Imagens das páginas

The problem of the stratification of the sun's atmosphere does not, therefore, appear to have been advanced by his discussion of the various observations.

Dr. Brester's view of the solar surroundings leads him to suppose that the concentric layers which he postulates are ellipsoidal, so that the photosphere cuts different shells in different latitudes. The fact that there is an equatorial extension of some sort is abundantly demonstrated by eclipse photographs. In the application of this view to the explanation of some of the phenomena presented by the sun Dr. Brester displays considerable ingenuity, and we may refer to some of them, as they suggest points which may have to be taken into consideration in other theories.

latitude will be accompanied by change of spectrum. It is only fair to say that the exact nature of this change has not yet been fully investigated, and hence the explanatios offered cannot strictly be put to the test. Broadly speaking, however, it is evident from what has already been said, that if Dr. Brester's view be correct, there must be a layer of unknown vapours cutting the photosphere about latitude 15° (the latitude of spots near maximum), and layers of the vapour of iron, or some of its constituents, cutting the photosphere about latitudes 5 and 30 (the latitudes of spots at minimum). Before the view can be properly tested, it is clear that we must have further knowledge as to whether the iron lines widened in spots of high latitude at the beginning of a sun-spot period are

towards the end of the period, and, so far as we know, information on this point is wanting.

The Periodicity of Solar Phenomena.-Dr. Brester first of all dismisses the suggestion of planetary disturb ances as the phenomena usually seen are too irregular to be consistent with orbital motion; and other views are also found wanting. He then shows how the second of the astrochemical principles already referred to appears to him to give the necessary explanation. As in our notice of his first essay, we may say that the main idea is that during eleven years the integrated effects of the various chemical combinations which have taken place are such as to very nearly restore the conditions which had existed at the commencement of the period Slight differences would be produced each time, so that after a long interval wide differences might be expected.

The Solar Rotation.—It is a matter of common know-identical with those widened in spots near the equator ledge that the equatorial regions of the sun, as indicated by the spots, rotate more rapidly than the regions in higher latitudes. On Mr. Lockyer's hypothesis, which supposes sun-spots to be produced by the fall of condensed materials from the cooler regions of the atmosphere, this is explained by the fact that such atmosphere is highest at the equator, and the spot-forming matter thus having a greater forward velocity previous to its descent, will have a greater angular velocity on reaching the photosphere. Dr. Brester's view is a modification of this. Taking for granted that the solar layers are ellipsoidal, and that the photosphere is an independent partially condensed shell, he points out (p. 44) that when the matter of any particular layer condenses to form a part of the photosphere, the increase of density will cause it to descend towards lower layers, and as it will retain its initial velocity, the angular velocity in its new position will be increased. In this way he explains the law of solar rotation, but on account of the absence of knowledge of the densities of the vapours near the photosphere, the question cannot be treated mathematically. On Dr. Brester's view this law applies only to the photosphere itself, the ellipsoidal layers all having the same angular velocity.

This he further applies to the reconciliation of the spectroscopic determinations of the velocity which have been made by Dunér and Crew. Dunér's observations practically confirm the law derived from the observations of spots, while those of Prof. Crew show no change of velocity with change of latitude. Dr. Brester points out that most of the lines observed by Crew have been seen bright in the chromosphere, while those observed by Dunér have not been so recorded. Hence he concludes that the lines observed by Dunér are produced by the absorption of vapours actually lying in the interstices of the photosphere-and therefore indicating the same velocity-while those observed by Crew show only the uniform angular velocities of the ellipsoidal shells.

Many other problems are discussed, and Dr. Brester has satisfied himself that his theory is competent to explain them all. Want of space, however, will not permit further reference.

The volume will be a valuable one, if only for the fact that it brings together a great mass of work which has been done in connection with the sun-over 300 authors being quoted-and although we are not prepared to accept his theory in all its points, it is fair to say that some of his arguments are extremely suggestive, and may help in time to unravel some of the mysteries of our central luminary.

In subsequent communications Dr. Brester will extend his theory to the phenomena presented by variable stars, comets, and other celestial bodies. A. F.

[blocks in formation]

Changes in the Spectra of Sun-spots. Dr. Brester's TH

theory also gives an explanation of differences in the spectra of sun-spots at different parts of the spot-period. Observations have shown that at maximum the lines which are most widened in spot-spectra are chiefly lines of unknown substances, while at minimum they are chiefly lines of iron and other known substances. When it is remembered that there is a progression in latitude with the advance of the spot-period, Dr. Brester's view can readily be understood; the photosphere in each latitude will have a different composition, and hence change of

HIS book deals with certain of the types of animals and plants which are included in other elementary works on the same subject. The forms selected are yeast, protococcus, bacteria, mucor, penicillium, chara, fern, flowering plant, amoeba, vorticella, paramœcium, hydra, mussel, crayfish, and frog. The author states that "the subjects dealt with cover most elementary biological courses, but apparently do not exactly fit any." The work has, therefore, at any rate, the merit of not having been written merely from the point of view of any particular examination syllabus. A certain amount of originality

is also seen in the attempt to combine a more general treatment of the subject with practical directions.

General instructions with regard to the microscope, microtome, and reagents, are given in the introduction; these, however, do not indicate a very wide personal acquaintance with the ordinary laboratory requirements, and the methods of preparation, &c., are mainly copied from Lloyd Morgan's "Animal Biology" and Howes's "Atlas of Practical Elementary Biology." The student is referred to a number of well-known text-books for further information, but it is curious that no mention is made of certain excellent elementary works treating more especially of the types described.

The part dealing with plants, which occupies rather more than half the book, is on the whole more satisfactory and contains fewer mistakes than that relating to animals. Most of the woodcuts in the former are taken from well-known sources, and a number of original figures are given of Aspidium and of Lamium album, which latter is selected as a type of the Phanerogams; the author has evidently worked out the structure of these forms with some care. In the zoological part many of Lloyd Morgan's diagrams have been utilised, and figures are also taken from various other text-books, such as Milnes Marshall's "Frog," Wiedersheim's "Comparative Anatomy," and Quain's " Anatomy." Most of those from the last-named work, with the corresponding descriptions, naturally do not refer to the frog at all, but this fact is not stated. Some of the drawings of invertebrates made by the author are very fair, though they do not indicate much originality; one or two others, such as that of an undischarged nematocyst of hydra, on p. 221, are bad. The sources from which borrowed figures are taken is not mentioned in all cases, although the contrary is stated in the preface.

The author shows very little power of selecting his facts, or of drawing conclusions from them in such a way as to clearly illustrate the general principles of the subject. Many of the details, moreover, are incorrect, and errors of the most serious character occur. It will be sufficient

to refer to a few of these in order to indicate the author's looseness of expression and want of acquaintance of parts of the subject with which he deals.

The remarks on the structure and functions of the nucleus, and on the pulsating vacuole in protococcus (pp. 46 and 47) are, to say the least, misleading. This organism may, it is said, " be looked upon as a closed bag with a double wall-the outer of cellulose, and the inner of protoplasm" (p. 50), and the movements of its cilia "probably" drive it through the water (p. 48). The investment of the "spermocarp" of chara is called a "pericarp," and the pro-embryo a "prothallium" (pp. 88 and 89). The description of karyokinesis (p. 108) does not show much knowledge of recent observations. On p. 90, line 10 from top, the word "sexual" has by an oversight been printed as several." The oosphere is confused with the fertilized ovum on p. 133, although the term oosperm is correctly used on previous and subsequent pages. The description of the part played by the nucleus in the processes of reproduction and conjugation in vorticella on pp. 211 and 212 is somewhat incomprehensible. One gathers on pp. 220 and 221 that it is comparatively easy to distinguish the nerve cells in

hydra in preparations simply traced up in water and stained with methyl-blue, and in optical sections of the entire animal prepared with osmic acid. We may mention that it has recently been shown by Albert Lang that the bud in hydra is not "a product of both ectoderm and endoderm as stated on p. 223. The Metazoa are said to be all "characterized by . . . the possession of a digestive cavity (enteron)" (p. 224). On p. 234 we read that the "kidneys (nephridia)" of the mussel are "sacculated organs whose walls carry a mass of tubules," and one gathers that the small irregular opening leading from the kidneys into the "ureter" is quite easy to recognise. Fig. 194A, representing the brain of the frog, is taken from the old figure by Ecker, in which the "olfactory lobes " are separated by a cleft, and the primary fore-brain is said to be the same thing as the thalamencephalon (p. 333). We do not see the object of introducing a description of the complicated human auditory apparatus in the chapter on the frog. The account of the processes of maturation, fertilization, and segmentation of the ovum of the frog is extremely incomplete and inaccurate, and one might even infer from one sentence on p. 331 that the nucleus was quiescent during the division of the egg! We are told that the ectodermic invaginations which give rise to the "nares" become "continuous with the mesenteron" (p. 335). The description of the development of the lungs (p. 334), together with the figure copied from Wiedersheim, refer to the inammal, and not to the frog. In the account of the development of the bodycavity (p. 335), it is said that the latter, "extended upwards through the lateral mesoblastic plates, nearly meets in the middle line beneath the notochord, and so pinches the alimentary canal with its glands into the body cavity"; and on page 333 it is stated that the notochord "pierces the mesoblast and divides it into right and left halves." The numbering of the five aortic arches given in Fig. 225, and that of the three mentioned in the text is incorrect (p. 336). We learn that metamorphosis begins soon after the development of the gills (p. 336). The account of the development of the urinogenital ducts on p. 338 is quite incorrect as applied to the frog. In Chapter XVIII. one gathers that the processes of digestion in all the Coelomata are quite similar to those which occur in the higher forms, which are then briefly described.

Even if we accept the author's dictum that "he will know a good deal of botany who knows Chara and Lamium thoroughly," and give him full credit for having worked up some parts of the subject practically, we must remind him that a wider knowledge than this implies is advisable before attempting to write a book on general biology. After reading the preface and introduction, one is led to expect that the high ideal set up by the author as regards actual personal observation would at any rate have led him to examine carefully and accurately all the types described; it is very disappointing to find that this has not been the case. In conclusion we venture to repeat Darwin's advice as quoted on p. 200 of this book: Give full play to your imagination, but rigidly check it by testing each notion experimentally." W. N. P.


V'AN'T HOFF'S "STEREOCHEMISTRY." Stéréochimie. Nouvelle Edition de "Dix Années dans l'Histoire d'une Théorie." Par J.-H. van't Hoff. Rédigée par W. Meyerhoffer. (Paris: Georges Carré, 1892.)


HE second edition of this work was very fully reviewed in these columns in 1887 (vol. xxxvii. p. 121), and we will therefore content ourselves with noticing briefly the new matter contained in the present edition. We must, however, premise that the stereochemistry of the carbon compounds is based on the assumption that the four monad atoms or groups satisfying the four affinities of a carbon atom are situated at the solid angles of a tetrahedron, the centre of which is occupied by the carbon atom itself, and on the allied conception of the “asymmetric” carbon atom-" asymmetry" arising when the four attached atoms or groups are dissimilar, in which case two enantiomorphic arrangements are possible for any given set of four such atoms or groups (see the notice already referred to). In the first French edition, which bore the title "La Chimie dans l'Espace," the author discussed the greatly increased possibilities of isomerism to which this new theory led. Since then chemists have used the theory as a guide in the search for cases of isomerism, and numerous new isomeric compounds have been discovered, the existence of which could not have been predicted as long as the old constitutional formula written in one plane were employed. The history of this branch of organic chemistry has, during the past seven or eight years, been one continuous triumph for the theory. One of the most striking proofs of the value of these stereochemical views is to be found in Emil Fischer's well-known researches on the sugar group. In the group of the glucoses of the aldehydealcohol type, for example, the presence of four asymmetric carbon atoms has to be assumed, and the theory | predicts the existence of no fewer than sixteen isomerides with a normal carbon chain, as compared with the one form admissible under the older view. Several of the predicted forms have been prepared, and the relative distribution of the positive and negative asymmetric carbon atoms within the molecule has been determined by E. Fischer. This and other work confirmatory of the theory, is described and discussed in the present volume.

The theory of the asymmetric carbon atom owes its origin to the difficulty of otherwise explaining the optical rotatory power of various organic compounds. Quite recently, P. A. Guye has suggested that the numerical value of this optical rotatory power is dependent upon the relative masses of the substituting atoms or groups attached to the asymmetric carbon atom, and that if two of the four different substituting radicles are of equal mass the rotatory power will cease. He was unable to verify this view in all strictness, since, in the cases of this kind which he studied, such as that of methyl-ethylaldehyde (CH) (CH2) CH (COH), in which C2H2 = COH =29, there was optical activity. The probable explanation is, that, as suggested by Guye, not only the masses of the groups, but also the interatomic distances, of which the atomic volume is a measure, come into play here. However, by varying the weight of a given group

attached to an asymmetric carbon atom-thus, by sub stituting successively different homologous radicles-g was found possible to produce a concomitant variation z the rotatory power of the compound, to make it increase or decrease at will, and even to change its sign. Th variation is shown in ascending the series of the esters of tartaric acid and its di-acetyl and di-benzoyl deriva tives. But whereas the weight of the alkyl-group in the esters determines the amount of the rotatory power, no such influence can be perceived in the case of the metallic salts of tartaric acid, all of which display in solution the same rotatory power, irrespective of the atomic weight of the metal. The clue to this anomaly is furnished by the electrolytic dissociation theory of Arrhenius, according to which the dissolved salts are present in the form of their dissociated ions, so that, in the case of the dissolved metallic tartrates, it is the ion CO2(CH.OH)CO, which is alone responsible for the rotation. Arrhenius's theory thus receives striking confirmation from an unexpected quarter.

The subject of compounds containing closed chains as fully discussed in the present edition, and the “cis" and "trans" isomerism discovered by von Baeyer is described.

The relative position of the substituting groups in the stereo-isomerides is also discussed.

The concluding chapter deals with the stereochemistry of nitrogen-a question which had not emerged when the previous edition was published. Some of the information given under this heading is rather meagre; but doubtless the omissions are intentional and they are largely com pensated for by a very complete bibliography of the subject.

The work is in every sense authoritative, and we cordially recommend it to all interested in the most recent developments of organic chemistry. F. R. J.

OUR BOOK shelf.

Die Fossile Flora der Hottinger Breccie. By R. von Wettstein. With 7 plates. (Vienna: Imperial Printing Office, 1892.)

THE Höttinger Breccia is a formation about 50 feet thick in the neighbourhood of Innsbruck, and situated about 1200 metres above sea-level. The upper part consists of about 35 feet of coarse conglomerate, with fossils chiefly confined to a bed some 3 feet thick, while the remainder is occupied by alternating beds a foot or two in thickness of white or reddish sandstones and breccias, which are for the most part very fossiliferous. It has been well known to collectors of fossil plants for upwards of thirty years, and though at first regarded as of tertiary age, is now uniformly recognised as quarternary, possibly inter-glacial, or more probably post-glacial. The lower part is characterised by the occurrence of many berbaceous plants, such as the violet, strawberry, coltsfoot, Prunella, &c., which are replaced above to some extent by Cornus sanguinea, Rhamnus Frangula, an alder, willow, &c., indicating, perhaps, a change in the forest growth without necessarily implying any considerable interval of time. The flora is almost wholly of existing species, and in the main does not differ essentially from that which might be found in a similar situation at the present day; but six of the species no longer flourish at such an altitude, and a few others, like the box, are absent in Northern Tyrol,

while there are also indications in the relative sizes of the leaves of others that the climate was milder. Perhaps the Alps were less elevated and the sea nearer at the time, but interest is given to the problem by the undoubted presence of Rhododendron ponticum, which at present only flourishes in a much warmer climate far to the east, but, from its discovery in other localities, was evidently thoroughly indigenous in the Alps. The author regards the flora as a relic of the" steppe-flora" which then spread over the greater part of Europe, and of which numerous traces still exist, especially in Switzerland and Lower Austria, where plants of Oriental facies, such as the yew, box, holly, Ephedra, Sumach, hornbeam, feather-grass, maidenhair, &c., are its lingering remains.

The work is carefully prepared, doubtful determinations, except in the case of the Arbutus and a new buckthorn allied to Rhamnus latifolia of the Canaries, are eschewed, and the photographic illustrations, pencilled over by the artist, are extremely satisfactory. J. S. G.

but their definitions will be found in the appendix; we are afraid, however, that the suggestion that their values for certain angles should be committed to memory is not a wise one. G. A. B.


[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.]

The Glacier Theory of Alpine Lakes. THE letter of the Duke of Argyll against the theory of the of misconception of the theory itself, and so completely ignores formation of alpine lakes by glacial action shows such an amount the great weight of evidence in its favour, that a few words on the other side seem desirable.

The Duke says that glaciers "do not dig out," do not "act

Observational Astronomy. By Arthur Mee, F.R.A.S. like a ploughshare," but, when moving down a slight incline do (Cardiff: Daniel Owen and Co., 1893.)

THIS Small book should serve the purpose for which it is issued; the object being to provide the beginner with an inexpensive treatise to enable him to become familiar with and interested in the practice of observational astronomy. For this reason the author limits himself to the purely descriptive side of astronomy, dealing with the sun, planets, comets, and meteors, giving numerous references where necessary. Short chapters are given on eclipses, transits, occultations, and "the sidereal firmament," the latter treating of double and coloured stars, &c. The chapter on the telescope contains many practical hints, besides numerous woodcuts, while that devoted to the moon is very pleasant reading, and gives a good account of the more general features. The illustrations, as will be gathered from the above, are very numerous, many of them being from the pen of the author himself. With respect to these, we must add that the one given on p. 72 of the Orion nebula does not remind us of the most beautiful

object in the heavens, while on p. 66 Donati's comet is depicted minus the two long streamers which made this object so striking. The book concludes with a short obituary of the Rev. T. W. Webb and an appendix containing brief contributions from Denning on comets and meteors, Gore on variable and temporary stars, Seabroke on double star measurement, and a few others.

W. J. L. Mechanics and Hydrostatics for Beginners. By S. L. Loney, M.A. (Cambridge University Press, 1893.) THIS is the latest addition to the series of elementary text-books recently launched by Mr. Loney. The same high standard of excellence is maintained, and the author must again be congratulated on his efforts to place in the hands of a beginner a book which will give him correct ideas of the laws and principles which are included in a study of mechanics.

It consists of three parts, statics, dynamics, and hydrostatics, each part containing the usual chapters. If the reader should fail to understand the chapter on the laws of motion, he must attribute it either to his want of ability or the nature of the subject, for we fail to see how the author could improve his remarks on this part of the subject. We are glad to observe that the words "rate of change" find their way into the statement of the second law, for its definiteness is increased thereby. More than the usual care appears to have been devoted to the selection of suitable examples; some of them are exceptionally good, and thus add to the usefulness of the book. Occasionally the trigonometrical ratios are used,

[ocr errors]
[ocr errors]

scoop," as well as rub down and abrade. No observer of glaciers has ever stated, so far as I know, that they do "dig out," and it is equally erroneous to say that they scoop," for that implies that it is the end of the glacier that acts. But the end is its weakest point, where it is melting above and below, and where consequently it can do practically nothing. The whole action of a glacier is a grinding action, and its grinding power is greatest where it is thickest, and where, consequently, it presses on the rocks with the greatest weight. The result of ing glaciers; while the well-known "till" is the product of the this grinding is seen in the muddy stream issuing from all existrock grinding mill of ancient glaciers and ice-sheets.

Notwithstanding the Duke's disbelief in ice-sheets I venture to think that their former existence has been demonstrated both in Scotland and Ireland; but leaving this point, I wish to make a few remarks on the extreme inadequacy of the earth-movement theory to account for the facts. In the first place it is certain that no alpine lake can possibly have a long life, geologically speaking. In the course of a few thousands of years, certainly in less than a hundred thousand, all alpine lakes would be filled up by the sediment brought into them. It follows that all the existing lakes must have been formed about the same period, and that, geologically, a very recent one, and corresponding approximately with that of the well-known glacial epoch. But if these lakes were all formed by earth movements, either just before the glacial epoch came on, or during its continuance, or afterwards we have to explain the remarkable fact that such movements only occurred within the limits of glaciation, never beyond those limits. In Wales, Cumberland, and Scotland, in the Alps, ¦ in Scandinavia, in Finland, in the northern United States and | Canada, in Mongolia and Thibet, in Tasmania and New Zealand, we have thousands of rock-basin lakes, amid palpable signs of glaciation. But the moment we pass beyond the glaciated districts, mountain lakes abruptly cease. There are hardly any in Spain, none in the Great Atlas, none in Sardinia or southern Italy, except in the volcanic areas and away from the mountains, none in any of the West Indian islands with their fine mountain-ranges, none in the peninsula of India or in Brazil. And there is exactly the same distribution of fiords. We have them in Norway, in West Scotland, in Alaska, in South-West America, and in New Zealand, all characterised by deeper water within than at their outlets, and all in glaciated countries, but nowhere else in the world.

Now it is simply impossible to believe that at a very recent period there should have been earth-movements of such a character as to produce lakes, but always in glaciated districts and never beyond them, unless the movements were a result of the glaciation. This has not, I believe, been yet suggested; but, in view of the modern theory that any considerable loading of the surface produces subsidence, it is at least a possible explanation. But there are some important facts that seem more in favour of the grinding out of the lake-basins by the enormous weight of ice accumulated over their sites during the height of the ice-age. Looking at a geological map of the Alps it will be seen that most of the lakes are more or less bordered by tertiary or secondary rocks. Lakes Annecy and Bourget are in miocene

and eocene; the lake of Geneva on the north side is miocene or jurassic; the lake of Neuchatel, miocene; lakes Thun and Brienz, eocene or jurassic; lake Lucerne, eocene and miocene; lakes Zug and Zurich in miocene; lake Constance miocene; lake Maggiore is mostly in gneiss, but it is very suggestive that it is here comparatively shallow, but becomes suddenly deeper and reaches its maximum depth in its lower portion where it is bordered on the east by the jurassic beds; lake Como also has its greatest depth in triassic rocks, the upper portion, where gneiss prevails, deepening gradually southward as in a submerged valley. Equally suggestive is the fact that in the eastern Alps of Tyrol and Carinthia, where gneiss, porphyry, and the older stratified rocks prevail, and where glaciers are not now so extensive, there are hardly any lakes, except on the northern borders, where a considerable number occur in eocene, cretaceous, jurassic, or triassic formations.

These various facts as to the distribution of alpine lakestheir almost total absence in all parts of the world outside of glaciated districts, and within glaciated districts their prevalence in the newer and more easily denuded rocks-are what have to be explained by the advocates of the theory of earth-movements, and this, so far as I am aware, they have never attempted to do. Equally important, and equally difficult to explain on the earthmovement theory, is the fact that alpine lakes are almost always situated just at those spots where, by means of converging valleys, the glaciers would become heaped up and attain their maximum thickness, or where there is good evidence that they have been very thick; and it is the grinding power of this enormous weight of ice, acting differentially as regards the softer and harder rocks, that has worn out hollows in pre-existing valleys now occupied by lakes. In almost every case, too, it will be seen that there is a constriction or narrowing of the valley towards or beyond the lower end of the lake, which, by preventing the free escape of the ice, has increased its thickness and grinding power.

In the presence of such important series of facts as those here referred to, mere opinions, or even small and detailed cases of difficulty, can have no weight; but there is yet another consideration, which most geologists will admit is antagonistic to the earth-movement theory. The whole tendency of geological observation is in favour of the usually very slow rate of earthmovements, while it is equally in favour of the comparatively rapid action of denudation by running water. But in order that earth-movement could form a lake, it would be necessary that the rate of elevation or depression should be so great that the river could not keep pace with it by cutting down its channel; and, considering that all the rivers in question are rapid mountain streams carrying great quantities of sediment, this will be admitted to be a very improbable supposition. But when we add to this the still greater improbability that such rapid earth movements have occurred in scores and hundreds of cases, all at about the same time, geologically speaking, and all just in those spots where it can be shown that during the glacial period ice must have accumulated, and where the rocks were of such a character as to admit of being ground away; and yet further, that no similar earth movements producing similar results have recently occurred in any part of the globe beyond the limits of glaciation, the whole assumption becomes so hugely improbable as to render the theory of lake-formation by ice-grinding easy in comparison.

Sir Charles Lyell considered that the gravest objection to the glacial erosion theory was the entire absence of lakes where they ought apparently to exist; and he instanced the valley of Aosta and the Dora Baltea, the glacier of which produced the enormous moraines of Ivrea. The valley of the Rhone above Martigny may be adduced as another example of the absence of lakes where they might be expected. But this kind of difficulty will apply to many other valleys, and can only be answered by general considerations. In both these cases the valleys are comparatively broad and open, and have a rather rapid descent. It is probable, therefore, that the ancient glacier in both was of a nearly uniform thickness, so that its wearing action on the floor of the valley would be tolerably uniform. To produce a lake we require essentially a differential action. There must be much more rapid degradation in one part than in another, due either to greater ice-accumulation or to softer rocks in one part than in another. In both the valleys referred to there is much uniformity in the rock-formations throughout, and even if some Jakes or chains of lakes had been formed, the enormous amount

of debris still brought down may well have filled up and a gether obliterated them. The absence of lakes in certain vala cannot be considered an argument of any value unt ascertained by borings that none have been formed and filled again. It must also be shown that the whole conditions in such as to produce that amount of differential grinding do without which no lake can be expected to have been formed

It certainly seems to me that all the facts, all the probabili all the converging lines of evidence, are in favour of the ga theory, to which the only serious objection is the assum that glaciers cannot move uphill. But that they can do so, have done so, is now admitted by most students of glaz motion. Mr. Jamieson, and other Scotch geologists, proved that glaciers, over 2000 feet thick, have travelled lateral valleys, and up the slopes of many hills and mountains and when we consider that the Rhone glacier was 5000 thick just above the lake of Geneva, and more than 2000 f thick where it abutted against the Jura, we can have no di in admitting that it might have travelled up the very ge slope of the lake bottom, which appears to be less than 10 in a mile in its steepest parts. ALFRED R. WALLACE

Waves as a Motive Power. HAVING frequently observed the swimming motions of fishes in our Aquarium-and occasionally of porpoises is". open sea-I have tried to make use for propelling boats ti same principle of locomotion, as exemplified particularly i tail-fin.

I fixed a fin (blade) of elastic material like a heim to the of a canoe; moving that fin laterally to and fro, the same forwards. I have since learned that this "motor" w or already twenty-five to thirty years ago by Ciotti, a Sicilian: of course only an exact version of the method of scaling one oar, familiar to all boatmen. Whilst trying my ca models of boats I soon became convinced that a boat ong move forward if elastic fins are fixed to it, directed backw in such a manner that their flat sides are pressed the surrounding water, when the boat rolls and pitches elastic fins, whilst overcoming the resistance of the w curve like the fins of a fish, driving the water backward consequently pushing the boat forwards.

The canoe was provided with two horizontal fins at the and two vertical ones at the keel, total surface 02 55 metres; speed against rather sharp wind and waves estin at 25 metres per minute. I was unable to take exact meas ments, as the canoe was accidentally sunk before the exper was complete.

I then provided another boat, three metres long, at ea the two pointed ends with a horizontal fin (later on and at the keel with two vertical fins; these were all m steel sheet, I-0.8 mm. thick, subsequently replaced aluminium bronze. The boat covered, against a gentle se wind, the distance of 900 metres in 25 minutes. Part fins obliquely the boat turned towards the right or left; one group of the fins forward, and another of equal backward, their action was paralysed, and in similar it was easy to make the boat turn round on the spot or to backward.

The changing of the surface of the fins (03 to 05 metres) caused very little difference in the speed p The same movements of the boat take place if the rou caused artificially.

I undertook a series of trials, in which I wish to ackno with thanks the kind assistance of Mr. Nelson Foley. T result was that the rolling yields so little power, energy being sufficient to prevent rolling,) that the vertica as a source of power may be nearly neglected in the


As to pitching, the power resulting from the acti waves against gravity is proportioned to (weight of heal crew) x (number of undulations) x (height of waves). Bac small portion of the energy developed in moving the and down acts upon the fins (surface of boat in water t square metres, surface of fins o'3 to 0'6 square metres this remaining available force a considerable portion> the low efficiency of the fins. Supposing, for the sake (4 ment, the efficiency to be 25 per cent., the propelling in a moderate sea works out to the fraction of a man' Considering these circumstances it seems doubtful,

« AnteriorContinuar »