every day, nay, every hour; that certain kinds of coaldust were perhaps less inflammable than others, and so on. Comparatively few have had the advantage of carefully studying the coal-dust flame as well as the opportunity of investigating the minutest details of a series of great colliery explosions in the mines, immediately after their occurrence. The foregoing arguments are therefore perhaps to some extent excusable; but they are none the less the outcome of the imagination of their authors. They are being pressed more and more feebly as time goes on, and they are likely, we think, before many years have passed, to vanish as absolutely as the so-called "outburst of gas" theory which for more than a generation was invariably quoted as the only possible means of accounting for the kind of explosions to which we have been drawing attention.

The late Home Secretary, Mr. Matthews, was so much impressed by the occurrence of great explosions one after the other in dry and dusty mines, that he appointed a Royal Commission on Coal-Dust in 1890. That Commission has not yet issued its report, but the volume of evidence taken before it, which has been lately published, shows to what small proportions the opposition has shrunk since the theory was first started. It is also satisfactory to observe that the number of lives lost in great explosions during the last ten years is only about one half of the number lost during the previous ten years. W. G.

REVERIES OF A NATURALIST.

Idle Days in Patagonia. By W. H. Hudson, C.M.Z.S., Author of "The Naturalist in La Plata." (London: Chapman and Hall, 1893.)

THE

HE title of this book well describes its contents; but Mr. Hudson has established so high a standard by his previous work that the present volume has something of the character of an anti-climax. In literary style, in picturesque description, and in suggestive ideas and reflections there is no falling off; but we miss the wealth of original observation and ingenious speculation which made "The Naturalist in La Plata" a masterpiece.

Mr. Hudson was wrecked on the shores of Patagonia, and had a weary tramp over the desert, of some thirty miles, to reach the settlement on the Rio Negro. There, and at some farms higher up the valley, he appears to have spent a year or more, doing nothing but wandering about on foot or on horseback, observing the habits and peculiarities of the scanty fauna and flora, noting the varied aspects of nature, and apparently thoroughly enjoying day after day of dreamy idleness. He spent some months at a house about seventy miles up the valley, which was here about five miles wide; and every morning he rode away to the terrace or plateau, covered with grey thorny scrub, and there found himself as completely alone as if he were five hundred instead of only five miles from civilisation. He says:—

"Not once, nor twice, nor thrice, but day after day I returned to this solitude, going to it in the morning as if to attend a festival, and leaving it only when hunger and thirst and the westering sun compelled me. And yet had no object in going-no motive which could be put

I

into words; for although I carried a gun, there was nothing to shoot-the shooting was all left behind in the

valley. Sometimes a dolichotis, starting up at my apthe next moment in the continuous thicket; or a covey of proach, flashed for one moment on my sight, to vanish tinamous sprang rocket-like into the air, and fled away with long wailing notes and loud whirr of wings; or, on some distant hillside a bright patch of yellow, of a deer that was watching me, appeared and remained motionless for two or three minutes. But the animals were few, and sometimes I would pass an entire day without seeing one mammal, and perhaps not more than a dozen birds of any size."

There was nothing beautiful or even pleasing to be seen

in this dreary monotonous solitude, yet he felt a great delight and satisfaction in it, which he imputes to the ancestral savage nature that still exists in all of us, though repressed and overlaid by civilisation and society.

"It was elation of this kind, the feeling experienced on going back to a mental condition we have outgrown, which I had in the Patagonian solitude; for I had undoubtedly gone back; and that state of intense watchfulness, or alertness rather, with suspension of the higher intellectual faculties, represented the mental state of the pure savage."

In the second chapter-" How I became an Idler "—we are told of a still more disagreeable adventure than the

shipwreck. Mr. Hudson was going with a friend to a

farm eighty miles up the valley. On the way they stayed a night at a deserted hut, and here he had the misfortune accidentally to discharge a revolver bullet into his knee, rendering it necessary for him to return to the settlement to be cured, perhaps to save his life. His friend tied up the wound as well as he could, and left him to get a cart from the nearest house a good distance off. He was absent a whole day, Mr. Hudson lying on his back on the ground all the time. When his companion at length returned with the cart, and lifted him up to put him into it, a large and very poisonous snake moved from under his cloak, where it had been lying close to his feet for many hours. It glided away into a hole under the wall, and Mr. Hudson rejoiced "that the secret deadly creature, after lying all night with me, warming its chilly blood with my warmth, went back unbruised to its den."

This accident kept the author for some months in bed, and for other months a convalescent unable to walk far; and thus the finest summer weather was wasted, and he acquired those habits of the country and the people that made him an idler, and prevented him from learning as much of the animal and vegetable life of the country as, under more favourable circumstances, he might have done. Yet he gives us many interesting facts and discussions, and the chapter on "The War with Nature" is one of these. This war begins when man introduces domestic cattle, cultivates the soil, and destroys the larger wild animals for food or sport. In doing this he provides food of an attractive kind for many wild creatures, and the war begins. Pumas devour his cattle; locusts destroy his grass or crops; coots, ducks, geese, or pigeons devour the grain as soon as sown, or feed upon the young shoots, or upon the ripe wheat ready for the harvest; and thus the farmer is kept in a constant state of activity and watchfulness, which really gives him a beneficial excitement in what would otherwise be a most

monotonous and unattractive existence. In one of his glowing passages Mr. Hudson thus describes and personifies the war between nature and man.

of

"He scatters the seed, and when he looks for the green heads to appear, the earth opens, and lo! an army She too, long-faced yellow grasshoppers come forth! walking invisible at his side, had scattered her miraculous seed along with his. He will not be beaten by her, he slays her striped and spotted creatures; he dries up her marshes; he consumes her forests and prairies with fire, and her wild things perish in myriads; he covers her plains with herds of cattle, and waving fields of corn, and orchards of fruit-bearing trees. She hides her bitter wrath in her heart, secretly she goes out at dawn of day and blows her trumpet on the hills summoning her innumerable children to her aid. Nor are they slow to hear. From north and south, from east and west, they come in armies of creeping things, and in clouds that darken the air. Mice and crickets swarm in the fields; a thousand insolent birds pull his scarecrows to pieces, and carry off the straw stuffing to build their nests; every green thing is devoured; the trees, stripped of their bark stand like great white skeletons in the bare desolate fields, cracked and scorched by the pitiless sun. When he is in despair deliverance comes; famine falls on the mighty host of his enemies; they devour each other and perish utterly. Still he lives to lament his loss; to strive still unsubdued and resolute. And she, too, is unsubdued; she has found a new weapon it will take him long to wrest from her hands. Out of the many little humble plants she fashions the mighty noxious weeds; they spring up in his footsteps, following him everywhere, and possess his fields like parasites, sucking up their moisture and killing their fertility. Everywhere as if by a miracle, is spread the mantle of rich, green, noisome leaves, and the corn is smothered in beautiful flowers that yield only bitter seed and poison fruit. With her beloved weeds she will wear out his spirit and break his heart; she will sit still at a distance while he grows weary of the hopeless struggle; and at last, when he is ready to faint, she will go forth once more, and blow her trumpet on the hills and call her innumerable children to fall on him and destroy him utterly."

This, the author tells us, is no fancy picture, but one painted from nature in true colours. If so it is not encouraging for emigrants; but then, the climate is superb, and it is a proverb that "once in a hundred years a man dies in Patagonia." Then, again, the bird music is unsurpassed; there are numerous exquisite songsters; and of one of them the mocking bird, he declares that the song is so varied and beautiful that all the music of our song-thrush might be taken out of it and not be much missed. Azara declared that there were as many and as good songsters in Paraguay and La Plata as in Europe, and Mr. Hudson agrees with him. The reason why Darwin and other travellers thought otherwise is, because most of the South American songsters are shy wood-birds which rarely approach man's dwellings, and are therefore only heard by those who seek them; whereas in Europe they are mostly species which haunt gardens and orchards, and cultivated fields, and are thus more or less familiar to every one. In a chapter on "Sight in Savages" it is maintained that they have no superiority in this respect to civilised man; and that what often seems like better sight is merely trained observation of objects which it is essential for them to know. There is an amusing story of a middleaged Gaucho, who laughed and jeered at an Englishman for wearing spectacles, and would not believe that bits of

glass over his eyes could possibly make him see better. The gentleman persuaded the man to try them, and they happened exactly to suit his sight, which had gradually grown imperfect without his knowing it. He stared round,

utterly amazed, and then shouted :-" Angels of heaven.

what is this I see! What makes the trees so green-they were never so green before! I can count their leaves! And the cart over there-why it is red as blood." And he went up to it to be sure it had not been fresh painted. There is also a chapter-" Concerning Eyes "-dealing with their characteristic colours, their scintillation under excitement, and the uses of these peculiarities, a subject to which Mr. Hudson has given much attention. Many old Indian burial places and village sites were found, with abundance of arrow-heads, flint knives, scrapers, mortars and pestles, stone anvils, pottery, and other objects. There were two kinds of arrow-heads, some large and very rude, others smaller and exquisitely finished, the former found mostly on the plateau, the latter in the valley. One of the village sites, where the greatest number of objects was found, had been buried seven or eight feet, and was exposed by heavy rains, which had washed away great masses of gravel and sand. Many of the smaller arrow-heads were of crystal, agate, green, yellow, or horn-coloured flint, and were perfect gems of colour and workmanship, and these were all found at one spot. Unfortunately, most of the finest specimens, which had been packed separately for security, were lost on his homeward journey-"a severe blow," Mr. Hudson says, "which hurt me more than the wound I had received on the knee."

Although this volume cannot have the same absorbing interest for the naturalist as the author's previous work, it is yet full of suggestive observations and reflections, and gives us a vivid picture of both animate and inanimate nature in one of the least known portions of the southera hemisphere. The volume is nicely got up, and is illustrated with a number of landscapes and figures of men and animals in the same style as in the author's former work. ALFRED R. WALLACE

OUR BOOK SHELF. Ueber das Verhalten des Pollens und die Befruchtungsvorgänge bei den Gymnospermen. Von Eduard Strasburger. (Jena: Gustav Fischer, 1892.) THIS forms the fourth part of Prof. Strasburger's "Histologische Beiträge," and it is largely taken up with an examination of segmentation in pollen-grains of the gymnosperms, and the contents of, and processes in, the pollen-tubes. Recent discoveries had led Strasburger to doubt the correctness of his former interpretation of the contents of the pollen-tubes, and his further researches have "confirmed in a surprising manner" the results obtained by Belajeff in his paper on Taxus baccata, entitled "Zur Lehre von den Pollenschläuchen der Gymaospermen." Strasburger is also essentially in accord with Belajeff's generalisations therefrom. Two double plates illustrate division in the pollen-grain, the develop ment of the pollen-tube, and the further processes of fer tilisation in various gymnosperms, including Tan Pinus, Ginkgo, and Welwitschia. An unusual condition is shown of cell-division in a pollen-grain of Ginke Usually two or three "prothallium cells are formed, and in part disappear before the protrusion of the pollen tube

Glaciers have, however, without doubt caused lakes in cases where they have dammed up the mouth of glens with detrital matter. The enormous masses of such matter which dam up the waters of the northern Italian lakes are most impressive. But it does not follow that the glaciers which left those great masses also scooped out the deep bed and rocky walls of the Lake of Como.

My own belief is that the great recency of large earth movements is one of the facts of geological science which has yet to be accepted; and that the slowness with which it has made progress, or has even been overborne, is entirely due to very natural preconceptions and general assumptions about the stability of the earth surfaces, such as those which find expression in Mr. Wallace's very interesting and significant ARGYLL.

paper.

Inveraray, Argyllshire, March 11.

P.S. Recent calculations in America seem to bring down the possible date of the close of the glacial epoch there to little more than 10,000 years.

The Cause of the Sexual Differences of Colour in Eclectus.

MR. F. E. BEDDARD says in his suggestive work on "Animal Coloration" (1892, p. 3) :

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"Sometimes differently coloured animals have in reality the same skin pigments. The attention of the reader will be directed in a later chapter to the remarkable difference in colour between the males and females of certain parrots. In Eclectus polychlorus this sexual dimorphism is extremely marked. It would be an exceedingly anomalous fact if the same species of bird were to possess different pigments in the two sexes; and as a matter of fact it is not so in this parrot, different in colour though the two sexes are. The same pigments are present, but the structure of the feathers is different, and thus the resulting colour as seen by the eye is different."

The last sentence (the italics are mine) is not consistent with late Dr. Krukenberg's investigations on the colours of feathers. The case is not one of structural difference in the feathers, for the differences in colour between male and female of Eclectus are occasioned by the presence or absence of the pigment itself. The green colour of the male results from a yellow pigment (psittacofulvin) lying over a blackish brown one (fuscin), but the blue colour of the female (E. linnei, auct.) simply results from the absence of the yellow pigment. The dark pigment (fuscin) is present and the incident rays of light are reflected from it, passing through a zone without pigment, which zone absorbs the rays of the red extremity of the spectrum. Here the same conditions occur which effect the blue colour of the sky. The blue is an optical colour, as is the green, but a different structure of the feathers does not come into question. The red colour both in male and female is effected by a red pigment, which is the same in both sexes, the differences in shade (as also the violet in E. grandis, e.g.) depend on the quantity of this colouring substance and in the absence or presence in different quantities of the underlying fuscin. The pigment of the yellow feathers in the female of E. grandis is the same as the yellow pigment in the green males. Dr. Krukenberg supposes that these different pigments are derived from one and the same ground substance, a supposition which appears to be very plausible.

Why the yellow pigment of the male is not developed in the blue parts of the female we do not know, nor why the different pigments in Eclectus are disposed just as they are, since we are in general quite ignorant about the causes of the disposition of colours in bird feathers; but in the case under discussion a "different structure" of the feathers would not give as sufficient an explanation of the facts as does the above. Touching the causa movens of the different colours in the sexes of Eclectus, we can only say that it is sexuality, but this, of course, is no mechanical explanation, i.e. no true explanation at all. We can only say that in most birds the male offers an overplus of colour as compared with the female, which overplus no doubt has a relation to the more vigorous biological processes or superabundant vitality in the male during certain periods, and this also holds good in Eclectus, as we see that the female wants the yellow pigment which the male possesses. But we must bear in mind that in Eclectus the young ones from the egg display already these sexual differences of colour, a fact which is as remarkable as it is rare.

MR. CUNNINGHAM'S notion as to what constitutes "a fact" would appear from his letter published in your issue of March 9 to be peculiar. It is of course only through inadvertence that he declares a mere supposition to be a fact, and states that I have "overlooked" it. His words are "he (Prof. Lankester has overlooked the fact that blind cave-animals are born or Further hatched at the present day with well developed eyes.' on he proceeds to state that no such fact is known or recorded. but that he is "quite confident" that the young of blind caveanimals have well developed eyes.

I am quite aware that an important test of the truth of my theory of the origin of blind cave-animals would be found in the details of their embryonic development, but cannot think that Mr. Cunningham is justified either in his confidence as to the result of a hitherto unattempted embryological research or in asserting what is at variance with his own subsequent avowal, viz. that there are facts ascertained as to the condition in which blind cave-animals are born, which I have ignored. E. RAY LANKESTER

Lunar "Volcanoes" and Lava Lakes.

I HAVE waited some time to see what replies might be made to Mr. J. B. Hannay's suggestion, that lunar walled plains may have been due to tides in the molten nucleus during cres formation (NATURE, vol. xlvii. p. 7).

There seem to be at least two objections to the "volcanic" theory of lunar surfacing. First, that there must have been during the earlier, and indeed later, stages of it a vast gaseous and vaporous envelope, which, as secular temperature slowly declined, would be condensed to form seas, giving rise to a long era of erosion, and extensive denudation, and formation of sedimentary strata, as on our earth. There are no traces of this or our moon, the surfacing of which is conspicuously destitute of evidences of drainage phenomena. Secondly, there is an entire absence of distinct local colour in the detail, which should be easily seen in volcanic deposits unencumbered by vegetation and weathering.

I leave it to geologists and physicists to say if they think t at all likely or possible for any globe like our moon to pass from the semi-incandescent, lava-crusted stage, with huge vaporous envelope, to the cold, airless, and waterless condition of our satellite without passing through a very prolonged era of erosion, which, as in our case, would obliterate all traces of the former era.

Judging by our vast series of stratified rocks, we are led to conclude that an exceedingly long temperate era of erosion mus in the very nature of things, supervene on the heated lava stage in all planetary development, quite obliterating the relics of the volcanic era and relaying a sedimentary surfacing.

Taking up the second objection, in re the marked absence of colour, I would point out the abnormal brightness, or ever brilliancy, of the lunar cliffs and steep inclines all over the surface It is precisely at such places that astronomers expect to see the nature of the surface and degradation due to the effect of gramtation, i.e. where (exposed to unmitigated solar heat in the day, and a cold probably below - 100° C. at night) the cliff-falls would be most frequent, and the true colour of the strata most visible

Proctor in his "Moon" (pp. 301-2) says:-" In each lunation the moon's surface undergoes changes of temperature which should suffice to disintegrate large portions of her surface, ani, with time, to crumble her loftiest mountains into shapeless heaps In the long lunar night of fourteen days a cold far exceeding the intensest ever produced in terrestrial experiments must ex over the whole unilluminated hemisphere."

Neison, on page 113 of his "Moon," also says:-"Th physical changes of various characters must be still occurring upon the moon is rendered certain by . . . the alternate heats and cooling of the lunar strata; from the nature of the expansi and contraction thus brought into play must, through numeras fractures of the resulting general disintegration, gradually m all the lunar formations." Thus "considerable changes

slowly be effected in the condition of the surface through earthfalls and land-lips' ".. "until all the more striking and abrupt irregularities have disappeared from their action."

Now it is precisely at cliff faces and steep slopes that we should best see the real colour, if any, of the superficial strata, and what do we find? Wherever we turn, from pole to pole, there is an entire absence of colour; they are white and at times as brilliant as "new fallen snow." If we scan the vast cliffs of the "Apennines," say at sunset, for hundreds of miles, rising to 8000 or 10,000 feet, with peaks up to 20,000, they are white, seen in sunshine.

If we examine the cliffs of the Sinus Iridium highlands, the huge array round Mare Crisium, or indeed anywhere else, it is the same, and without a doubt it demonstrates to us that the outer strata on the moon are of the same white material all

over the globe. Precisely where degradation is most certain, and where the true colour of the strata would be distinctly visible, there we find the most extraordinary and invariable whiteness for a thickness of at least two or three miles.

A remarkable feature of the case is that, as a rule, all cliffs are much whiter than the general surface around them. In the raised ramparts of craters and walled plains, it is well known that the outer, and more gradual slopes, are invariably darker than the steep inner cliffs facing the enclosure. In Aristarchus, Theophilus, and such like rings, at sunrise, this is very conspicuous, especially in photographs, and it is not easy to account for this peculiar feature (evidently the result of disintegration and removal of the surface by gravitation) except by the supposi tion that the outer surface all over (and excepting rays and nimbi) is snow stained by meteoric dust. "It is well known that the fall of meteoric dust on our earth is very considerable, and estimated by Dr. Kleiberg, of St. Petersburg, at about 11,435 tons per annum. It has been found on all our ocean bottoms, and on our polar snows, where it is soon overlaid or removed by winds. On the moon, however (where there is no wind and now no snowfall), it could accumulate for many thousands of years, at least on levels, and so stain them very perceptibly.'

Undoubtedly we see the true colour of the surface layers at the cliff faces, but unless the outer surface were stained in some way their bright contrast would be impossible.

Hence I take it that the outer layer of the surface all over, for at least one or two miles in thickness, is formed of snow, stained outside by a deposit of meteoric dust, the accumulation of many thousands of years, the removal of which, by gravitation, at cliffs causes their brightness, and this would explain the perennial enigma of where all the water has gone.

At low temperature neither ice nor snow vaporise, even in vacuo, and also that at low temperature ice is a non-viscous solid (like glass) has been experimentally demonstrated by Mr. T. Andrews, F. R. S., and the results laid before the Royal Society (see NATURE, vol. xlii. p. 214). The prevailing whiteness, therefore, of the lunar cliffs and steep inclines would seem to be a powerful argument against a "volcanic" surfacing to our satellite, and a good one in favour of glaciation.

The question of maximum surface temperature under fourteen days' solar heat has undergone a startling change since Lord Rosse's classical experiment. The possibility of snow existing on the moon is now admitted by leading astronomers, since the researches of Profs. S. P. Langley and F. W. Véry, of the Allegheny Observatory, have demonstrated that the maximum may be so low that the mean temperature may possibly be below - 100°C.

The old volcanic" selenology" is dying; there is no hope of any more progress in it (and that is the great sign of life in all branches of science nowadays); it is fossilised. That a "new selenology" is badly wanted is pretty obvious to all who look into the question. The surfacing of our own satellite, one of the most conspicuous and easily seen objects in the heavens, is still the standing enigma. S. E. PEAL.

Sibsagar, Asam, February 8.

when it was announced that he had agreed to deliver the Croonian Lecture, it was universally felt that it would not do to lose so good an opportunity of doing honour to an illustrious investigator. Prof. Virchow is known, of course, chiefly as a pathologist. He is the founder of the science of pathology in the sense in which it is now everywhere understood and taught; and it would be difficult to form too high an estimate of the value of this part of his labours. But Prof. Virchow is one of those men of genius who never find in any one department of research a sufficient outlet for their energies. In archæology, anthropology, and ethnology he has been for many years one of the foremost workers of the age, and he has brilliantly represented science in the political life of Prussia and the German Empire and in the municipal life of Berlin. As a teacher in the Berlin University, of which he is now Rector Magnificus, he has done much to foster a genuinely scientific spirit among the pupils who have flocked to his class-room; and as a writer he has command of so pure and attractive a style that he has been able to exercise a wholesome and stimulating influence on the intellectual life even of classes to whom science does not usually make a very strong appeal. Altogether, Prof. Virchow's career is one of which Germany has good reason to be proud. In him she possesses one of those rare and potent thinkers who touch no subject without giving it fresh significance, and who have the secret of awakening in other minds something of their own enthusiasm, independence, and vigour.

There was so great a demand for tickets that arrangements had to be made for the delivery of the Croonian Lecture in the theatre of the University of London; and here on Thursday, March 16-a crowded audience listened with the deepest interest to what Prof. Virchow had to say about the great subject in the development of which his researches have marked so splendid an era. In the evening a public dinner was given in his honour at the Hôtel Métropole. Lord Kelvin presided, while the Presidents of the Royal Colleges of Physicians and Surgeons acted as vice-chairmen. In proposing the toast of the evening, Lord Kelvin said he was one of those who had listened with rapt attention that day to the lecture delivered by Prof. Virchow. The mystery he dealt with remained a mystery, but they were conscious of no feeling of disappointment. Though it was not for any man to tell them what life was, they had been brought nearer than ever to the solution of that fascinating problem by the researches of Prof. Virchow. Mr. Huxley, Sir James Paget, and Sir Andrew Clark also spoke of Prof. Virchow's magnificent discoveries. Prof. Virchow, in responding to the toast, pressed the pleasure he felt in being welcomed by so large and so illustrious an assembly of the learned men of England." "Abroad," he said, "he had never seen anything like it." English men of science do not often indulge in demonstrations of this kind, and it is satisfactory to know that when they do try to show what they think of a great investigator their achievement does not fall short of anything done with a like intention in Paris or Berlin.

ex

This week Prof. Virchow has been in Cambridge, where he has been received with as much enthusiasm as in London. On Tuesday the University marked its sense of the importance of his labours by conferring on him the honorary degree of Doctor in Science. The following is the speech delivered by the Public Orator, Dr. | Sandys, in presenting Prof. Virchow for the degree :-Dignissime domine, domine Procancellarie, et tota Academia:

Universitatis Berolinensis Rector Magnificus, vir non modo de medicina et salute publica, sed etiam de anthropologia, de ethnologia, de archaeologia praeclare meritus, vir et sexagesimo