from reason. Here he deals especially with gence of insects, especially ants and bees. the manifestations and imperfections of the intelli Another chapter is devoted to the "Seelenleben " ("soul-life," or, more correctly, intelligence) of insects and spiders, with special reference to their eyes, antennæ, sense of direction, &c., and a figure dina) using one of its own larvæ to spin threads. is given of the Indian tree-ant (Ecophylla smaragAn illustration is also given of the large garden on the senses, habits, and intelligence of vertebrate diadem spider and its web. Another chapter follows, animals, and the book concludes with a comparison between human and animal intelligence; and the author regards the faculty of speech as the essential difference between them. A short bibliography is appended. Dr. Ohm has written a thoughtful little book, and ately. has dealt with a difficult subject fairly and moderHis work will be read with interest by students interested in the important questions with by preconceived ideas, on one side or another, that which it deals; but everyone is so much influenced it is almost impossible to form an unbiassed opinion about them. 66 W. F. K. Comment Former un Esprit. By Dr. Toulouse. Deuxième Édition. Pp.. x+260. (Paris: Librairie Hachette et Cie., 1908.) THIS book is the reply to a request for ten lessons body what Dr. Toulouse's experience as a psychologist to professional teachers and parents which should emand a medical man has taught him to think essential to "the cultivation of an intelligence." He starts from a position with which critics of educational institutions on this side of the Channel have made us familiar; we teach everything in school to-day except how to think and how to act. also familiar-education should aim at teaching us His remedy is not so much to know as how to apply knowledge to achieve this end it must train us, in accordance with the regulation of the important affairs of life. To sound principles of "method" (in the Cartesian sense), to observe, to judge, to feel, to act. The author's discussion of these methodical principles is broad-minded and suggestive, but it is too brief and schematic to be of much direct service to the teacher in the class-room or the parent in the home. His recommendations have much more value when they either express the practical wisdom of a man who has managed his life successfully or deal with specific topics on which his experience as a medical psychologist gives him authority. Under the latter heading attention may be directed to a vigorous argument for the frank instruction of boys and girls in "the phenomena of life." 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 the writers of, rejected manuscripts intended for this or any other part of NATURE. No notice is taken of anonymous communications.] Visibility of Halley's Comet. THE discovery of Halley's comet at a time so far pre substance in the blood of Lernanthropus possesses one of The the properties of hæmoglobin but not the others. matter being in this unsatisfactory state, it is very should re-investigate the blood of Lernanthropus. desirable that someone, to whom the opportunity is offered, New College, Oxford. GEOFFREY SMITH. MAGNETIC STORM OF SEPTEMBER 25. ceding the date of perihelion passage adds another proof DR. CHREE, F.R.S., has sent us the following of the great capacity of the photographic method. The interesting point to many observers is as to when the comet will become visible to them as a telescopic object. This must, of course, depend in a large measure upon the diameter of their glasses and on their powers of vision. After the present moon has left the sky, say during the second week in October, the comet ought to have increased in light sufficiently for it to be observed in a 12-inch telescope. The calculated magnitude of the comet will be 14 on October 15, and its distance from the earth about 230 millions of miles. Its apparent position will then be five degrees west of y Geminorum, and near 72 Orionis. On October 16 the comet will be just two degrees south of 71 Orionis (mag. 5.5), and ought to be visible as a very faint nebulosity, especially if the night is good. The transparency of the air has an important influence on the perception and aspect of faint comets and nebulæ, for a really suitable sky will enable objects to be glimpsed which are utterly invisible on bad nights when there is diffused light, thin cloud, mist, or fog prevalent. The comet will be visible in an excellent position nearly all night during most of the winter, but will continue small and faint until it blazes out next April. W. F. DENNING. The Presence of Hæmoglobin in Invertebrate Blood. MAY I make use of your columns to correct a statement in my article on Crustacea in vol. iv. of the " Cambridge Natural History," which I am afraid may seriously mislead the reader? Referring to the alleged presence of hæmoglobin in the blood of Branchipus and Daphnia, I have stated in a footnote on p. 30 that the fact that the red blood of Lernanthropus has been proved not to contain hæmoglobin throws doubt on the reality of its presence in the other two animals. At the time of writing I was not aware that the authority on which the presence of hæmoglobin in Branchipus and Daphnia rested, and I was inclined to impugn, was Sir Ray Lankester, who, in the late 'sixties and early 'seventies, published a series of researches which laid the foundation of a comparative knowledge of the distribution of hæmoglobin and similar respiratory pigments in the animal kingdom (see especially Proc. Roy. Soc., vol. xxi., December, 1872, p. 70). After reading these articles it is clear to me that Sir Ray Lankester's statement as to the presence of hæmoglobin in the blood of Branchipus and Daphnia, resting as it does on careful microspectroscopic examination, is quite unaffected by what may or may not be the case in Lernanthropus, so that I can only withdraw my footnote with many apologies to him and to readers of the "Cambridge Natural History." With regard to Lernanthropus and its allies, small crustacea parasitic on fish and mussels, which possess a closed vascular system containing a red fluid, there is still some doubt. Van Beneden, who discovered Lernanthropus in 1880, states (Zoologischer Anzeiger, Bd. iii., p. 35) that he examined the blood spectroscopically, and found the oxyhæmoglobin lines. More recently Dr. Steuer (Arbeiten Zool. Inst. Wien, vol. xv., p. 14, 1903) sent numerous specimens of an allied form, Mytilicola, to Prof. R. von Zeynek in Vienna, who came to the conclusion that the blood did not contain hæmoglobin, since (1) with glacial acetic acid and sodium chloride no hæmin crystals were obtained; (2) after reduction with potassium cyanide and ammonium sulphide, the characteristic reduced hæmoglobin lines were not formed; (3) there was no hæmochromogen reaction. Curiously enough, we are not told whether the simple examination of the blood gives the oxyhæmoglobin lines, as Van Beneden stated, or not, so that we are left in doubt whether Van Beneden was altogether in error or the red communication on the above : The magnetic storm of September 25 exhibited the rapid oscillatory movements that are usually associated with the appearance of aurora. As recorded at Kew, the storm commenced suddenly at about 11.43 a.m. During the next nine hours there was an almost uninterrupted succession of large oscillatory movements in the magnetic curves, especially those of declination and horizontal force. The storm was of comparatively short duration, no movements of any great size being recorded after 8.30 p.m. on September 25, and by I a.m. on September 26 little trace of disturbance was left. When the storm was at its height the oscillatory photographic paper was frequently too faint to show movements were so rapid that the record left on the minute details, and the limits of registration were at times exceeded. At the commencement there would appear to have been an exceedingly rapid oscillatory movement of the declination needle, after which the needle moved to the east continuously for about 15 minutes. After the first 12 minutes, during which a movement of 72' was recorded, the trace got off the sheet, so that the full extent of the easterly drift is not shown. After a few minutes' absence the trace reappeared, but, after some oscillatory movements of the needle, the trace got off the sheet again on the same side as before at about 12.12 p.m., and remained off on this occasion for nearly 40 minutes. During the whole of this time the needle pointed at least 70'-at times, probably, a good deal more to the east of its normal position. After coming on the sheet about 12.52, the trace exhibited some minor oscillations superposed on a rapid drift across the sheet. The entire width, representing 20 7, was crossed in less than half an hour, and the trace at about 1.20 p.m. got off the sheet on the opposite side. The needle then pointed about 1° to the west of its normal position. Between 1.20 p.m. and 8.30 p.m. there were a number of large oscillations, movements of 40', 60', or more, now east, now west, taking place in the course of a few minutes. The largest of the rapid oscillations clearly shown took place between about 8.7 and 8.22 p.m., a westerly movement of 98′ being followed by an easterly movement of 84'. The disturbance shown by the horizontal-force curve was no less remarkable. The commencing movement at 11.43 a.m. went beyond the lower limit of registration, a fall of 430 7 taking place in about 10 minutes. At this time the trace was off the sheet for only about 5 minutes. After reappearing it showed large oscillations. By 12.53 p.m. it had crossed the sheet to the other side, the change of force during one period of 13 minutes being no less than 625 7. The trace was off the sheet continuously from 3.55 to 5.10 p.m., the horizontal force during the whole of this time exceeding its normal value by more than 300 7. Except when off the sheet, the trace showed continuous large oscillatory movements during the whole afternoon. The largest clearly shown was partly synchronous with the large declination oscillation near 8 p.m. already described; it consisted of a rise of 520 and fall of 710 7, all in the course of 17 minutes. The declination range, 2° 7', and the horizontal-force range, 740 y, actually recorded, represent merely the full width of the photographic paper. How much these ranges were exceeded it is impossible to say, but, judging by the look of the curves, the excess was probably considerable. The vertical-force trace got off the sheet only on one side, and this element would appear to have been less disturbed than the other two. Still, as the trace was off the sheet continuously for nearly an hour after 3.35 p.m., the chances are that the true range exceeded somewhat largely the range 530 actually recorded. The duration of the storm was comparatively short, but whilst it lasted it exhibited an energy which has been very seldom rivalled at Kew. The oscillatory movements were quite as rapid as those of October 31, 1903, and the range of the elements has probably not been exceeded during the last twenty years, not even during the great storm of February 13, 1892. time thereafter. It is possible, of course, that the external currents have partly demagnetised the earth, or at least modified its distribution of magnetism, and that there are recuperative tendencies tending to cause reversion to what is for the time being a more stable distribution; but if this be the true explanation, the demagnetising action and the recuperative tendencies are presumably in action during the course of the storm, and profoundly modify the magnetic phenomena. To many minds subscription to some theory may be a necessity for intellectual comfort, but in the case of magnetic storms reservation of judgment appears at present the more scientific attitude. or In addition to the foregoing we have received from the following communication Prof. A. Fowler, of the Imperial College of Science and Magnetic storms such as the present inevitably Technology, South Kensington:-The, pos create an interest in the explanations that have been sible occurrence of a magnetic storm and auroral advanced The display on September 24 to account for the phenomenon. was 25 suggested which was theories of Arrhenius and of Nordmann, the theories by observations of the large spot then on the sun's disc. On September 24 the spot was be the most favourable position in relation to magnetic a little west of the central meridian-which appears to disturbances and spectroscopic observations showed that it was of the same disturbed type as the spot associated with the great magnetic storm of October 31, 1903 (NATURE, vol. Ixix., p. 6). and researches of Birkeland, and the deductions made by Maunder from the Greenwich disturbances all point to the sun as the ultimate source, and to some form of discharge-ions, electrons, or such like carriers of electricity as the immediate vehicle. The electrical nature of aurora is difficult to dispute, and the fact that storms like the present appear to be invariably associated with aurora visible far outside the polar regions unquestionably supports in some ways theories such as those of Birkeland or Arrhenius. When we come, however, to details, difficulties present themselves. If magnetic storms are directly due to the electrical currents which render the upper atmosphere luminous, how comes it to pass that the visual phenomena of aurora are so constantly changing, whilst even in the most conspicuously variable of magnetic storms the larger movements of the magnets take usually 5, IO, or 20 minutes to accomplish, the force appearing to alter at a nearly uniform rate for minutes on end? The relatively gradual nature of the magnetic change is a true phenomenon-as clearly indicated by the short-period magnets of the Eschenhagen pattern, as in the larger Kew magnets with periods of 10 seconds or more. There is, again, the very remarkable fact that when we go to high latitudes, where aurora and magnetic disturbance are both almost daily occurrences, the association of the two phenomena becomes much more difficult, if not impossible, to recognise. The absence of visible aurora during active magnetic disturbances may be reasonably accounted for during the Arctic summer, when the sun is above the horizon, but it is a different matter when we find the magnets rather quieter than usual during the occurrence of a bright aurora. Unless we are to assume a fundamental difference of type between auroras presenting the same spectroscopic lines, or a variety of sources for different magnetic storms, there is a difficulty which is not easily surmounted. The only explanation that has occurred to me is the possibility that the visual phenomena may represent merely intense local concentration of electrical current, and that the main portion of the discharge frequently makes no appeal to the eye, and is of a much more steady and persistent character. Another difficulty in regarding the phenomena of magnetic storms as entirely and directly due to the action of electrical currents associated with aurora is that it is a frequent occurrence-as on the present occasion-for the horizontal force to be considerably depressed below the normal value when the storm has apparently ceased and for some considerable On Friday evening (September 24) the sky was overcast, and it did not then occur to me to test the possible presence of aurora by the spectroscope. On Saturday evening, however, although the sky was at first completely clouded over, the spectroscope gave unmistakable evidence that an auroral display was in progress. From 6.40 to about 7.30 (the sun set at 5.52), the whole sky was filled with a feeble light, with brighter patches here and there, and the characteristic green line of the auroral spectrum was seen in every zenith, but the line was easily visible over the entire direction. The greatest intensity was at first near the sky, and was even seen in the light reflected by a pocket handkerchief. This condition continued with diminished brightness until near 8 p.m. Between 8 and 9 o'clock the display was very feeble, but shortly after 9 the auroral line was again fairly distinct in a faintly luminous belt about 10° above the northern horizon. After 9.30 no evidence of aurora obtained, although the sky was then partially clear. The general distribution of the green line over the heavens in clearer skies has been occasionally noted by Ångström and others, but I have not yet found any previous record of such a wide diffusion of the auroral light when the sky was completely clouded. If wholly above the clouds, the aurora must have been of extraordinary brightness in order to produce this effect. was Besides the green line, there were three fainter nebulous lines or bands in the green and blue, which have been frequently mentioned by previous observers. A careful search was made for the red line which appears in "crimson " auroræ, but its presence was not even suspected. As to the sun-spot, there was a brilliant reversal of the C line of hydrogen over one of the umbræ when I observed it at 12.20 p.m. on September 24, and on opening the slit it was clear that this appearance was produced by a very bright overlying prominence. Reversals of the chromospheric lines b, and 1474 K were also suspected, but the observations were stopped by clouds. According to Tacchini and Lockyer, it is the prominence, rather than the spot, which should be considered as related to the magnetic disturbance. THE AVIATION. At a HE successful aviation week recently concluded at Rheims should do much to popularise aviation, if that subject is not sufficiently popular already. The large number of newspapers and periodicals devoted to aërial navigation is, however, sufficient evidence of the amount of public interest which centres round the new form of locomotion. railway bookstall at Tarbes, in the Pyrenees, a few weeks back, the present writer saw no fewer than five different papers devoted to flying machines. Possibly the number of such journals is equal to, even greater than, or at any rate comparable with, the number of successful flights that have been performed; it certainly appears as if the frequency with which a new journal comes out is not small in proportion to the frequency of aeronautical successes. Indeed, at the present rate, the assigning of new titles to these journals will soon take the form of a problem in permutations and combinations. When it is attempted to draw scientific conclusions from these successful flights there is not, after all, so very much to be said. The difference between a machine that will fly one mile and a machine that will fly a hundred miles is mainly that the latter must be able to carry a heavier load in the form of petrol or other fuel than the former. In the case of high flights the same remarks apply, though the construction of a machine which is capable of ascending or safely descending at a considerable angle to the horizon presents many points of scientific interest which, no doubt, will receive the attention they deserve sooner or later, unbeknown to the average newspaper reader. In saying that when aviation takes the form of record-breaking it ceases to be a science and becomes a sport, we are, of course, not taking into account all the work of an experimental character in the construction and perfection of motors, propellers, and aëroplanes which has to be gone through behind the scenes before the sport can be indulged in. We have, however, failed to find that any very definite and striking new result has been proved by the recent triumphs. It would seem, in fact, as if writers on the subject were directing their attention to the early history of aërial navigation to make up for the fact that there is very little to write about in a mere statement of records. Under the title of Ila, a weekly journal is appearing in connection with the International Aeronautical Exhibition at Frankfurt, of which the historical section is an important feature. It is interesting to revive acquaintance with the early, and in many cases fantastic, devices of Barthélemy Lourenço de Gusman, Besnier, Jacob Degen, Blanchard, the Minerva of Robertson, with its suspended ship and cabins, and an old cartoon of an omnibus and horses hanging from a balloon. As for Lourenço, a special number (Illustrierte Aëronautische Mitteilungen xiii, 17, Ila iii.) contains references to his exploits in view of August 8 of this year being the 200th anniversary of his supposed flight. The article by Mr. B. Wilhelm is prefaced by a short editorial note by Capt. H. W. L. Moedebeck, and seems to support the view that Lourenço actually went so far as to make a small model of a fire-balloon rise in the air in presence of the King of Portugal. Of pictures of Lourenço's grotesque and fantastic design we have two in the number in question, but in No. 10 of Ila it is pointed out that if Gusman really did fly, his ship must certainly have looked quite different. Another article dealing with the general history of aerial navigation, both past and present, forms the subject of a special number of La Nature, issued on August 21 in connection with the Rheims meeting of the following week. A useful feature is the series of illustrations, each showing in one figure a collection of the principal types of airships and aeroplanes, in much the same way that the early history of the subject is summarised in the interesting old "Tableau d'Aviation" of fame. Of these we reproduce the two illustrations of the most recent aeroplanes. The article concludes with a calendar of "the great dates of aviation," which is here given, with addition of the Rheims records : When the newspapers state that one portion of the course has come to be called "the valley of death," from the numerous wrecks that every day strew its fields, and when we refer to the accidents to Paulhan, Fournier, Blériot, and still later to the death of Lefebvre and the accidents to Lieut. Calderara, to Bossi, and to Le Blanc, it will be seen that aeroplane triumphs are being bought at the expense of many thousands of pounds spent in rebuilding completely smashed-up machines, not to mention the risk to life and limb. Of course, a considerable proportion of these accidents are undoubtedly accidents in the true sense of the word, but when we read, as we have done over and over again, that machines have suddenly stonned dead from no explicable cause, and then suddenly plunged to the ground, the idea of longitudinal instability at once suggests itself, and the obvious remedy is that aviators should wait until this subject has at least been thrashed out mathematically, or should devote a fraction of the sum they spend on repairs of broken parts to furnishing the assistance which would enable the theoretical investigations to be pushed forward without delay instead of being hung up for months at a time owing to pressure of other work. Such a course would have been by far the shortest, cheapest, and best way of disposing of one of the important difficulties connected with aviation. But what chance of success would a mathematician have if he made an appeal of this kind? The world is full of people who have made, or imagine they have made, epoch-making discoveries, and who only require funds for their development. Their effusions find their way into every journal that does not adopt the most strict censorship over the scientific value of its contributions. The time has passed when any |