volume shows that the last hundred pages include the more important part, we will first deal with chapters v. to viii. Beginning with a sketch of the dependence of man on his environment, the author proceeds to an account of the effect of environment on the development of various races. To the English reader one of the most interesting parts of chapter v. will be the account of the effect of the isolation and other physical peculiarities of Britain on the development of the English race.

In chapter vi. the author more especially deals with the dependence of the native races of North America on geographical and climatic conditions. This section leads by a natural transition to the competition between the white colonists and the Indians, and to the effect of barriers and strongholds in retarding or helping the gradual spread of the white races in North America.

Chapter vii. deals mainly with the relation of man to soils and climate, with the introduction of the negro race, and with the extent to which the negro and the white races are likely to compete.

In chapter viii., Prof. Shaler turns to the sparsely inhabited regions west of the Mississippi, and here he treats mainly of the capabilities for settlement of tracts still untried by white men. He speaks of the climatic conditions, of the probable value of the soils, of the reclamation of the arid regions by irrigation, and of the probable fitness of the Western States for permanent settlement by men of Aryan race he concludes that this part of America is capable of sustaining an enormous population, and that white men can thrive in most parts of it.

To those who have not read Prof. Shaler's articles in Scribner's Magazine, we can recommend the last four chapters of his book as giving an interesting and readable account of man's relation to Nature in North America. The first four chapters we cannot praise they seem to be largely made up of miscellaneous notes hastily put together with little arrangement and without careful revision; they swell the bulk of the volume, but bear only remotely on the relation between Nature and man in North America.

Chapter i. treats mainly of the zoological and botanical provinces of the present day, and their dependence on physical barriers and on climate. These pages are full of interspersed suggestions as to what might have been if conditions had been different, but some of these suggestions do not seem to have been carefully thought out, and sometimes the author adopts irreconcilable views in other parts of the same volume. We find, for instance, numerous speculations as to the effect that would be produced by the diversion of the Gulf Stream, and, among others, the following passage, in which, after speaking of the lowering of the initial velocity that would follow from a submergence of the peninsula of Florida, the author observes (p. 21):

"It is mainly, if not altogether, to this initial velocity that we owe the efficiency of the Gulf Stream as a warmthbringing current in high latitudes."

"It is a well-known fact that our oceanic streams are, in the main at least, a consequent of the movement which the air has in the trade-winds of the tropical district."

The author apparently does not observe that if the trade-winds are the main cause of the equatorial current, it is probable that the persistent south-westerly winds of the North Atlantic may also have much to do with the ocean current which follows the same course.

In chapter ii., Prof. Shaler speaks of the nature and origin of continents, development of life, mountain growth, saltness of the sea, &c.; and in chapter iii., of the permanence of continents, including a sketch of the position of the shore-lines from pre-Cambrian times to the Glacial epoch. Chapter iv. deals with a great variety of subjects, such as the condition of the faunæ and floræ in Cambrian time, Croll's theory of the origin of coalmeasures, conditions of continental growth in Europe, uniformity in past time of the composition of the atmosphere, and variations in the Gulf Stream.

Prof. Shaler, in his first four chapters, deals so largely with questions relating to the geographical distribution of animals and plants, that it surprises us to find a good many statements which more care in revision would certainly not have allowed to pass. Thus, speaking of local forms that must be developed through the longcontinued competition of different assemblages brought into close proximity in a mountainous district, the author remarks (p. 27) that:

"In a continent such as Europe, where a great diversity in the mountain systems favours the localization of life and the development of peculiar forms, the tendency is to develop in separate mountain strongholds particular species, and evolve their militant peculiarities until the forms are fitted to enter into a larger contention with their kindred species in less localized assemblages of life."

The example is most unfortunately chosen, for of all the continents Europe least illustrates the process; one would have thought that no naturalist would have brought forward the Europe of the present day as a good illustration of the differentiation of species on mountains and in isolated valleys. Our Alpine flora and fauna, instead of varying greatly on the different chains, are more remarkable for their uniformity over all the continent. of local origin, for the Glacial epoch is of too recent a Our valleys seldom, if ever, contain plants and animals affected Europe too seriously to allow many pre-glacial date for many local forms to be developed, and has forms to survive in their original limited stations. Had Prof. Shaler pointed to the mountains of sub-tropical birds, we should not have objected. and tropical America, with their local species of hummingWe have marked many other equally questionable statements, which it is surprising to find made on the authority of Prof.

Shaler.

The occurrence of various statements of doubtful accuracy, the debatable character of much of the evidence, and the complicated nature of the questions dealt with, make us hesitate to endorse the author's opinion that this book "is particularly designed for the use of beginners in the study of geology." Speculations as to what might have been if conditions had been different are scarcely suitable for the beginner in any branch of natural science. The skilled naturalist or geologist, able to discriminate, may obtain useful hints from the present volume.

C. R.

OUR BOOK SHELF.

Stones for Building and Decoration. By George P. Merrill, Curator of Geology in the United States National Museum. (New York: John Wiley and Sons, 1891.)

THIS work deals almost exclusively with the building and ornamental stones of the North American continent, the references to similar rocks in Europe and elsewhere being usually meagre and sometimes disappointing. As an account of the rocks of the United States which are of economic importance as building materials, the work is, however, a very admirable one; and, as might have been expected in a treatise bearing the name of so well-known an authority as Mr. Merrill, the book is replete with valuable information both to the geologist and the architect.

Mr. Merrill gives, in the introduction to his work, an interesting sketch of the gradual substitution of stone for wood as a building material among the early settlers in New England, and then proceeds to sketch the distribution of the different varieties of building stones in the several States and Territories of the Union. The chapters which follow, on the minerals of building stones, and on the physical and chemical characters of the rocks which are employed in construction, are very admirably written; the illustrations of the microscopical structure of building stones, and the remarks on the nature and causes of disintegration in different varieties, being alike excellent. In classifying building materials, Mr. Merrill very wisely adopts a combination of practical and scientific methods. Among the crystalline and vitreous rocks, he distinguishes, in the first place, those which are simple or made up of one mineral only-namely, steatite and soapstone, serpentine (including the verdantique marbles), gypsum (including alabaster and satin spar), and limestones with dolomites. In dealing with the compound rocks, or those built up of several different minerals, Mr. Merrill adopts the usual petrographical distinction of massive and schistose (or foliated) rocks. The former he divides into the four groups of rocks containing free quartz, rocks without quartz, but containing orthoclase felspar, rocks with plagioclase felspar, and rocks without felspar. The fragmental rocks are divided into the psammites (sandstones, &c.), the pelites (clays, &c.), the volcanic tuffs, and the rocks built up by organisms.

The chapters on the methods of quarrying, working, and testing building stones are especially admirable, and the illustrations of the great quarries of the United States, reproduced from photographs, are of great interest. The remarks on the processes which have been devised for the protection and preservation of building stones, and the tables giving the crushing strength, specific gravity, ratio of absorption, and chemical composition of all the chief varieties of building stone employed in the United States, cannot fail to be of great value to practical men. It would be hard to find a more admirable example of the value of exact scientific knowledge when applied to the treatment of economic questions than is afforded by the work before us.

Les Champignons. Par A. Acloque. (Paris: J. B. Baillière et Fils, 1892.)

THE author of this book has found much to interest him in the study of his subject, and he communicates in a clear, pleasant style the leading facts and laws which have been brought to light by mycologists. Having presented in an introductory chapter some general considerations, he proceeds to deal with the subject from the anatomical, the physiological, and the economical points of view. Finally he gives a summary of mycological taxonomy. The book belongs to the "Bibliothèque Scientifique Contemporaine," and is in every way worthy of a place among the other volumes of the series.

Theory of Heat. By J. Clerk Maxwell. Tenth Edition. With Corrections and Additions by Lord Rayleigh. (London: Longmans, Green, and Co., 1891.) THIS book is so well known, and has been of such good service to students, that it is scarcely necessary to do more than note the fact that a tenth edition of it has been issued. Only such corrections and additions have been introduced as seemed, in Lord Rayleigh's judgment, to be really called for. They are in great measure derived from Clerk Maxwell's later writings.

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.]

The Implications of Science.

PERMIT me, through your columns, to thank Mr. E. T. Dixon for his letter, which appeared in NATURE of December 10, 1891, p. 125, concerning my lecture on the implications of seience, and, very briefly, to reply to it.

He is very much mistaken in thinking that I place our knowledge of "the law of contradiction" and of "our own continuous existence" in the same category. I regard them as The former is an abstract truths fundamentally distinct.

principle, the latter a particular fact. Since Mr. Dixon merely

affirms without arguing, he must permit me to contradict him, and say that the law of contradiction is a necessary and objective truth-one that does not merely express a "verbal convention," and is not "of the nature of a definition." It is so objective that Omnipotence itself could not violate it-could not, e.g., cause a creature to have at the same time both four and only three legs. But our continuous existence" is so far from

being a necessary truth that, if an Omnipotent Creator exists, there can be no impossibility in our annihilation. That we cannot be annihilated while we know we are actually existing is, of course, true; but that fact, so far from serving Mr. Dixon's argument, is but an example of the validity of the law of contradiction. We cannot at the same time be both "consciously existing" and "absolutely annihilated." My critic seems to be still in bondage to that subjectivism and nominalism wherein I was so long involved, and whence I only extricated myself slowly and with much trouble.

As to memory, I said that we may, as everybody knows, make mistakes, but that nevertheless we are as certain concerning some parts of the past as of the present. Most assuredly I am quite as certain that I read Mr. Dixon's letter as that I am now in the act of replying to it. Our confidence in our memory cannot depend upon induction, because, if we had it not at starting, we could make no induction or enumeration whatever. My implications of science" are truths, and not "purely verbal assertions," but I never affirmed any "peculiar certainty for "mathematical conclusions." Helmholtz has never shown, to my knowledge, that two straight lines could ever inclose a space. Of course, if his supposed dwellers on a sphere" chose, as Mr. Dixon says, to apply that term to what are not straight lines, different conclusions would follow. No one denies that two curved lines can be conceived of as inclosing a space.

Similarly, if Mr. Dixon's inhabitants of the Dog Star chose, as he again says, "to define four as I + I + 1," then for them two and two would not be four. But who was ever so absurd as to suppose they would be? If any persons choose to give to the term "an angle" the signification we express by the words "a mutton chop," then certainly our conception of a triangle would not apply; for three such angles would not be equal to two right angles.

Mr. Dixon is good enough to instruct us that "the law of contradiction never tells us whether anything is or is not." But what man out of Bedlam would suppose that a statement of an abstract general law would inform us about a particular concrete thing? On the other hand, the law of contradiction does not tell us, and never by any possibility could tell us," that the terms 'is' and 'is not' are not applicable to the same thing"-though

by applying that abstract universal and necessary law to such things as "terms,' we see that a term applicable to anything cannot at the same time be the very opposite.

Mr. Dixon says: "If anyone chooses to say a thing both 'is' and is not,' there is no law against his doing so, only if he does so he is not talking the Queen's English." But by so doing he breaks the law of reason, if not the law of the land; and, indeed, to act on such a principle when on oath in a court of law might, after all, have inconvenient consequences.

My critic is obliging enough to say in plain and simple terms: "Dr. Mivart is wrong in speaking of the objective absolute validity of the law of contradiction." To this I might content myself by replying: "Quod gratis asseritur gratis negatur"! But let us avoid the use of the terms "is" and "is not": they are not necessary for my purpose. Does Mr. Dixon really doubt whether, if he had lost one eye, he would still remain, after that loss, in the very same condition he was in before? If anyone does not see the objective impossibility of such a thing everywhere and everywhen-i e. if he does not apprehend the application of the law of contradiction-then he either does not understand the question, or his mental condition is pathological. The implications of science are implied. Men may pretend to doubt them, their own existence, or the objectivity of mathematical truths. But their practice shows their unfailing confidence in them on each occasion as it arises-as when cheated by false accounts, personally injured, or engaged in scientific research. When we enter the laboratory, we leave these follies outside. ST. GEORGE MIVART.

Hurstcote, December 22, 1891.

WILL you allow me to say a few words in reference to four points in Mr. E. T. Dixon's indictment (NATURE, December 10, p. 125) of Mr. St. George Mivart?

(1) Mr. Dixon asserts that the law of contradiction "is not a necessary truth at all, it only expresses a verbal convention ". it "never tells us whether anything 'is' or 'is not.' It only informs us that the terms 'is' and 'is not' are not applicable to the same thing.' But though it may be only a "verbal convention" that in "the Queen's English" not is the sign of negation, it is not a mere verbal convention that if a signifies the negation of A (whatever A may stand for), then A and a "are not applicable to the same thing"- -as the law of contradiction asserts, and as Mr. Dixon himself allows. A highly abstract law that is concerned with the relations of propositions cannot, of course, tell us whether any particular thing exists or not--but then no one has ever expected that it should; and moreover, assertions (or denials) of the "existence" of particular objects are not the only "real" propositions (Mr. Dixon appears to be misled here partly by the ambiguity of is).

(2) Mr. Dixon says that the law of gravitation-like other laws suggested by particular experiences-depends ultimately upon induction fer enumerationen simplicem; that is, upon an inference of the form This A is X, that A is X, &c. (= Some A's are X),.. All A's are X (for we can make nothing better out of an induction by simple enumeration). But this inference is merely an immediate inference, and moreover an illegitimate one; hence, according to Mr. Dixon's view, inductions have no logical justification whatever.

(3) Further, Mr. Dixon asserts that "the supposed peculiar certainty of mathematical conclusions is solely due to the fact that they are truisms," or "purely verbal assertions,"-by which I understand him to mean definitions. In answer to this I should maintain that the peculiar certainty of mathematical propositions, and the fact that here, by help of a single instance, we unhesitatingly conclude to the universal, are (as I have observed elsewhere) explicable by "the consideration that we here see at once the connection, which in other cases we believe on grounds very different from a perception of self-evident interdependence of attributes. When the equality of the interior angles of any one triangle to two right angles has been demonstrated to us, we infer without a moment's doubt that the same relation of equality may be asserted of the interior angles of every triangle; and this because we have seen that with the attributes signified by the interior angles of a triangle' there is bound up the attribute of being equal to two right angles.' We believe that, if a certain amount of arsenic has on some occasions produced death, it will always produce death, on the ground that the apparent likenesses are connected with unapparent likenesses; but we have not seen in this case (as we have in the case of the triangle) that there is a self-evident

interdependence. And here we see why it is that, in the case of mathematical inductions, we do not need to use Mill's 'Inductive Methods.""

(4) When Mr. Dixon goes on to say that, "if the inhabitants of the Dog Star defined 'twice,'' two,' and four' as we do, then 'twice two' would be to them four'; but to say that it was so could only give verbal information," he may be refuted out of his own mouth. For he goes on to remark that, "if the people in the Dog Star chose to define four as 1+1+1, the socalled necessary truth' would not even be true!"; thus showing clearly that it is the facts signified, and not the words which signify them, that we are concerned with. According to Mr. Dixon, it would be (for me) a necessary truth that I have a headache, or am writing with a lead-pencil; while mathematical truths, in as far as "real," are obtained by induction, and are therefore not necessary. I hold, on the contrary, that mathematical truths, though obtained by induction, are necessary that is, true under all circumstances-and that it is only by a confusion between "necessary" and "certain" that a statement of the apprehension of present fact can be called a "necessary truth." E. E. C. JONES. Cambridge, December 14, 1891.

66

Deerness Public School, Kirkwall, December 28, 1891. SIR,-On reading your very interesting work on Elementary Meteorology," I find, on p. 201, reference made to "an extraordinary bow" which appeared at Kirkwall, November 13, 1871, which you explain by the reflection of the sun's rays from a water surface.

On Saturday, the 26th inst., at 3.20, when the sun was on the horizon, I saw a very distinct rainbow; there was no trace whatever of the secondary bow, but between where it ought to have been and the primary one there were several patches of what are called "supernumerary" bows. The only colour I saw distinctly was the red.

This lasted for about four minutes, when, finally, a second bow appeared just inside the primary, with the colours arranged as in the primary-not reversed, as the secondary. The space between the violet of the primary and this one was almost nil. The red next the violet of the primary was about as distinct as that of the primary. The orange and yellow were distinct also, but the others could hardly be seen. This was, no doubt, owing to the fading light of day, and to the dark colour of the clouds in the north-east, where the bows appeared. These lasted distinctly and complete for about one minute. The bows formed, as is well known, half a circle. The sun was setting behind land at the time, and the wind was blowing at the rate of forty-five miles, so that there could be no water reflection.

If I am not troubling you too much, would you kindly say if this is unusual, and if caused by the "interference" of rays? Yours respectfully,

(Signed) M. SPENCE.

Aurora Borealis.

A FINE display of aurora was observed here on the evening of January 4. A faint northern glow was seen at 8.30, which quickly grew in brightness, and at 8.45, streamers in great quantity were visible. At 9 these became tinted with glowing red on their upper portions. After exhibiting lively motions for a quarter of an hour or so, the phenomenon settled down into a brilliant and steady arch of light, red on the outside and white within, resting on what appeared to be a bank of dark cloud. By eye estimate this arch would extend about 90 along the horizon, its apex over the north-north-west from 25 to 30 in height. The glow was still visible at 10 p.m., though considerably diminished in intensity. During the whole of the day a dry and frosty north-west wind prevailed, and the temperature at 10 p.m. was 28. J. LOVEL

Driffield, East Yorkshire, January 5.

A Double Moon.

ON December 22, a well-defined double moon was seen 7m. before sunrise, which is here now at about 7. The fictitious moon was as a disk of white glass, through which the under-lapping part of the true moon could be seen. Atmospheric conditions being similar next morning, I watched for a repetition of the phenomenon, but after some abortive efforts, consisting of repeated, momentary, ill-defined projections of the moon's shape at a distance of three times the space occupied by her diameter, it was finally "given up.' ROSE MARY CRAWSHAY. Mentone, Hotel du Louvre, December 30, 1891.

ON THE RELATION OF NATURAL SCIENCE TO ART1

II.

THERE is yet another direction in which art owes instructive disclosures to the progress of photography. In the year 1836, the brothers William and Edward Weber represented, in their celebrated work on the "Mechanism of the Human Locomotive Apparatus," a person in the act of walking, in those attitudes which, according to theoretical calculation, must occur successively during one step. Thence a strange fact became apparent. At the beginning and end of each step, while the body rests for a short time on both feet, the pictures agree perfectly with the ordinary way in which painters have been accustomed to represent walking persons. But during the middle of the step, while one foot is swinging past the other, the effect is highly eccentric, not to say ludicrous; the individual appears to be stumbling over his own feet like a tipsy fiddler, and nobody had ever been seen walking in such a way. On the last page of their book, the brothers Weber propose to test the correctness of their diagrammatic figures by the aid of Stampfer and Plateau's stroboscopic disks, in the shape of Horner's Dædaleum, which has, strange to say, returned to us from America as a new invention, under the name of "zoëtrope" or even vivantoscope"; but whether the proposal was carried out or not, does not appear. However, William Weber lived to see his assertions thoroughly justified almost half a century later by instantaneous photography. It was first put into practice in 1872 by Mr. Eadweard Muybridge at the suggestion of Mr. Stanford, in order to fix the consecutive attitudes of horses in their different paces. The result was the same as in Weber's diagrammatic figures; pictures were obtained which nobody could believe to have seen in reality. On photographs of street life and processions the camera frequently surprised people in attitudes quite as odd as those attributed to them by the brothers Weber on theoretical grounds. The same is the case with the remarkable series of photographs of a flying bird during one beat of its wings, obtained by M. Marey with his photographic gun.

2

The explanation is known to be as follows: An object in motion, the speed of which varies periodically, leaves a deeper and more lasting impression on our mind in those positions which it occupies longest, while the impression is fainter and more fleeting in those through which it passes quickly. Apart from all knowledge of this law, a painter would never represent a Dutch clock in a cottage with the pendulum at the perpendicular, as every spectator would inquire why the clock had been

An Address delivered by E. du Bois-Reymond, M.D., F.R.S., at the annual meeting of the Royal Academy of Sciences of Berlin in commemoration of Leibnitz, on July 3, 1890. Translated by his daughter. This Address was first printed in the weekly reports (Sitzungsberichte) of the Berlin Academy, then in Dr. Rodenberg's Deutsche Rundschau, and lastly it was published as a separate pamphlet by Veit and Co., at Leipzig, 1891. Con tinued from p. 204.

Philosophical Magazine, January 1834, 3rd Series, vol. ii., p. 36.

stopped. The pendulum, having swung in one direction, necessarily stops for a moment while preparing to return in the other, and consequently its diverging position is more vividly stamped on our minds than those during which it passes through its position of rest with a maximum of speed. Precisely the same thing occurs with the alternately swinging legs of a man during the act of walking; the body remains longest in the position in which both feet support it, and shortest in that during which one foot swings past the other. We therefore receive scarcely any impression from the latter series of attitudes. We imagine a walking person, and painters accordingly represent him, in the interval between two steps, with both feet touching the ground.

In the case of a running horse, however, particular circumstances intervene. However rapid the succession of instantaneous photographs, we never obtain the usual image of a racing horse such as it appears in large numbers in the print-shops at the racing season, and such as we suppose we actually see in reality. It is different in the case of man; there among pictures obtained methodically or by chance, which have, so to speak, never been perceived by the naked eye, some will always occur which agree with the usual aspect of a walking person. The difference consists in this, that in a racing horse the interval of time, during which the fore-legs remain in complete extension, does not coincide with that during which the hind-legs are fully extended. Both these positions prevailing in our memory, they are subsequently blended into the traditional picture of a racehorse, whereas instantaneous photography fixes them successively. Consequently the traditional picture is wrong, and exhibits the horse in a position through which it does not even transitorily pass.

In the year 1882, an illustrated American paper brought out a picture of a steeplechase, in which all the horses are copied from Muybridge's photographs, in attitudes only visible to a rapid plate. This ingenious sketch was communicated to us by Prof. Eder in Vienna, in a pamphlet on instantaneous photography, and a stranger spectacle cannot well be imagined. The correctness of these apparently wrong pictures can, however, be proved by realizing the idea originally suggested by the brothers Weber, and integrating into a general impression the periodical motion which has been resolved, as it were, into differential pictures. This is done by gazing in the dædaleum at a series of photographs taken at sufficiently brief intervals from an object in periodical motion, or illuminating or projecting it momentarily during its rapid flight past the eye. The latter method has been put into practice by Mr. Muybridge himself in his zoopraxiscope," and with us in the electric stroboscope by Mr. Ottomar Anschütz, a most skilful handler of instantaneous photography. In both instruments we see men and horses reduced to their natural mode of walking, running, or jumping-with one exception. The speed with which the slits of the dædaleum pass before the eye, or the period during which each picture is illuminated, being exactly the same for the whole series, the general effect produced is somewhat different from what it would On the whole, however, the position in which both feet are touching the ground, prevails, because the motion of the legs slackens when approaching this position, so that the pictures follow each other more closely and almost coincide.

be in real life.

The series of instantaneous photographs taken by Mr. Muybridge and Mr. Anschütz from an athlete, during the performance of a muscular effort, are an inexhaustible source of instruction to students of the nude. Mr. Anschütz's stroboscope exhibits a stone- and a spearthrower in all the different stages of their violent action: their muscles are seen to swell and slacken, until finally the missile is represented after its discharge, as it cannot move any faster than the hand in the act of hurling it.

Animal painters will find equally useful the instantaneous photographs which Mr. Muybridge and Mr. Anschütz have obtained from domestic and wild animals.

Even on breakers in a stormy sea the camera has been employed with surprising success. In making use of these photographs, painters should, however, remember that the human eye cannot see the waves as a rapid plate does, and beware of producing a picture which in certain respects would be quite as incorrect as the clock which appears to have been stopped, or the man stumbling over his own feet.

Finally, the traditional representation of lightning in the shape of a fiery zigzag has been recently proved by Mr. Shelford Bidwell, on the evidence of two hundred instantaneous photographs, to be just as wrong as the traditional picture of a racing horse. Mr. Eric Stuart Bruce endeavours to vindicate the zigzag by taking it for a reflection on cumulus clouds; it is, however, difficult to understand how its sharp angles can be accounted for in this way.

Prof. von Brücke has devoted a special essay to the rules for the artistic rendering of motion, which, together with the laws on the combination of colours, have at all times been unconsciously followed by the great masters.

A cultivated and artistically gifted eye, supported by sufficient technical knowledge, was always able to compose genuine works of art in photography, as Mrs. Cameron long ago proved. In our days, Dr. Vianna de Lima has shown how this branch of art has been advanced and extended by instantaneous photography. It contributes a solution to Conti's question in Lessing's "Emilia Galotti "-whether Raphael, had he been born without hands, would not the less have been the greatest of painters. The photographic plate has been described as the true retina of the philosopher; and one might add, of the artist, if it were not unluckily almost colourblind. Unfortunately, theoretical reasons which experience will hardly contradict render it highly improbable that the expectations still entertained by artists and the general public, with regard to photography in natural colours, will ever be realized.

Whether photography does not act unfavourably on the reproductive arts, such as engraving, lithography, and woodcutting, by taking their place to an increasing extent, remains to be proved. Its fidelity is certainly such as, in a certain sense, to lower the value of the original drawings of old masters, by making them common property. An exhibition, arranged by one of our art-dealers several years ago, of the best engravings of the" Madonna della Sedia," together with a photograph from the original, first opened our eyes to the extent to which each master has embodied in his copy his own individual conception. But even were photography to cause such a retrogression in the reproductive arts, of what importance would that be, compared to the immeasurable services which, as a means of reproduction itself, it renders art, by disseminating the knowledge and enjoyment of artistic work of all kinds and periods? No one can fully estimate and appreciate what it has done to beautify and enrich our life, whose memory does not reach back into those, as it were, prehistoric times, "when man did not yet travel by steam, write and speak by lightning, and paint with the sunbeam."

Is it credible, after all this, that there can be any need of mentioning the benefits derived by art from the study of anatomy? Has not the "Gladiator" of the Palazzo Borghese given rise to the conjecture that there were anatomical mysteries among the Greek artists, as the only means by which they could have obtained such complete mastery of the nude? Was it not through incessant anatomical studies that Michael Angelo acquired the knowledge necessary for the unprecedented boldness of his attitudes and foreshortenings, which are still a 1 NATURE, vol. xlii. pp. 151 and 197.

source of admiration to anatomists such as Prof. Henke and Prof. von Brücke? Has not provision been made by all Governments that methodically encourage art, to afford to students an opportunity of training the eye on the dead subject to note what they will have to distinguish under the living skin? Have not three successive teachers, who afterwards became members of this Academy, been intrusted with this important duty in Berlin? Finally, do we not possess excellent compendiums of anatomy specially adapted to the use of artists?

And yet the most renowned English art critic of the day, who in his country enjoys the reputation and veneration of a Lessing, and who lays down the law with even more assurance-Mr. John Ruskin-explicitly forbids his pupils the study of anatomy in his lectures on "The Relation of Natural Science to Art,"1 given before the University of Oxford. Even in the preface he deplores its pernicious influence on Mantegna and Dürer, as contrasted with Botticelli and Holbein, who kept free from it. "The habit of contemplating the anatomical structure of the human form," he continues, "is not only a hindrance but a degradation, and has been essentially destructive to every school of art in which it has been practised." According to him, it misleads painters, as for instance Dürer, to see and represent nothing in the human face but the skull. The artist should "take every sort of view of animals, in fact, except one-the butcher's view. He is never to think of them as bones and meat."

It would be waste of time and trouble to refute this false doctrine, and to set forth what an indispensable aid anatomy gives to artists, without which they are left to grope in the dark. It is all very well to trust one's own eyes, but it is better still to know, for instance, how the male and female skeleton differ; why the kneecap follows the direction of the foot during extension, and not during flexion of the leg; why the profile of the upper arm during supination of the hand differs from that during pronation; or how the folds and wrinkles of the face correspond to the muscles beneath. Campe's facial angle, though superseded for higher purposes by Prof. Virchow's basal angle, still reveals a world of information. It is hardly conceivable how, without knowledge of the skull, a forehead can be correctly modelled, or the shape of a forehead such as that of the "Jupiter of Otricoli" or the "Hermes" be rightly understood. Of course fanciful exaggeration of anatomical forms may lead to abuse, as is frequently the case with Michael Angelo's successors; however, there is no better remedy against the Michael Angelesque manner than earnest study of the real. Finally, a superficial knowledge of comparative anatomy helps artists to avoid such errors as an illustrious master once fell into, who gave the hind-leg of a horse one joint too many; or such as amuses naturalists in the crocodile of the Fontaine Cuvier near the Jardin des Plantes, which turns its stiff neck so far back that the snout almost touches the flank.

We are, however, less surprised at Mr. Ruskin's opinions, on learning that he similarly prohibits the study of the nude. It is to be confined to those parts of the body which health, custom, and decency permit to be left uncovered, a restriction which certainly renders anatomical studies somewhat superfluous. It is satisfactory to think that decency, custom, and health allowed the ancient Greeks more liberty in this respect. Fortunately, the English department of the Berlin International Exhibition four years ago has convinced us that Mr. Ruskin's dangerous paradoxes do not yet generally prevail, and that we are free to forget them in our admiration of Mr. Alma Tadema's and Mr. Herkomer's paintings. Nor could Mr. Walter Crane's charming illustrations, the 1 "The Eagle's Nest: Ten Lectures on the Relation of Natural Science to Art," 1887.