the waters of Lake Baikal to a max-| upon, were required, and they were imum depth of seven feet. The great given in the epoch-making work of earthquake of Middle Japan in the year Suess, "The Face of the Earth. The 1891 had again the same character. It "local dislocation" theory is fully was found that a rent was opened in endorsed by Suess; but these dislothe superficial strata for a length of cations themselves are treated as but more than forty miles, and that on one separate instances of the activity of side of the rent the strata had subsided those " tectonic or building forces by as much as twenty feet in the places which continually re-model the earth's of maximum subsidence. And all in- surface, create the abysses of the dications agreed in pointing to this rent oceans and the depressions of the conas the line from which the earthquake tinents, and lift up the highest mounwaves had proceeded, so as to leave no tains. Starting from the idea that the doubt as to the subsidence being the cooling of the globe results in a steady cause, and not the consequence, of the decrease of its diameter, aud conseearthquake. Moreover, in this case, quently in a continuous shrinking and as in all others, after the sudden sub- shrivelling of its outer strata, Suess sidence had provoked several severe endeavored to show how this process shocks, thousands of smaller shocks, would work in producing the leading proceeding from the same locality, con- features of the earth's surface. He tinued to be noticed for a year or so, described how large areas have been, until a succession of smaller subsi- and are still, sinking bodily, producdences had brought the displaced mass ing the great faults which intersect to a rest. The great earthquakes which our rocky formations; how semicircuaffected in April last the north-eastern lar depressions arise on the borders of region of continental Greece had the the highlands; and how the lateral same character. A great fissure thirty-pressures developed during the shrinkfive miles long was opened, and on one side of the fissure the Plain of Atalante was lowered and slightly shifted towards the north-west; and similar, although submarine, changes of level were observed during the earthquakes which visited Zante and the Gulf of Corinth in 1873, 1886–90, and April, 1893.4 ing of the outer layers result in lateral pressures which fold the strata and lift them into mountain chains. The earthquakes under this broad conception of "geo-tectonics" appear as simple trepidations of the soil by which the shrinking of the crust and mountain-building processes are necessarily accompanied. For almost every great earthquake Kant had already remarked that most which has taken place during the last earthquakes take place on the seaboard. thirty years the cause was found in local Modern research fully confirms this dislocations and subsidences. But view, and goes a step further. It while our knowledge of the local causes maintains that by far the greatest numwas thus progressing, the part which ber of earthquakes - perhaps ninety belongs to earthquakes in the general per cent., as Professor Milne says life of the planet was lost sight of. Some broader generalizations, the necessity of which Humboldt insisted - originate beneath the sea, where the rocks, under the superincumbent hydrostatic pressure, are continuously saturated with moisture, and can the easier be displaced. In fact, in nearly 2 B. Kotò, "On the Cause of the Great Earth- every earthquake in Japan, the centre quake in Middle Japan in the year 1891," in Jour-of disturbance of which could be deternal of the College of Science, Tokyo, 1893. 1 Orloff and Mushketoff's Catalogue, St. Petersburg, 1893. 3 S. A. Papavasiliore, "On the Earthquake of Locrio of April, 1894," in Comptes Rendus, 1894, cxix. 112, 380; analyzed in Nature, 1. 607. 4 W. G. Forster, in Mediterranean Naturalist, April, 1893; analyzed in Nature, April 27, 1893, xlvii. 620. mined, it was found to lay a short distance off the eastern coast of Nippon. 5 Ed. Suess, "Das Antlitz der Erde." 2 vols. Prague, 1885. This work of first importance has not yet been translated into English. The same is true of the earthquakes another condition for frequent earthwhich have lately visited Greece, as quakes. illustrated by the breakages of subma- But even in this form the law would rine cables, which undoubtedly indicate not be complete, as it would not inthat considerable changes of level have clude the disturbed regions of the contaken place at the bottom of the sea.1 tinents; and it is most remarkable And the same is true, again, of the that, when worded accordingly, it apConstantinople earthquake of July last, plies to continents also. In the very which had its centre of disturbance in heart of Asia there are two regions the Sea of Marmara, at a short dis- where earthquakes are especially fretance from San Stefano.2 In short, it quent, and both of them lie along the may be taken as a fact that a great steep north-western border of the number of earthquakes, to say nothing| Great Plateau of Central Asia, where it of the sea-tremors, which also are nu- abruptly falls from the heights of the merous, originate at the sea-bottom, near the seacoast. Tian Shan to Lake Issyk-kul, and from the heights of the Khamar-daban However, not all seacoasts are (about eighty-five hundred feet high) equally liable to be visited by earth- to the seven hundred and fifty fathoms quakes. The flat lands of subarctic deep Lake Baikal. A third depression Asia, which gradually merge into the of the same kind also a hearth of shallow Arctic Ocean, are seldom dis-earthquakes — is situated on the northturbed. A steep slope of the sea-east border of the plateau of Persia and bottom itself, or of an elevated land Armenia, where the fifteen thousand towards a deep sea, is a necessary con- niue hundred feet high Savelan rises dition for both earthquakes and sus- over the deepest parts of the Caspian tained volcanic action. The eastern Sea, marked by the five hundred fathcoasts of the Japanese archipelago, oms line; while farther west we have which face the till lately unfathomed the depression of Vienna, lodged beabysses of the Northern Pacific, and the abrupt slope of the Chilian coast of South America, are well known instances in point. tween the north-eastern Alps and the north-western Carpathians, which has been so well described by Suess as another centre of earthquakes. MoreThe deep depressions of the bottom over, the three first-named depresof the east Mediterranean, where a sions, like the so much disturbed depth of over two thousand fathoms Gulf of Tokyo, or the Bay of Arauco is found within twenty miles from the in South America, are semicircular island of Rhodes; the western coast of depressions, carved out in the edge Southern Greece, facing the twenty- of the highlands; and this further one hundred and seventy fathoms deep confirms the above-mentioned views abyss of the Ionian Sea which sep- of Suess. arates it from Sicilia; the Neapolitan coast, separated by but a hundred miles from the two thousand fathoms depth of the Tyrrhenian Sea; and so on-all these facts enable geologists to formulate another law, namely, that steep slopes, either from the land to the sea or of the sea-bottom itself, are However, a further step seems to be required in the development of the hypothesis. The most severe earthquakes undoubtedly take place on the borders of high plateaus, whether these plateaus slope towards the ocean, or whether they rise over flat lowlands surrounding them. But all plateaus are fringed by border-ridges, which gently rise over their elevated surfaces all along their edges, as well as on the edges of the separate terraces which are so frequent in the plateaus of Asia This feature is too genand America. eral to be merely accidental, although it has hitherto remained quite unex- which aeronautics is discussed in a plained. It is therefore possible to scientific spirit.1 suppose that the subsidences which The services rendered by balloons known, and since that time steady progress has been achieved both in the mode of construction of balloons and the art of aerial navigation.2 take place, chiefly along the borders of during the last Siege of Paris are well the plateaus, must have a double effect | -that of lowering the levels of the surrounding lowlands or plains (or of the adjoining sea-bottom), and of lifting up at the same time the tops of the By taking advantage of the different inclined strata; this process, repeated directions of wind at different heights, for ages, resulting in the formation of which begin to be better known, and the border-ridges, which are a neces- may be ascertained by means of pilot sary accompaniment to all plateaus of balloons, the navigator to some extent the Old and the New World. And as chooses his own direction; and with these border-ridges mostly are, or have the new anchors and guide-ropes landbeen in recent geological times, the ing, which is the most dangerous part seats of intense volcanic activity, we of ballooning, has been so much simplisee that earthquakes and mountain-fied that balloon trips are now as safe building are thus brought again into as any other kind of sport. For meconnection. But this hypothesis, which I venture to add as a further extension of Suess's views, lands us on a new domain the origin of mountains which may be better treated separately on some future occasion III. teorology the balloon is a precious aid, aud a good deal has been learned from the aeronauts about temperature and electricity in cloudland; while unmanned balloons, provided with selfregistering instruments, as has been found by M. Hermite, can bring us down the most precious information from those highest strata of the atmosphere in which Mr. Glaisher nearly lost his life. The idea of adding a propeller to a balloon, and thus enabling it to navigate close to, or even against, the wind, is certainly not new-Girard had already realized it in 1852 - but the practical application of his idea had to contend with many technical difficulties. The deformation of the balloon, which takes place as soon as it begins to progress against the wind instead of being carried with it, had to be prevented; a light but powerful motor had to be devised under the limitation of employing no fire for it; and a number of minor obstacles had to be over GREAT hopes have been revived again among aeronauts by the experimental flights of Dr. Lilienthal in Germany, and the partial successes obtained with their flying-machines by Messrs. Maxim and Phillips in this country, and Mr. Hargrave in Australia. For more than a half-century inventors in aeronautics have been treated as foolish dreamers, and no later than two years ago an American professor who wanted to address his students on the subject of mechanical aviation felt it necessary to seriously beg his audience not to interpret his choice of the subject as a token of declining mental faculties. But, happily enough, these dark times are over, and aeronautics is becoming a regular department of scientific research. The general revival of science which we witnessed in the early sixties has given new life to this branch of research, and we have now an excellent scientific lit-ica. And so on. erature devoted to the subject, several aeronautic societies (one in Great Britain) which are doing excellent work, and several reviews in the pages of 1 L'Aéronaute is published at Paris since 1869. The Zeitschrift für Luftschiffahrt und Physik der Atmosphäre is a sister review to the Zeitschrift für Meteorologie, and is published by the German and Austrian Aeronautic Societies. A new review, the Aeronaut, has been started this year in Amer 2 For the technical part of the subject and the succession of invention, see the new book of Mr. Chanute, "Progress in Flying Machines," New York, 1894. Also his address before the Congress of Aeronautics at Chicago. come. Accordingly, although propelled | pleted his work ere it was forgotten. balloons are now the pets of the minis- The wonderful observatious and phystries of war in the big States, and ical reasonings and experiments of money is freely spent upon them, the Leonardo da Vinci had to be re-discovadvance is still very slow. The great- ered a few years ago.2 Even the adest speed ever attained by the French mirable work of Borelli, who wrote on officers Renard and Krebs with their the flight of birds in 1680, and the very cigar-shaped balloon, propelled by a valuable researches of Silberschlag, storage-battery motor, was only four-published in 1783,8 were little known; teen miles to the hour. True, that nay, even the work of Cayley, which even with this modest speed the bal- dates from 1796, had fallen into oblivloon could be navigated in a feeble ion. Modern science had thus to begin breeze, so as to return to its starting- anew, and it began by dismissing, first, point, after having described a trian- certain prejudices which had taken gular route; but in order to brave the hold of most minds. wind a speed of fifty miles is required, One of these prejudices was to beand all that the French officers expect lieve that the warm gases contained in from their new balloon is a speed of the cavities of the bird's body and its twenty-five miles, which will enable it quills render it lighter than an equal only to take tacks in a moderately fresh volume of air. Every one can, howbreeze.1 Moreover, there being but ever, calculate how insignificant the little hope of discovering a gas the effect of that warm air must be; density of which would be still smaller and every one knows that a than that of hydrogen, the dimensions which has been wounded on the wing of a propelled balloon must remain falls at once to the ground. This very great, in proportion to the useful prejudice could easily be discarded; weight it can carry. The new French but another, as to the immense force balloon (as remarked by Mr. Chanute) which the bird is supposed to develop will be of the size of a river steamer, during its flight, is much more difficult and yet it will hardly carry more than to get rid of. No amount of evidence, four passengers; and a further in- borrowed from what every one can crease of size would be of little avail, verify by dissecting the muscles of a in proportion to the cost of the ship. bird, or by observing the ease with Consequently, scientific research and which it flies, could overthrow that invention are now directed more and very common error, supported by the more towards the flying machine, most fallacious calculations of a French which, being much heavier than an mathematician made in the early part equal volume of air, will find in its very of this century.5 It took Professor S. density and inertia the means of con- Langley in America nearly four years of tending against the currents of air. careful experiments to show how erroneous were both those calculations and the data upon which they were based. We have under our very eyes a most perfect flying-machine the bird and we have only to study, from a physical point of view, the laws of its flight, in order to find out the laws which must guide us in our schemes. This is what science has tried to do ever since the time of Leonardo da Vinci. But, owing to a want of interest in such researches in the general public, the scientist had hardly com 1 It is two hundred and fifteen feet long, and forty feet in diameter. The motor, forty-five horse-power, will weigh, with fuel for ten hours, thirty-four hundred pounds. bird nard de Vinci," in Revue Scientifique, mai 28, 1892, xlix. 687. 2 Amans, "La Physiologie du Vol d'après Léo 3 Schriften der Berliner Gesellschaft der Natur freunde, Bd. il. 1781-1784. 4 Its effect can counteract but one fifty-thousandth part of the weight of the bird (Marey, Le Vol des Oiseaux, p. 287). tained that in order to sustain itself in the air a swallow spends a force of one-seventeenth of a horse-power. Langley found that force fifty times smaller. Even the calculations of Babinet, a supporter of aviation, were quite erroneous, as shown by Marey (Le Vol des Oiseaux, p. 328). Navier, (Mémoires de l'Institut, ii. 1829) maiu S. P. Langley, in Smithsonian Contributions to E Now we can at last take it as granted | without the aid of drawings, the admithat, although the energy spent by rable mechanism by which the bird birds in sustaining themselves in the drives the air with its wings (rigid at air varies a great deal according to their shapes and manners of flight, it is less than one one-hundredth to two one-hundredths of one horse-power for each two pounds of body weight. And, as art has already succeeded in producing small prime motors whose weight does not exceed ten pounds per horse-power, one sees at once that the problem to be solved by the flyingmachine offers no mechanical impossibility, provided we learn to utilize the energy of our motor as well as the birds utilize their forces. T. the front edge and flexible at the back), compresses it, and has only to progress forward in order to sustain itself in the air in spite of the action of gravitation. This must be read in the above-named works and seen on Marey's photographs. But what must be said is, that a continuous rotatory movement being more advantageous in a machine than a mechanism which would be an imitation of the flapping of the wings, the best form to be given to a screw-propeller which has to act in the air was indicated by such investi nardo da Vinci, and worked out by The next step to be made is, accord-gations. It was found already by Leoingly, to learn from the birds how best to utilize the force of a motor, and therefore to study the mechanical details of birds' flight. Science has done this well, and we have already most excellent guides for this part of the problem in the works of the Duke of Argyll, Mr. Pettigrew, Mouillard, and the fundamental work of Marey (Le Vol des Oiseaux), in which last all such problems have been treated with the aid of instantaneous photographs, taken at intervals of small fractions of a second, not to speak of many others, each of which contains some valuable information. It would be impossible to describe here in a few words, and Knowledge, 1891, p. 801; and American Journal of Science, November, 1891. Also Lord Rayleigh's discussion of the same in Nature, December 3, 1891 (xlv. 108), where indications to the works of Mr. Wenham and Mr. W. Froude will be found. 1 The chapter devoted by the Duke of Argyll, in his "Reign of Law" (first edition, 1866), to the flight of birds is a masterly work, based upon his and his father's observations, and imbued with a thorough knowledge of nature. The same qualities will be found in the more exhaustive works of Mr. Pettigrew (Animal Locomotion with a Dissertation on Aeronautics, London, 1873) and Mouillard (L'Empire de l'Air: Essai d'Ornithologie appliquée à l'Aviation, Paris, 1881); while the large work of Marey (Physiologie de la Locomotion Le Vol des Oiseaux, Paris, 1890, which must not be confounded with his earlier work) is an exhaustive treatise, based upon observations made with the aid of chronophotography. Some of the earlier works are already named. See also Lilienthal's "Der Vogelflug als Grunalage der Fliegek unst,' Berlin, 1889; T. d'Esterno, "Du Vol des Oiseaux," Paris, 1864; Goupil, "La locomotion aérienne," Charleville, 1884, etc., each of which contains valuable observations. We all know, indeed, that most birds, before they can rise in the air, must acquire a certain horizontal speed. Many good flyers can be kept prisoners in an open small yard surrounded by walls twenty feet high, or even on a small open pond surrounded by low but grassy shores, upon which the bird cannot take the necessary run. But once a bird has acquired this speedand it mostly acquires it by running against the wind — it flies with a wonderful ease; its spread wings and its speed sustain it. Once in motion, the swallow and many other birds will fly any amount of time, hardly using at all their wings for flapping. 2 Mouillard (L'Empire de l'Air) has made the experiment with Procellaria. |