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I AM very grateful to Mr. Sterland for asking for further information “on some points of difficulty” in my recent paper on Cuckows' Eggs, because it shows me where I have failed in making myself plainly understood. In endeavouring to reply so far as lies in me to his questions, I will take them in order.

THIS is the first fasciculus of a series intended to illustrate the palaeontology of Switzerland: The work is intended chiefly as a means of making known by descriptions and drawings a number of interesting fossils from the animal and vegetable kingdom, in part at least new to science. Most of these have been derived from the Swiss Alps, and are now preserved in the Bern Museum of Natural History. It is also intended to serve as the organ for shorter palasontological communications from the whole extent of Swiss territory, the several authors being answerable for their own views. The first part contains a short paper, just completed, “On the Red Limestone of Wimmis and its Fauna;” the next will contain plates and descriptions of various remarkable fossils from the Swiss Alps. Three, or at most four such parts will form a volume, when a title-page and index will be issued.

THE Zeitschrift fúr Chémie(No. i) contains an account of some unfinished experiments by Muck on manganous sulphide, and a note by Dr. Baumhauer, of Bonn, on the action óf aqueous hydric chloride on nitrobenzol. In the latter of these the author points out the interesting fact that dichloraniline is a principal product of the reaction. Robert Otto communicates several papers containing the results of experiments which he has performed, for the most part, with the co-operation of Eugen Dreher. The subjects of the papers áre “Mercuric Diphenyl,” under which title a tolerably exhaustive account of this body is given; “Mercuric Ditolyl,” which was not so extensively examined; “On the deportment of Dibenzyl at a high temperature” (it splits into Toluol and Toluylene); “On the transformation of hydro-phenylic sulphide into phenylic sulphide” (the mercuric derivative decomposes thus at 180°:— (C6H5)2HgS2= (C6H5)2,S2+ Hg); “On mercuric dinaphtyl,” from which it appears that the presence of ethylic acetate is very advantageous in the usual mixture whereby the body is prepared; “On mono-ethylic and mono-methylic mercuric acetate;” and “On the preparation of organic sulphur-compounds by means of sodic hyposulphite.”—A. Geuther contributes a short article “On the volatile acids of croton oil.” He finds that the oil contains no crotonic acid, which name is consequently a misnomer. Of the two metamers, C4H6O2, he consequently designates the solid modification tetranylic, and the liquid varie/y quartenylic acid. Croton oil contains á metamer of angelic acid, for which the author proposes the name tiglink acid. —Markownikoff finds that the butylic (fermentation) alcohol, when transformed into iodide, and then, by alcoholic potash, into olefiant, furnishes with hydric iodide the tertiary pseudo-butylic iodide. —Petrieff describes solid azoxytoluide (fusing at 57°).

MR. PROCTOR'S interesting paper in your last number reminded me of an essay on “The Nebular Hypothesis,” originally published in 1858, and re-published, along with others, in a volume in 1863 (“Essays : Scientific, Political, and Speculative.” Second Series), in which I had occasion to discuss the question he raises. In that essay I ventured to call in question the inference drawn from the revelations of Lord Rosse's telescope, that nebulæ are remote sidereal systems—an inference at that time generally accepted in the scientific world. On referring back to this essay, I find that, besides sundry of the reasons enumerated by Mr. Proctor for rejecting this inference, I have pointed out one which he has omitted.

IT is hardly possible to exaggerate the importance of the question now under discussion in NATURE, “What was Kant's view of Space ?” A mistake there is simply fatal. I therefore rejoice to find the columns of that paper are so generously thrown open to those who, like myself, are not primarily concerned with physical science. But this question, like all others in philosophy, has a proclivity to indefinite expansion, and unless its discussion be rigidly restricted to the main issue involved in it, the conductors of NATURE will have to ostracise it. Their space is not an infinite form, but a quantum to be carefully economised. It is, for example, an unwarrantable waste of that commodity to make Hegel the exponent of Kant on a point where Hegel taught that Kant was wrong.

WITH reference to an abstract of a paper by Mr. Southwell on the flight of birds, which appeared in your paper a few weeks back, I venture to make the following note and inquiry.

I FIND in your number of January 13 an interesting paper by Mr. Barrett on the Correlation of Colour and Sound. It seems to me that Mr. Barrett depreciates the phenomenon of Newton's rings by saying that the “connection between the relative spaces occupied by each colour and the relative vibrations of the notes of the scale” … “cannot be more than a coincidence.” The diameters of the rings are functions of the wave-lengths and, therefore, expressions of a physical condition. Mr. Barrett's own process is, to say the least, very rough and, after taking “the mean of two limits,” rather wide apart for the length of the waves of each colour, he obtains a series of numbers which differ not inconsiderably from those which belong to the musical scale aud he is obliged, after all, to place blue and indigo together, taking their “mean rates” as corresponding with G. I do not know how far Newton's measurements are correct; but I find that Professor Zannotti, of Naples, gives for the diameters of the rings from red to red the cube-roots of the numbers. The intervals between these, taken successively, are that is—major-tone, semi-tone, minor-tone, major-tone, minor-tone, ½tone, major-tone. Calling the major-tone M, the minor tone m, and the semi-tone x, for the sake of brevity. I will give the five different forms of which the musical scale is capable—expressed by the succession of intervals—and show that the above series of intervals is one of them. Varieties depending upon the permutation of the quantities M, m, and x. The 1st contains the imperfect fifth, DA; the 2nd two such fifths, EB and FC; the 3rd GD; the 4th A2E2; and the 5th the imperfect fifth, C2G,—all of course with their corresponding augmented fourths.

IT is not often that Faraday committed an oversight; but such I think he must have done in his well-known paper concerning the existence of a limit to vaporisation. (“Experimental Researches in Chemistry and Physics,” p. 119.*) Faraday showed experimentally, that mercury emitted no appreciable vapour below 20° F. and accounted for this on the ground that “the elastic force of any vapour which the mercury could have produced at that temperature, was less than the force of gravity upon it and that, consequently, the mercury was then perfectly fixed.” He adds, “I think we can hardly doubt that such is the case, at common temperatures, with respect to silver and with all bodies which bear a high temperature without appreciable loss by volatilisation, as platina, gold, iron, nickel, silica, alumina, charcoal, &c, and that, consequently, at common temperatures, no portion of vapour rises from these bodies or surrounds them.”

IN reply to J. H.'s query respecting the flight of the albatross mentioned in a paper of mine on the flight of birds, read at the November meeting of the Norfolk and Norwich Naturalists' Society, I beg to assure him that no bird is able to fly without flapping its wings.

YOUR correspondent G.H. will find in one of Thomson's papers something very like the assertion “that there was a time when the earth rotated too swiftly for the existence of life,” but expressed in a manner at once more precise and less pleonastic. “The existence of life” reminds me of a phrase which I heard a few days ago from a female beggar; she lamented that her husband had “fallen into habits that are habitual.” Well; the required reference is the paper “On Geological Time,” in the Transactions of the Geological Society of Glasgow, vol. iii. Part I. pp. 15 and 16 (§§ 19 and 20). A thousand million years ago, says Thomson, “there must have been more centrifugal force at the equator due to rotation than now, in the proportion of 64 to 49…. If the earth rotated seventeen times faster, bodies would fly off at the equator…. If you go back ten thousand million years ago—which, I believe, will not satisfy some geologists—the earth must have been rotating more than twice as fast as at present—and if it had been solid then [which he thinks improbable], it must be now something totally different from what it was.” Such a state of things he seems to consider inconsistent with any organic life such as we know of. Surely the connection of this question with the argument from retardation by tidal friction is too plain to need exposition.

I WISH it were possible to induce our learned societies to be a little more liberal; it should be their aim to spread knowledge, not make it a luxury for the wealthy. I happen to wish to read a paper by Professor Tait on “Rotation,” published in the Transactions of the Royal Society of Edinburgh. The only libraries I have access to are those of the British Museum and London Institution. At the Museum there is no volume of the “Transactions” later than 1864; at the London Institution no volume later than 1862; so that if I persevere in my intention of reading the paper, I must buy the volume containing it, for which I must pay 2l. 2s.—that is, I must buy thirteen papers I don't want in order to be able to read one which I do want: these include one on the temperature of newly-born children, and another on tetanus in cold-blooded animals.

“THE first four books of Euclid : or the principal properties of triangles, and of squares and other parallelograms treated geometrically : the principal properties of the circle and its inscribed and circumscribed figures treated geometrically.” Such is the wording of the programme put forth by the University of London, of the Mathematical portion of the examination for matriculation candidates. Whether the papers have ever been drawn up in accordance with it I cannot say, but certainly my experience for the last four or five years has led me to believe that the alternative side has, of late, at least, been altogether ignored.

ON the 5th of March died at Vienna Joseph Redtenbacher, Professor of Chemistry at the University. He was born in 1810, and studied under Eichig, conjointly with whom he published a determination of the atomic weight of carbon, and several other memoirs. His principal merit consists in the discovery of acrolein and acrylic acid. Most of his papers were published between 1839 and 1848. With his death chemistry in Austria passes entirely into younger hands; his colleague, Professor Schröber, the discoverer of amorphous phosphorus, having lately been nominated Master of the Mint, and replaced in his chair by Illasiwetz. The succession of Redtenbacher will be divided into two parts, and the building of a new laboratory on the largest scale will open a vast field to the activity of his successors.

IN the course of a re-perusal of Helmholtz's “Ton-empfindungen,” it occurred to me to compare the theory of consonance and dissonance, there propounded, with the exposition of that theory presented in the Lectures on Sound of Professor Tyndall. The result of the comparison is the present paper, in which I shall endeavour to show that Professor Tyndall's version of the theory is radically different from the original, and erroneous.

I SHALL feel obliged if, through the medium of your widely-circulated journal, you will allow me to point out an extraordinary mistake into which Mr. Radau has fallen, in a memoir inserted in the Annales Scientifiques de l' Ecole Normale Supéreure tom. vi. 1869, in which he criticises certain of my conclusions about the representation of the motion of a free rotating body contained in a paper published by me in the “Philosophical Transactions” for 1866. In his preamble, M. Radau says, speaking of the theory of rotation in connection with the names of Poinsot, Rueb, Jacobi, and Richelot:—“Tout récemment M. Sylvester a essayé d'appliquer au mêne sujet des considérations nouvelles qui l'ont conduite à des résultats intéressants, à côté d'autres dont l'exactitude peut être contesteé.”

IN the tenth number of the Comptes Rendusfor the present year, is a paper by M. Pouch et, on the Modifications of the Nests constructed by the common Swallow, (Hirundo urbicaLinnæus,) in which he remarks that it is evident the mode of life of certain animals, far from being persistent and invariable, undergoes modifications under different terrestrial conditions, and that, in many instances, their habits are different from what they were in former ages. Spallanzani indeed remarks in one of his remarkable memoirs on the swallows, that the shape and structure of the nests of birds are interesting features in their history, and that each species constructs its habitation on a plan peculiar to itself, which never changes, and is continued from one generation to another. And this opinion is shared by many naturalists; observations, however, when sufficiently close and attentively made, show that it is erroneous. We do not indeed see any modifications of those of their habits which are associated with their biology, so that the arboreal species seek to form for themselves a subterranean nest, or rear their young ones in dwellings adherent to the coigns of our houses, but it nevertheless is ascertained that in a succession of years, each learns to improve the construction of his residence. Certain birds work up only the products of our own handiwork, and would necessarily employ natural substances if these were deficient. Thus, as may be seen in the museum of Rouen, the Loriot of Europe sometimes forms its nest with thread ends under the branches of trees, which cannot possibly be the natural method. For several centuries the common swallow has disported itself in our crowded cities, and with its friendly masonry attached itself to our houses. The chimney swallow, still more familiar and audacious, often builds in the smoky shafts of our domiciles, or even in the noisiest factories, undisturbed by the din or the fires or the movement around them. Such habits must form a strong contrast with those of their predecessors in times long gone by. When we ourselves wandered untutored savages in the prehistoric times, or when still later we constructed lacustrine towns, or megalithic monuments, the habits of the birds can scarcely have been identical with those of to-day, for such human edifices afforded little security or shade. They must then have built amongst rocks. Nearly the same remarks apply to the storks, which have not remained stationary, but have preferred to their less commodious dwellings those offered to them by man. These changes in the industry or the manners of birds are perhaps even more rapid than we might at first sight suppose; and M. Pouchet's observations have demonstrated to him that notable improvements have been adopted by swallows in their modification during the first half of the present century. Having directed a number to be collected for the purpose of having drawings made from them, M. Pouchet was astonished to find that they did not resemble those he had collected some forty years ago, and which were still preserved in the museum of Rouen. The present generation of swallows have notably improved on the architecture of their forefathers, amongst those still building in the arches and against the pillars of the churches. Some, however, still adhere to the old methods, or such nests may possibly have been old ones which have undergone reconstruction. In the streets, on the other hand, all the nests appeared to be constructed on the new method. And now for the differences observed. The old nests show, and all ancient writers as Vieillot, Montbrillard, Rennie, Deglaud, &c., describe the nest of the house-swallow as globular, or as forming a segment of a spheroid with a very small rounded opening, scarcely permitting the ingress and egress of the couple that inhabit it. The new nests, on the contrary, have the form of the quarter of a hollow semi-oval (le quart d'un demi-ovoide creux), with very elongated poles, and the three sectional surfaces of which adhere to the walls of edifices throughout their whole extent, with the exception of the upper one, where the orifice of the nest is situated; and this is no longer a round hole, but a very long transverse fissure formed below by an excavation of the border of the section, and above by the wall of the building to which the nest is attached. This opening has a length of nine or ten centimetres and a height of two centims. M. Pouchet considers this new form affords more room for the inmates and especially for the young which are not so crowded, whilst they can put out their heads for a mouthful of fresh air, and their presence does not interfere with the entrance and exit of the parents. Lastly, the new form protects the inhabitants of the nest better than the old one, from rain, cold, and foreign enemies.

THOUGH the spectra of different salts of bases which show well-marked absorption bands often differ in detail, yet they generally resemble one another so much that there is no difficulty in recognising each element. Judging from facts hitherto known, it was more probable that spectra of the new type described in my former paper*were due to a new element than that they were merely due to a combination of zirconium with uranium, and that there seemed to be no reason for suspecting a few special compounds of uranium would give spectra with bands unlike all others. Uranic salts, when in a state of moderately fine powder, give a spectrum not only showing absorption-bands, but also those which depend on fluorescence, and are characteristic of light reflected from the powder.† These two kinds of bands can be easily distinguished by means of a plate of deep blue cobalt glass, which proves that the abnormal bands seen in the spectra of the compounds of zirconia with the oxides of uranium are due to genuine absorption and not to fluorescence.

WE have referred in another column to Lieut.-Colonel Strange's valuable paper, read before the Society of Arts. The following is a report of the more important part of it. After giving a sketch of the history of the movement in favour of a recognition by the Government, of the necessity of defining the relations which should subsist between the State and scientific education throughout the country, commencing with the meeting of the British Association at Norwich in 1868, Colonel Strange proceeds to state the points which he thinks should be especially kept in view in the proposed inquiry. These are:—

THE Student and Intellectual Observer, New Serie, No. 2, for April, contains an article entitled “Animals as Fellow-Boarders,” being a translation of Von Beneden's valuable paper on Commensalisme, read before the Belgian Academy, describing the habits of creatures who may be said to board together, but whose association is distinct from that of victim and parasite. They are of two kinds, Free Fellow-Boarders, such as the tiny pea-crab, which lives in mussel-shells; and the Fixed Fellow-Boarders, like the barnacles which cover the skin of whales.

IN the paper on this subject by P. L. S., there occurs a remark which is calculated to convey a mistaken impression. He states that “an Antarctic station is only required for the transit of 1882, and there is ample time to make a preparatory Antarctic expedition to ascertain” whether a suitable station can be found. The reverse is the case. No Antarctic expedition can be of any service in 1882, so that in a preparatory expedition the lives of our seamen and men of science would be uselessly risked. On the contrary, there are several Antarctic stations suitable for observing the transit of 1874; and I have shown that the comparison of observations made at such stations with observations made in Siberia would give the most effective means of determining the sun's distance available before the 21st century.

I OBSERVE in your interesting paper of Feb. 17th, a statement that the larger varieties of Dinornis had, in all probability, become extinct before the occupation of the Middle Island of New Zealand by the present race of natives. I have observed previous statements to the same effect, supported by the authority of gentlemen whose opinions deserve the highest consideration, and by the assertion that no tradition of the existence of such birds has been found amongst the present representatives of the native race. I have good reason to question the accuracy of the latter assertion, at any rate.

THE May number of the Journal of Botany, British and Foreign, commences with the first part of a Clavis Agaricinorumby the well-known fungologist, Mr. Worthington Smith. The general classification of the Agarics adopted by Fries and Berkeley is followed; but several new sub-genera are proposed. An ingenious tabular view accompanies the paper, presenting the salient features of the series and sub-genera of this vast genus at a glance. Dr. Seemann continues his revision of the natural order Bignoniaceœ; while the Hon. J. L. Warren contributes a paper on a sub-division of Rubus, a most intricate genus, to which he has paid special attention; and Dr. H. Trimen a description of a new British Callitriche. Other short notes and notices fill up the number, which maintains the interest for British botanists especially, promised on the commencement of the new series.

IN an interesting paper, quoted at p. 661 of NATURE, Prof. Rolleston dwells upon the proportion of short-lived male skeletons, found in Anglo-Saxon interments, as contrasted with the older character of the Romano-British interments, deducing therefrom a conclusion as to their respective longevity. The writer appears to have forgotten that the youth of Romano-Britain had for many generations been forcibly expatriated—drafted abroad to feed the armies of Imperial Rome.

IN the last number of NATURE you give an abstract of a paper by M. Duchemin on the destruction of carp by toads. The fact that carp are so destroyed is, or was, well known. Walton, in his “Complete Angler,” says:—“And I have known of one (person) that has almost watched the pond, and at the fishing of the pond, found of seventy or eighty large carps not above five or six; and that he had foreborne longer to fish the said pond, but that he saw on a hot day in summer, a large carp swim near the top of the water with a frog upon his head; and that he, upon that occasion, caused his pond to be let dry; and I say, of seventy or eighty carps, only found five or six in the said pond, and those very sick and lean, and with every one a frog sticking so fast on the head of the said carps, that the frog would not be got oft without extreme force or killing.” Walton also mentions that pike are attacked and destroyed in the same manner. Walton wrote his “Complete Angler, or Contemplative Man's Recreation” in 1653. The confusion between frogs and toads was one likely to be made at a time when natural history was so little studied. In all other respects Walton's account agrees with M. Duchemin's.

Journal of the Chemical Society, April 1870. This number contains a “Note on some Reactions of Alcohols,” by Mr. E. T. Chapman. The author finds that on distilling with caustic soda a mixture of the rotating and non-rotating amylic alcohols to dryness, the distillate contains a larger proportion of the rotating alcohol than the original liquid; and, on adding water to the residue of sodic amylate and distilling the alcohol which passes over with the water is almost free from the rotating variety. A repetition of the process renders it quite pure. He also finds that repeated treatment of the rotating alcohol by caustic soda converts it into the non-rotating. On treating amylic alcohol to which about 2 ¼ per cent, of water was added with a quantity of sodium just sufficient to decompose the water, and distilling, water first passed over, followed by amylic alcohol; sodic amylate almost free from caustic soda remaining in the retort; showing that the sodium replaces the hydrogen of the alcohol in preference to that of the water. Again, on distilling a solution of caustic soda in amylic alcohol, water passed over with the alcohol, the residue being sodic amylate.—“Note on the Organic Matter contained in Air,” by Mr. E. T. Chapman. Several methods were tried for collecting the organic matter from the air before estimating its quantity. Passing the air through water in a Liebig's potash apparatus, or even in a tube with twenty-five bulbs, did not fix the whole of the organic matters. Cotton wool and gun-cotton failed on account of their invariably containing nitrogenous bodies, which vitiated the results; the condensation of steam in the air and washing with fine spray were better, but not satisfactory. Filtering the air through asbestos paper succeeded very well, but the asbestos was difficult to manage. The process finally adopted was to pass 100 litres of air through a quantity of finely powdered and moistened pumice stone, placed on a piece of wire gauze, fixed on the wide end of a funnel; distilling the pumice with dilute potassic hydrate and potassic permanganate, and determining the quantity of ammonia in the distillate by Nessler's test. In crowded rooms and near an untrapped sink, the air was found to contain organic bases as well as ammonia. 100 litres of air from crowded rooms contained quantities of nitrogenous substances, producing from 0˙02 to 0˙35 milligrammes of ammonia.—Then follows a lecture by Dr. Gladstone on “Refraction equivalents,” which has already been noticed in these columns. The number concludes with a long paper by Dr. Thudichum on “Kryptophanic acid, the normal free acid of Human Urine.” From the analysis of the salts it appears to be a dibasic acid of the formula C5H9N O5or a tetrabasic acid containing C10H18N2O10

DR. INGLEBY is curious to know what Prof. Helmholtz would say on this vexed question. If Dr. Ingleby will turn to page 630 of the “Physiologische Optik,” he will find that Prof. Helmholtz has anticipated his wishes. As others of your readers may be interested in seeing how the matter is treated by one who is facile princeps in this department, I subjoin a translation of the passage. If the curious experiment mentioned by Dr. Ingleby had referred only to the vertical diameter of the disc, it would have seemed to be another illustration of our inveterate tendency to ascribe an exaggerated value to vertical lines or angles, at or near the horizon. It is said that if ten men be required to fix off-hand on a star half way between the zenith and horizon, nine, at least, will choose one very much too low. If an exact square be cut out in paper and pinned against the wall opposite to the eye, the sides will appear longer than the top or bottom. If an equilateral triangle be placed in the same position, the angles at the base will appear larger than the angle at the vertex. If a line be drawn parallel to the bottom of a sheet of paper, and a second line, making with it an angle of 20° or 30°, any one attempting, without moving the paper, to draw a third line through the point of intersection, so as to make an angle with the second line equal to that which the second makes with the first, will make the second angle too large. (This experiment is guaranteed by Helmholtz.) After reading Helmholtz's theory, metaphysicians may be willing to allow that all these illusions are to be derived, after his example, from the clouds. As metaphysicians have, before now, contributed a good deal to the clouds, it is perhaps only fair that the clouds should contribute something to the metaphysicians.

YOUR issue of June 2 contains a long letter from “Nemo,” to which a short reply seems desirable. Most of his statements are incorrect, and, as an illustration of the trustworthiness of his facts, or supposed facts, allusion may be made to his remark that all he can find in the Cyclopædia about Arvicolœ, Crocidurœ, Crossopi, Hypudœus, and Sorices is that Hypudœus is sometimes spelt Hipudœus is sometimes spelt Hipudœus; whereas all the species mentioned in the Close Time Report to which he refers are described or noticed in the Cyclopædia. The species of the sub-genera Crocidura and Crossopus are referred to under their generic heading Sorex in the article Sorecidœ, E. C. Some of the terms which he says are omitted properly belong to another division of the Cyclopædia. Thus Acclimatisation is noticed in the Arts and Sciences division, and something additional will probably be given in the supplement to that division. Again, Deep Sea Dredging had scarcely become a subject of general interest when the Natural History Supplement was being written, while the character of the principal results, and the probability of great additions to the subject, rendered it advisable, as was thought, to postpone its consideration until the Arts and Sciences division was supplemented. Some of the results are, however, given under Alcyonaria and elsewhere in the Natural History Supplement. As regards the other subjects said to be omitted, most of them do occur. Darwinism is noticed under Species, E. C. S., and also under Palœontology, Crustacea, &c. . Dimorphism in Animals will be found under Annelida, Hydrozoa, Generations (Alternation of), Crustacea, &c., in E. C. S. Eophyton is noticed; and Eozoon is repeatedly mentioned, while its systematic position is described under Foraminifera. The article Entophyta in E. C. is devoted to the fungi connected with skin diseases, while those which are associated with ague and other diseases would be most appropriately noticed in connection with those diseases, which do not belong to the Natural History division. A whole column is given to Hyalonema under Alcvonaria, E. C. S., in which the contradictory views of Drs. Bowerbank, Gray, Wright, and others, are distinctly referred to Something is said about Hybridity under Primula. Ornithoscelida is not in; the term was first proposed in a paper read Nov. 24, 1869, which paper was not published in the printed form until after the Supplement had been finished. The general views on Protoplasm are given under Cells, Amœba, and so far as it is identical with Sarcode under Actinophrys, Sarcode, and other headings in E.C.S. Rhizocrinus is referred to under London Clay, and its occurrence in the living state mentioned. Aerolites: The latest reference is said to be 1861, implying, as it seems, that none of the information is of later date. Falls subsequent to 1861 are mentioned, and many of the facts are of later date ; as, for example, those relating to the Alais and Orgeuil aerolites ; Sorby's conclusions published in 1865 ; and Daubrée's experiments, of which accounts were given in 1866 and 1868. The article itself appeared early in 1869. As to the bibliography, the principal authors are mentioned, and a list of the works consulted was written, but was inadvertently omitted. It is also said that the latest reference under Alca is 1861, but this again is not correct. The writer of the article Annelida was not aware of Claparède's strictures at the time he wrote it; but, after all, they do not seem to affect materially the general statements given in the supplementary volume. Prof. Huxley's views respecting the systematic position of Archœopteryx are given under Birds, E.C.S. No reference is made to Protagon under Blood, E.C.S., nor is mention made of Day's colour tests, nor Dr. Richardson's renunciation. Of the last, all that was found in the Reports of the British Association is the title of his paper, which runs thus, “On Coagulation of the Blood; a correction of the Ammonia theory,” and of which nothing more is said. Hence it was thought best to say nothing about the matter. Of the long string of terms which “Nemo” has culled from Prof. Huxley's last address to the Geological Society, and which are said to be omitted, the majority are given in the Supplement. For instance, to cite one or two cases : Anthracosaurus occurs under Carboniferous system, E.C.S.; Evolution under Palœontology; Micrslestes under Rhœtic Beds; and so on. As to the other remarks which have not been specially alluded to, it may be admitted that some of the articles might have been improved. Foraminifera would have been all the better if Haeckel's volume had been consulted, only Haeckel's work could not be got. It would have been very desirable if subjects which have been omitted had been inserted, and if cross references had been more numerous; but there were restrictions as to space which rendered it necessary to make a selection. Thus, Meloe was inserted and Sphegidœ rejected, because there was no room for both. What a Cyclopædia ought or ought not to contain is an open question. It cannot give information upon everything; and probably very few persons not specially interested in the subject want to know about Hyœnictis or Ictitherium. If regard was had to the theoretical view of the matter, and not to the cost and other practical drawbacks, a full, account of all that has been done in the last sixteen years would fill several volumes as large as the Supplement to the “Natural History Division of the English Cyclopædia.” I beg to sign myself

A FEW years ago I read ten or a dozen papers of a masterly history of geometry by M. Chasles. It was in French, in some quarto transactions of a learned society.

Your correspondent T. W. Webb may be glad to know that a graphic account of the Aerolite he refers to (NATURE, July 14) as having fallen in Berkshire in 1628, will be found in Vol. II. of Chambers' Papers for the People, published 1850, in an article entitled “Memorabilia of the 17th Century,” p. 10. This article also contains many other very extraordinary and well-described accounts of earthquakes, floods, mirages, and various startling atmospheric phenomena which occurred during the 17th century. Amongst the latter the accounts of parhelia, or mock suns, and haloes, and the falls of two or three aerolites, are worth noticing.

WE have received from Archdeacon Pratt a copy of a paper communicated to the Philosophical Magazineon Delaunay's objection to Hopkins's method of determining the thickness of the earth's crust by the precession and nutation of the earth's axis.

THE Geological Magazinefor July (No. 73) contains rather ewer original articles than usual, but what there are will be found interesting. The series of notices of eminent living geologists is continued in a notice of one of the most accomplished of the number, Professor John Phillips, of whom we have a good biography, but a very unsatisfactory portrait. Mr. Carruthers gives a notice of the so-called fossil forest near Cairo; he distinguishes a new species of Nicolia(N. owenii), and illustrates its microscopic structure as compared with that of the old species N. ægyptiacaUnger.— Mr. Kinahan communicates a paper containing a comparison of the geological features of Devon, Cornwall, and Galway, with a discussion of the means by which they have been produced; and Miss E. Hodgson a long disquisition on the origin and distribution of the granite-drift of the Furness district. The longest article in the journal is a report of Mr. David Forbes' lecture on Volcanoes, which will be read with much interest.

IN reply to Dr. Ingleby's note I may state that many papers by M. Chasles on various subjects in the history of Mathematics, are to be found in the volumes of the Comptes Rendus for 1837, onwards. His “Aperçu Historique” &c., originally appeared as a special volume of the Transactions of the Brussels Academy, but was sold as an independent work. It appeared in quarto, and was published in 1837. Like his “Traité de Géométrie Supérieure,” it is very rare, and fetches an enormous price. Mr. Quaritch is, perhaps, the most likely bookseller in London to be able to procure it. The German translation by Sohncke is comparatively cheap, and may be readily obtained through Messrs. Williams and Norgate.

IN the report of the papers read at the Academy of Sciences, Paris, June 13, which appears in NATURE for June 30, it is stated that MM. Jamin and Amaury presented a note on the above subject, in which they point out, apparently as if it were something new, that the specific heat of some of these mixtures rises even above that of water.

IN reference to the production of ozone it may interest your readers to know that the quantity developed here has been unusually great during the last few days. On Sunday evening, during the electrical agitation that occurred and ended in a slight discharge, accompanied by heavy rain, we had the highest reading. Mr. Burrows' test paper registered 9, and was almost black. This observation was taken at 10 A.M. During the period of this development the air was very moist. Last evening and this morning have caused the ozonometer to register 7, and this is above the average. To-day, Tuesday, the hygrometer indicated the point of saturation. I may add that old Gilbert White's remark as to activity of swifts during thundery weather has been greatly confirmed. They have kept up an almost incessant screaming during the last few days.

AT the present time when we are, as it were, taking stock of our Scientific Institutions, an account of the various schools and colleges in the United States, in which Science is made a chief, if not thechief subject, may be welcome to our readers. A paper in the Canadian Naturalist, by Prof. Dawson—the result of the Professor's travels through the States, in order to determine by personal visits the practical working of the American Science Schools, and to use the experience so obtained, in the founding of a Canadian School of Science at Montreal—has been largely used.

AT page So of my “Revival of Philosophy at Cambridge,” I ventured to describe a question set by Mr. Mahaffy, at Trinity College, Dublin, as “very oddly worded.” I might have said very improperly worded, and have justified the sentence; but for the fact that it was the Cambridge examination-papers only that were the subject of my criticism in that work. My boldness in this censure on Mr. Mahaffy has occasioned remark. That gentleman is confessedly a capital metaphysician, perhaps of greater power than the learned professor whose work he translated and annotated. I therefore ask for space in NATURE to assign the reasons on which I asserted that his question was “very oddly worded.” Here is the question: “Explain the statement that his [Kant's] doctrine of Space and Time is based on a transcendental distinction.” I think I cannot be in error in taking this as a reference to the Kritik der reinen Vernunft, Transac. Æsth. § 8, Allgemeine Anmerkungen, &c., and in particular to the paragraph beginning “Die Leibnitz-Wolfische Philosophic,” &c., and that which immediately follows. In the former, and indeed in its immediate precursor, Kant is impugning the view that affection and function (Sense and Intellect) have only a logical difference, as if Sense were only differenced from Understanding by the inferiority of its representations, in precision and clearness. The latter paragraph (the third of those I have referred to) beginning “Wir unterschieden sonst wohl unter Erscheinungen das,” &c., may be thus rendered:—

THE appearances presented by the transmission of polarised light through crystals, have long been known as the most magnificent in Optics. It is our intention in this paper to give an account of the more recent observations which have been made respecting the phenomena exhibited by uniaxal crystals, accompanied by such an explanation as will, we hope, render them intelligible to persons very slightly acquainted with science. We shall therefore avoid as much as we can the use of technical terms, and assume as little as possible to be previously known to the reader.

THE greater part of the Revue des Cours Scientifiquesfor July 23, is occupied by the commencement of a very able paper read before the Anthropological Society of Paris by Prof. Broca, on the Transformation of Species. Commencing with the pre-Darwinian theories of transformation of Blainville and Lamarck, he then proceeds to give a résuméof the theory of Darwin, and the arguments in favour of or against the permanence of species, drawn from the observation of living species and from palæontology. Following this we have, à proposof the war, an article on field ambulances and hospitals, by Prof. Champouillon. In the number for July 30, we have the rectorial address of von Littrow to the University of Vienna, on the backward state of science among the ancients, and the conclusion of M. Broca's paper on the transformation of species, in which the subject is treated from a philosophical point of view, and the professor sums up strongly against the idea of permanence. The hypothesis of Natural Selection is then discussed, but a much less certain conclusion arrived at. The number for August 6 opens with a report of the discussion on the nomination of Mr. Darwin as corresponding member of the Academy of Sciences, to which we have referred in another column. This is followed by a singularly able and exhaustive review by M. Claparède, of Geneva, of Mr. A. R. Wallace's Essays on Natural Selection, in which he points out that while Mr. Wallace demands the intervention of a superior force to explain the foundation of the human races, and to guide man in the path of civilisation, he altogether denies the existence of such a force as assisting to produce the inferior races of animals and plants, which he attributes entirely to the operation of Natural Selection. In the same remarkably interesting number of the Revue, we have also Mr. Marey's extremely important paper on the Flight of Birds.

ON my safe delivery, after a good deal of labour, from the perils of war, and on my arrival in London from Germany, I found your letter, enclosing a copy of Dr. J. Barker's communication as printed in your issue of the 14th ult. Dr. Barker has, apparently, no fault to find with my report, which, as a matter of necessity, could not be otherwise than imperfect. But he somewhat loftily criticises the writer of the comments on my report, who, in spite of the facetious title given to him by Dr. Barker, I believe to be a gentleman of considerable merit, and one whose comments on my correspondence appear to be always most just. Dr. Barker is right when he states that the late Earl of Derby's father did not observe the facts about the Kangaroo which he records; these were observed by the keeper of his collection, but they were placed on record by the Earl and hence the mistake. Dr. Barker seems annoyed that he should be made to appear as if he adopted the views, the absolute nonsense, of the writer whose paper he permitted to be read. Those who know Dr. Barker know what absolute nonsense it would be to believe him capable of adopting them. Yet, ought he not, as chairman, to have repudiated and refuted them? Would it not have been well if he had given the members of the learned societies, on the occasion in question, the information which he now offers to the readers of NATURE, and instead of telling them “that the actual passage of the fœtal kangaroo from the uterus to the pouch was not yet proved,” he had told them that the fact of there being such an actual passage had long since been proved; though how the actual transit, whether with the help of the mother's paws or lips, takes place, is still regarded as a matter for further observation; and so, instead of appearing to justify the reading of such a paper as the one referred to, he would from the extent of his knowledge on the subject, have reflected credit on his position, and on the societies to which he belongs, and have made, at least, an effort to advance the science he is so zealous for.

YOUR article entitled “Water Analysis” consists of a review of a book, a commentary on a paper, and the reviewer's opinions of the character of Mr. Chapman and myself.

THE theory has long been prevalent among practical agriculturists that the proximity of berberry trees produces rust in wheat. Men of science, unable to trace herein the sequence of cause and effect, long derided the idea, and placed it among the prejudices of the agricultural mind. The facts of the farmer have, however, been too strong for the science of the botanist, and experience has won the day over theory. Let us trace for a moment the history of the inquiry. The first reference to the injurious influence of the berberry on corn appears in Krünitz's Encyclopædia, published in 1774. Marshall, in 1781, speaks of the berberry having been extirpated in Norfolk for this reason, and Schöpf, in 1788, mentions the same idea as prevalent in New England. Other writers of the same period give similar testimony; and in 1806 Sir Joseph Banks writes thus in the Annals of Botany:—“It has long been admitted by farmers, though scarcely credited by botanists, that wheat in the neighbourhood of a berberry bush seldom escapes the blight. The village of Rollesby, in Norfolk, where berberries abound, and wheat seldom succeeds, is called by the opprobrious appellation of ‘Mildew-Rollesby.’ Some observing men have lately attributed this very perplexing effect to the farina (pollen) of the flowers of the berberry, which is in truth yellow, resembling in some degree the appearance of the rust, or what is presumed to be the blight in its early state. It is, however, notorious to all botanical observers that the leaves of the berberry are very subject to the attacks of a yellow parasitic fungus, larger, but otherwise much resembling the rust in corn. Is it not more than possible that the parasitic fungus of the berberry and that of wheat are of the same species, and that the seed is transferred from the berberry to the corn?” The acute suggestion thrown out by Sir Joseph Banks, at a time when so little was accurately known of the structure of fungi, was not followed out for half a century; it was reserved for the German fungologist, De Bary, within the last few years to establish the truth of his theory, and to prove the existence of the phenomenon of Alternation of Generation among Fungi. The researches of Steenstrup and others have made us familiar with this remarkable phenomenon among the lower forms of animal life, but had hardly prepared us to meet with it in the vegetable kingdom. It appears probable, however, that the phenomenon is by no means uncommon here also,—affording another instance of the law that it is in their lowest forms that the animal and vegetable kingdoms approach one another most nearly,—and that whole tribes of fungi hitherto considered distinct are but different phases of one another. This remark applies especially to the two genera of minute parasitic fungi, Æcidiumand Puccinia, to which the rusts in question belong, both belonging to the family Uredineœ. The well-known orange-red spots so common on the leaves of the berberry are produced by the Æcidium berberidis, while the rust of wheat and other cereal crops, but found equally on some other species of grass, as the common couch-grass or Triticum repens, is the Puccinia graminis. In the volume for 1865 of the Monatsberichte der kön. preuss. Akademie der Wissenschaften zu Berlinis a paper by Dr. De Bary, giving an elaborate account of his experiments on the propagation of these two fungi, in which, if his experiments are reliable, he clearly proves the correctness of Sir Joseph Banks's suggestion that they are one and the same species. The experiment was tried, with due precautions, of inoculating the leaves of the berberry with the spores of the Puccinia, the result being the production, not of the same fungus, but of the Æcidium, while the sowing of the spores of this latter fungus on the leaves of couch or wheat produced conversely the Puccinia. By sowing the spores of either fungus on the plant on which it was itself parasitic, he failed altogether to reproduce the same plant; and this alternation of generation may serve to account for the fact which has often been noticed, that rust is apt to appear not in successive but in alternate years on the same crop.

I. —A VERY COSTLY AND VEXATIOUS FALLACY

THE degree of rapidity with which an explosive substance undergoes metamorphosis, as also the nature and results of that metamorphosis, are, in the greater number of instances, susceptible of several modifications by variations of the circumstances under which the conditions essential to chemical change are fulfilled. Gun-cotton furnishes an excellent illustration of the manner in which such modifications may be brought about. If a loose tuft or large mass of gun-cotton-wool be inflamed in open air by contact with, or proximity to, some source of heat, the temperature of which is about 135°C. or upwards, it flashes into flame with a rapidity which appears almost instantaneous, the change being attended by a dull explosion, and resulting in the formation of vapours and gaseous products, of which nitrogen-oxides form important constituents. If the gun-cotton be in the form of yarn, thread, woven fabric, or paper, the rapidity of its inflammation in open air is reduced in proportion to the compactness of structure or arrangement of the twisted, woven, or pulped material; and if it be converted by pressure into compact masses, solid throughout, the rate of its combustion will be still further reduced. If to a limited surface of gun-cotton, when in the form of a fine thread or of a compactly pressed mass, a source of heat is applied, the temperature of which is sufficiently high to establish the metamorphosis of the substance but not adequate to inflame the products of that change (carbonic oxide, hydrogen, &c.), the rate of burning is so greatly reduced that the gun-cotton may be said to smoulder without flame; the reason being that the products of change, which consist of gases and vapours, continue, as they escape into air, to abstract the heat developed by the burning gun-cotton so rapidly that it cannot accumulate to an extent sufficient to develop the usual combustion, with flame, of the material. For similar reasons, if gun-cotton be kindled in a rarefied atmosphere, the change developed will be slow and imperfect in proportion to the degree of rarefaction, so that, even if an incandescent wire be applied, in a highly rarefied atmosphere, to the gun-cotton, it can only be made to undergo the smouldering combustion, until the pressure is sufficiently increased by the accumulating gases to reduce very greatly the rate of abstraction, by these, of the heat necessary tor the rapid combustion or explosion of the substance. If, on the contrary, the escape of the gases from burning gun-cotton be retarded, as by enclosing it in an envelope or bag of paper, or in a vessel of which the opening is loosely closed, the escape of heat is impeded until the gases developed can exert sufficient pressure to pass away freely by bursting open the envelope or aperture, and the result of the more or less brief confinement of the gases is a more rapid or violent explosion, and consequently more perfect metamorphosis of the gun-cotton. So, within obvious limits, the explosion of gun-cotton by the application of flame or any highly heated body is more perfect in proportion to the amount of resistance offered in the first instance to the escape of the gases; in other words, in proportion as the strength of the receptacle enclosing the gun-cotton, and the consequent initial pressure developed by the explosion, is increased. Hence, while gun-cotton has been found too rapid or violent in its explosive action when confined in guns, and has proved a most formidable agent of destruction if enclosed in metal shells or other strong receptacles, it has hitherto been found comparatively harmless as an explosive agent if inflamed in open air or only confined in weak receptacles. Modifications, apparently slight, of the manner in which the source of heat is applied to explosive agents, when exposed to air under circumstances in other respects uniform, suffice to modify the character of their explosions in a remarkable manner. Thus a modification of the position in which the source of heat is placed with reference to the body of a charge of gunpowder, which is only partially confined, suffices to alter altogether the character of the explosion produced.