and Dr. Pole, it appears, wrote for him the rather jejune algebraic investigation of the principles of such machines, which, when we come to examine it, we find is merely what we may find in any elementary book on pneumatics; and owing to the omission of all the structural conditions producing loss of effect in blowing machines, exists, in fact, as a mere parade of useless symbols, of no value to the constructor or the purchaser or the user of such apparatus. Now we are wholly unable to see the necessity for thus cumbering with a needlessly hooked-on subject a book on Iron Metallurgy at all; but if otherwise, then it should have been gone into thoroughly, and in a way to be of real value to the constructor. To have done this, however, would have required some fifty pages or more, so that a far better mode, in our judgment, would have been to have simply confined the point to a reference to the great monographs which exist on this special subject, both theoretic and practical. Neither Dr. Percy nor Dr. Pole seems to have been aware of the fact that a quite exhaustive investigation of the theory of blowing machines (omitting none of the conditions of practice) and of high merit, was published as long ago as 1805, by Herr J. Baader, Counsellor of Mines of the Kingdom of Bavaria, and which was specially and by the authority of Napoleon I. translated into French and published in the Annales des Mines in 1809. There may be such a thing as apparent completeness, which yet is only the piling together of incongruity or of incompleteness.

But this want of the sense of balance and of relative importance is not confined to such collateral subjects of

practice. Dr. Percy, in the volume here noticed, devotes nine pages to the physical properties of lead, in commencing, and of these we find four (under the head of Resistance to Pressure) are occupied with details of Coriolé's fruitless attempts in 1829 to construct weighing machines, whose indications were to be derived from the compression suffered by known volumes and forms of lead pieces-a subject as indirect and foreign to the physical properties as it is far away from the metallurgy of lead.

One statement made in this part of the volume is undoubtedly incorrect, where it is said, "by hammering lead becomes harder, but acquires its original softness by annealing." The actual fact is, that lead cannot be made harder by hammering, for its annealing temperature is so low (that of every metal being a function of its fusing point), and it suffers so large a deformation by reason of its softness when hammered, that enough heat is evolved by internal work to cause the metal to anneal itself,-in other words, never to become harder. This has been fully ascertained, and the fact has even been taken practical advantage of by those engaged in "drawing lead pipe " by the older methods, who are well aware that a hard pinch at first or rapid reduction in diameter in passing through the holes of the draw-plate, heating the lead, enables it to be drawn into finished pipe with a less total expenditure of power than if drawn slowly and with so gradual a reduction in diameter as that the lead should remain always nearly cold. Were the lead hardened here by a compression quite the same in effect as hammering, the very reverse must be the case. This volume comprises a very good account of the Pattinson process for separation of silver, and also of Parkes's zinc process. What can have induced Dr. Percy (who is, we believe, fond of

scholarship) to employ such barbarous compounds as lithargefication," 'lithargefication," "desilverisation," and "decopperisation," in place of "disargentation," decuperation"? What would be thought of "desugarification" as a substitute for "desaccharisation"?-but these are matters of taste and no more.

The chapter on the ores of lead and that on the assay of lead ores are amongst the very best in the volume, which is beautifully printed with the clearest of type and paper, and with good indices. There are nine pages near the end devoted to poisoning by lead, which, though certainly not the metallurgy of lead, may prove of some use to those employing work-people in lead smelting or manufacturing operations; though we think here, perhaps, the wisest instructions might have been simply, "send the patient to the doctor." We have little confidence in amateur or improvised medicine on the part of "laymen," in such cases as lead-poisoning, at any rate. On the whole, though, as we have had to point out, this work of Dr. Percy's is not free from faults, it is, we think, in several ways the best of all those on Metallurgy which have appeared from under his pen, and in the collection and discussion of a vast array of facts is a noble volume, the very best that yet exists in English on its subject.

ance is pleasing and often beautiful, their characters are generally very clear and distinct, so that the discrimination of the species is by no means difficult, and their

PAINTED LADY (Pyrameis Cardui).

Painted Lady. Var. 1.

Natural History is easily studied; whilst the small number of the species renders it an easy matter for the beginner to procure in a season or two by far the greater proportion

of the known forms.

Although there are already many books treating specially of the British butterflies, some of them expensive, and others so cheap as to come within the reach of every one, we cannot blame Mr. Newman for adding one more to the number, especially as his work is distinguished by the great prominence given in it to the Natural History of the species. Upon this subject, as also upon the distribution of the species in Britain, Mr. Newman has long been publishing details from his own observations and those of other naturalists, in his periodicals the "Zoologist" and "Entomologist;" and the whole of the information thus accumulated is here summarised and supplemented with observations derived from other sources. Another useful feature in the present work is the insertion of notices, and frequently of figures of the more important varieties of each species, which will often relieve the young student from a state of puzzled suspense in the determination of his specimens. The classification adopted is founded, in its broad outlines, upon the preparatory states of the insects, but it leads pretty nearly to the same results as the system more generally followed.

The illustrations are very numerous, including figures of all the species and of both sexes when there is any difference either in the upper or lower surface. They are all woodcuts, and are generally well executed, as may be seen from the examples which we are enabled to give. W. S. DALLAS

OUR BOOK SHELF

The Western Chronicle of Science. Edited by J. H. Collins, F.G.S., Secretary to the Royal Cornwall Polytechnic Society. January to June, 1871. (Falmouth. Pp. 96.)

WE are glad to afford space for a short notice of this cheap scientific journal, which, although specially intended for the benefit of the mining population of Cornwall and West Devon, deserves a wide circulation in all our mining districts. Each monthly number contains one or two original articles, either on general subjects, as " The Practical Value of Scientific Knowledge," or giving descriptions of various forms of machinery, followed by notices of books, and a monthly chronicle of science. From one of the editorial articles on "The Practical Value of Scientific Knowledge," we learn that a good stoker may effect an annual saving of nearly 35. per annum over a bad one, and that it is a common Cornish habit to hang heavy jackets, great coats, &c., on the lever of the safety valve of engines devoid of a pressure guage; while the farmers, with the view of giving their ground two good things at once, mix lime with their guano some days before spreading the manure. A very remarkable natural-history statement is made by Mr. Williams, of Hayle, in his paper on "Scientific Nursing." "I have (he says) in my possession a double chick, the produce of an egg laid by a barn-door fowl, one half being the natural species, the other half composed of the sparrow-hawk!" Until this remarkable chick appears in propria persona at the office of NATURE, or, at all events sends us its photograph, we must, with much regret, decline to accept the fact. Medizinische Fahrbücher. Herausgegeben von der K. K. Gesellschaft der Aerzte, redigirt von S. Stricker. Jahrgang, 1871, Heft I. und II. Mit 26 Holzschnitten und 2 lithographirten Tafeln. (Vienna: Braumüller; London: Williams and Norgate, 1871.)

THE two parts before us are the continuation, in a new form, of an old and valuable periodical, and, under Prof. Stricker's able editorship, its tendency, instead of being, as heretofore, chiefly clinical, will be so far modified as to embrace all the results obtained in the physiological laboratory. A glance at the table of contents is sufficient to prove the truth of this statement. Thus putting aside the first paper by Prof. Stricker, entitled "Pathology and Clinical Observation;" the rest, nine in number, are nearly all devoted to the results of microscopic research. Thus, Dr. Genersich contributes a paper on the Serous Canals of the Cornea; Dr. Heiberg one on the Regeneration of the Corneal Epithelium; Dr. Güterbock one on Inflammation of Tendons; Dr. G. F. Yeo one on the Structure of Inflamed Lymphatic Glands; Dr. Lang one on the First Stages of Inflammation in Bone; Dr. Albert and Dr. Stricker one on Surgical Fever, and the latter author another on the nature of the Poison of Pus, and so on. The journal leads off with a good start, and if it continues as it has commenced, will probably take up a leading position. We notice one or two of the papers that appear to be of general interest. H. P.

LETTERS TO THE EDITOR [The Editor does not hold himself responsible for opinions expressed by his Correspondents. No notice is taken of anonymous communications.]

Cotteau's "Echinides de la Sarthe "

A NOTICE of Cotteau et Triger's Echinides de la Sarthe in a recent number of NATURE (June 15, p. 120) is likely to convey a false impression of the accuracy of M. Cotteau, and throws considerable doubt on the value of his work. It is not often that French scientific men are as conscientious as he is in the examination of authentic types. There is hardly a collection of fossil Echini which M. Cotteau has not examined; and his

thorough acquaintance with all that has been written on his subject, as well as his intimate correspondence with the principal echinologists, is a sufficient guarantee that no important memoir (such as Wright's monograph) could have escaped him. Anyone who will take the trouble of turning to Cotteau's work (p. 111) will find, under Pseudodiadema hemisphæricum, a notice of Dr. Wright's figure of the same species (so much superior, with many others, to Cotteau's?) and a reference to his description. Nor is this an isolated case. Throughout the work M. Cotteau discusses and criticises more or less the results of this very monograph, said to have been overlooked by him. The mistake Cotteau is accused of making of assigning to Desor instead of Agassiz the specific name of Pseudodiadema hemisphæricum is entirely unfounded. Referring again to p. 111., we find, as a synonym, Diadema hemisphæricum" Agass. M. Cotteau, like many continental and American writers, does not interpret the notation of species as is required by the laws of the British Association, but for that reason he should not be accused of committing mistakes which his own writings show him not to have committed. M. Cotteau, in common with others, looks upon nomenclature simply as a matter of registration; and when M. Desor transfers to Pseudodiadema the Diadema hemisphæri cum Agass., M. Cotteau writes, therefore, Pseudodiadema hemisphoricum Desor, and not Agassiz; he may be wrong, according to the principles of the writer in NATURE, but he has not, either in this instance or in the other cases alluded to, committed a mistake through ignorance of the subject. A. AGASSIZ

Mr. Howorth on Darwinism

MR. HOWORTH sneers at "Survival of the Fittest" as an "identical expression" which "might have suggested itself even to a child," an axiom, in short, of which the truth cannot be disputed. This is satisfactory; but it is strange that he did not apply this axiom to his own theory, and see how they agreed together. He would probably admit, as another discovery "that might have suggested itself to a child,” that as a rule the entire offspring of each animal or plant, except the one or two necessary to replace the parents, die before they produce offspring (this has never been denied since I put it prominently forward thir een years ago). He would further admit, I have little doubt, that a great majority of animals and plants produce during their lifetime from ten to a thousand offspring, so that fifty will be a low average, but the exact number is of no importance. Forty-nine. therefore, of every fifty individuals born, die before reaching maturity; the fiftieth survives because it is "best fitted to survive," because it has conquered in the struggle for existence. Will Mr. Howorth also admit as self-evident, that this one survivor in fifty is healthy, vigorous, and well nourished, not sickly, weak, or half-starved? If he maintains that it is the latter, I shall ask him to prove it; if the former, then what becomes of his theory as an argument against Natural Selection? For, admitting as a possibility that his theory of the greater fecundity of the weak, &c., is true, how are these weak or sickly parents to provide for and bring up to maturity their offspring, and how are the offspring themselves (undoubtedly less vigorous than the offspring of strong and healthy parents) to maintain themselves? The one in fifty who survives to leave descendants will inevitably be the strong and healthy offspring of strong and healthy parents; the forty-nine who die will comprise the weaker and less healthy offspring of weak and sickly parents; so that, as Mr. Darwin and myself have long ago shown, the number of offspring produced is, in most cases, the least important of the factors in determining the continuance of a species.

I have thought it better to go thus into the heart of the question, rather than defend myself from the charge of dogmatism, for stating as a fact that the most vigorous plants and animals are the most fertile. I repeat the statement, however, referring to Mr. Darwin's observations, and especially to those in which he demonstrates by experiment that cross-breeding produces the most vigorous and luxuriant plants, which again produce by far the largest quantity of seed. The facts that wild animals and plants are, as a rule, healthy and vigorous, that the head of the herd is the strongest bull, and that weak and sickly carnivora are rarely found because they must inevitably starve to death, sufficiently refute Mr. Howorth's theory as against Natural Selection. If he can point to any district upon the earth where the animals and plants are in a state of chronic debility, disease, and starvation,

I may admit that there his theory holds good; but such a district has not yet come under my observation, or, as far as I am aware of, been recorded by any traveller.

I still maintain (Prof. Jowett's authority notwithstanding) that the phrase "Persistence of the Stronger" does not truly represent "Natural Selection" or the struggle for existence;" and, though it may often be true, is not the whole truth. The arguments of Mr. Howorth from the history of savages will, I think, not have much weight, if we may take as an example his putting together as cause and effect the extinction of the Hottentots and their now obtaining enough to eat. ALFRED R. WALLACE

MR. ALFRED WALLACE directs attention to the gross error of supposing that "the struggle for existence means the persistence of the stronger," and correctly stigmatises this view of Mr. Howorth's "a pure misrepresentation.'

66

It is, as Mr. Wallace remarks, very curious and even ludicrous, after all that has been said and written upon the matter, that anyone should fail to recognise the advantages to their possessor of "obscure colours,' "cunning,' nauseousness," "bad odour," and other qualities superior to strength alone. The creature having these properties, at last brought to perfection through the operation of natural selection, acting through countless generations, will assuredly have the advantage in the battle of life over its less fortunate neighbours. It will survive in the struggle for existence. Having survived, is it not better that it should at once teach the world the law of its survival, and proclaim itself the fittest to survive, than that it should remain silent until those whom it has destroyed may rise from the dead and admit that their doom was deserved because they were not fit to live? LIONEL S. BEALE

MR. HOWORTH, it seems to me, has not chosen a very favourable time for so strongly maintaining the truth of Mr. Doubleday's theory, seeing that the recent census has shown that the population of England has increased not only with an increment absolutely greater than that shown by any previous census, but also and this is still more important-with an increase proportionally greater than during the last decade. Yet never, surely, has luxury been so prevalent among us as during these last ten years. The evidence thus afforded will perhaps be deemed more conclusive than the argument of Mr. J. S. Mill, who invites those who may be inclined to accept Mr. Doubleday's opinions "to look through a volume of the Peerage, and observe the enormous families almost universal in that class; or call to mind the large families of the English clergy, and generally of the middle classes of England" (" Principles of Political Economy," bk. 1, ch. x., note). Mr. Howorth, however, states that "the classes among us who teem with children are not the well-to-do and the comfortable." If this statement were absolutely true, it wou'd be of little service to Mr. Howorth, since it is in the classes referred to that prudential restraint acts with the greatest force, and the effects of this restraint, both direct and indirect, would have to be taken into account before his conclusion could be admitted. He further asserts that "a state of debility of the population induces fertility," since "where mortality is the greatest there is much the greatest fecundity." That births should be most numerous where the mortality is greatest, requires for its explanation no hypothesis respecting the fertilising power of debility. "The fact," says Malthus, may be accounted for without resorting to so strange a supposition as that the fruitfulness of women should vary inversely as their health. When a great mortality takes place, a proportional number of births immediately ensues, owing both to the greater number of yearly marriages from the increased demand for labour, and the greater fecundity of each marriage from being contracted at an earlier, and naturally more prolific, age" (vol. i., pp. 472, 473, 5th edit.). Man's reproductive power is always in civilised life more or less checked, and ready to be more or less exercised in proportion to the lessening by death of the restraining pressure.

THOMAS TYLER

MR. WALLACE, in replying to Mr. Howorth's objections to the theory of Natural Selection, points out that that gentleman first misrepresents Darwinism, and that having done so he does not employ the distorted doctrine as premisses to a further con

clusion. But the second part of the criticism is not quite just. Mr. Howorth, after stating the Darwinism theory, introduces us to an order of facts which is at variance with that theory as apprehended by him; and not only does he do so, but he places an interpretation upon these facts which is utterly irreconcilable with the Darwinian theory as understood by its most able expositors. It is true that Mr. Howorth does not bring his interpretation of the facts he adduces and the theory of natural selection into such juxtaposition as to show their mutual contradiction; but a little consideration will enable Mr. Wallace to supply the missing links, and to see that in any generous construction of Mr. Howorth's letter, the real questions at issue are the correctness of the facts he adduces and the validity of the generalisation he makes from these facts. My object in writing is to direct Mr. Howorth's attention to Mr. Herbert Spencer's profound discussion of this subject, as it appears to have escaped his notice. This is the more surprising, since, on p. 111, vol ii. of "The Variation of Animals and Plants under Domestication," and to which Mr. Darwin refers him, there is the following marginal note:-" Since this MS. has been sent to press, a full discussion on the present subject has appeared in Mr. Herbert Spencer's Principles of Biology' vol ii., 1867, p. 457, et seq.' He is a bold man who undertakes to enlighten the public on a subject which Mr. Spencer has fully discussed, without first ascertaining what view that profound and original thinker adopts; and most certainly a fresh writer coming into the field ought to take up the discussion where an author of such eminence has left it.

If Mr. Howorth will look at Mr. Herbert Spencer's "Principles of Biology," he will find in sections 78 and 79, an explanation of the process adopted by gardeners of cutting the roots, and "ringing" the bark of fruit trees. Section 355 explains the fact that farness is often accompanied by barrenness. In a footnote at p. 483, vol. ii., he will find Mr. Doubleday's doctrine specially noticed, and the fallacies upon which it is based exposed; while in the chapters "On the Laws of Multiplication," vol. ii., p. 391, et seq., he will find the whole subject treated with a fulness and exhaustiveness which leaves little to be desired. Mr. Howorth will notice that Mr. Spencer does not deny Mr. Doubleday's facts, but that he places upon them an interpretation which brings them into harmony with the general theory of evolution, and with the special part of organic evolution which constitutes the Darwinian theory. Newchurch, July 17 JAMES ROSS

I HOPE you will allow me a few lines to reply to Mr. Howorth. I had thought Mr. Doubleday's essay was among the things of the past. There can be no question that his conclusions are not the conclusions of accomplished naturalists like Mr. Wallace, whose assertions are certainly as good, if not far better, than those of Mr. Doubleday.

Quoting Mr. Chadwick, Mr. Howorth again puts cause for effect. There can be no doubt that the death rate increases in a crowded country pari passu with the crowding, and that the crowding is the result of fertility. It by no means follows that the crowding produces fertility.

There is one way in which poverty and overcrowding tend to ncrease the birth rate. Many of the children of the poor die during the first few months of life, and hence the mother, being relieved of her offspring, ceases to secrete milk, and soon again falls pregnant. It is the death of very young children in crowded districts which so largely increases the mortality, and this, as we have seen, may tend to increase the birth rate.

The large percentage of deaths in early life amongst the illnourished and weakly renders these less likely to bear children than the strong. With regard to the large families of the pour so often quoted, I have grave doubts of the fact. I have for many years seen hundreds of poor families every year in the exercise of my profession of surgeon, and although I know many instances of ten or fifteen children having been born of one mother, in the majority not more than two or three reached adult age, and hence these produced no offspring in the second generation.

The most remarkably prolific woman who has come under my notice has had twenty-two children in twenty years, and she is still continuing to present her husband with blessings. She is one of the fattest women I know.

Amongst the rich and the well-to-do it is no uncommon thing for eight or ten children to grow to man's and woman's estate and to rear families. I know as many well-to-do persons with large

families as poor people, and the living percentage is far greater in the former.

I am not aware that consumptive patients are so extremely prone to breed as Mr. Howorth thinks, certainly their children do not live to produce a second generation as a rule.

Examples of fecundity and barrenness amongst wild tribes are not much to the purpose, because there are so many disturbing influences. To take, however, Mr. Howorth's case, the Red Indian feeds ill enough and is thin enough, yet he is not fertile. The backwoolsman, with his vegetable diet, would be far more likely to grow fat, and is certainly far better fed and far stronger than the Indian, yet he is more fertile than the In fian, although by no means fertile. He has many hardships to undergo.

With regard to the Patagonian women and their belief that bleeding produces fertility, evidence is wanting as to the truth of their belief. We know many wide-spread beliefs are erroneous, for instance, most savages believe in rain makers.

In conclusion, Mr. Howorth thinks that wild animals in captivity are sterile from over-feeding. If he will try and make them fertile by starving them, I think I may assert positively he will fail. Hence, I suspect, we must look for a deeper cause of barrenness in them. B. T. LoWNE 99, Guilford Street

Recent Neologisms

IN using the word Mr. Ingleby objects to as hideous, I was not aware that I was coining a new one. If so, it was quite unconsciously on my part; but a word was wanted to express the property of being prolific, and if the choice lies between and 66 “prolificness" prolificacity," as I think it does, I am inclined to believe that the former will survive, as being the shorter, the easier to pronounce, and perhaps the less hideous, even though it may not be constructed on the best etymological principles. "Fertility" and "fecundity," which are often used, do not quite answer the purpose, although the latter has very nearly the same meaning. Our language must and will grow; and its growth will be determined by convenience rather than by gram. matical rules. ALFRED R. WALLACE

In his excellent custom of "registering the first appearance of new words and new phrases," Dr. C. M. Ingleby is surely very careless or superficial. He quotes "survival as a new word introduced, he thinks, by Darwin. I have been familiar with it as long as I remember, and my life of careful observation has exceeded a quarter of a century. "Impolicy" is equally familiar, having had currency at least twenty years before the Franco-Prussian war, to which Dr. Ingleby accredits it. He will find both words, as well as "indiscipline," in "Webster's Dictionary," edition 1852, and probably much earlier on careful search. "To telegram" is clearly a vulgarism, rarely heard I imagine, and never seen in print. G. W. S.

Fertilisation of the Bee Orchis

MR. DARWIN, in his "Fertilisation of Orchids," states his belief that the Bee Orchis presents a physiological difference from all other British orchids, and is habitually self-fertilised. I had, yesterday, an opportunity of observing a number of these plants in one of its abundant localities in Surrey, and at a time when fertilisation must have been completed. In every plant almost all the capsules were considerably swollen, and were loaded with apparently fertilised ovules. In most of the withered flowers, the remains of the pollinia were still visible in the posi tion described by Mr. Darwin, hanging down before the entrance to the nectary, in immediate proximity to the stignia, and render. ing it almost impossible to believe that the flower had ever been

entered by any insect of considerable size, which must inevitably have carried away the pollinia with it. The fact that the Bee Orchis, the most "imitative" of all our native plants, is never visited by insects, is a very suggestive one. If, as might well have been assumed, the object of the "mimicry" is the attraction of bees, the device appears to have signally failed. London, July 17 ALFRED W. BENNETT

Saturn's Rings

As Lieut. Davies has thought it necessary to refer to your remarks about the satellite theory of Saturn's rings-and in so doing has named my work upon Saturn (which you had only referred to without naming) it may be as well for me to mention, that I nowhere in that work claim the theory as mine-and that, whenever I have seen it referred to as mine, I have as publicly as possible disclaimed all title to it.

Permit me to add, that, whatever opinion we form of Lieut. Davies's views, he deserves our thanks for bringing out a treatise so full of work, from cover to cover, as his "Meteoric Theories." Such examples are a good deal needed in these days.

8, Wellington Villas, Brighton RICHARD A. PROCTOR

Ocean Currents

I FIND that Dr. Carpenter does not consider his experimen probative. Judging from the air of triumph with which, both in his lectures and writings, he has announced its success, I had certainly imagined that he did. But if not probative, what is it? Dr. Carpenter says it is only intended to be illustrative. What does it illustrate? It does not illustrate any currents formed in the ocean by differences of temperature; for it does not illustrate the differences of temperature to which he attributes these currents. In his letter in NATURE of July 6, he proposes an unwieldy modification of his former well-known experiment, but which still, I would submit, in no way avoids the difficulty to which I have called attention. He describes a strong freezing mixture applied to the surface through one-tenth of the length of a trough half a mile long, and heat applied to the surface also through one-tenth of the length, measured from the other end : between the cold and the hot surface there is, then, an intervening space of four-tenths of a mile, or 2,112 feet; that is to say, there is a thermometric gradient of about 50° in 2,000 feet, or 1 in forty feet. This is small enough, and we may perhaps doubt whether such a gradient could give rise to any appreciable movement; but it is 15,000 times greater than the gradient observed in the ocean, which is about 1 in 100 nautical miles; and any movement shown by an experiment which, in its details, bears no reasonable proportion to the reality, cannot be accepted as an illustration of a movement in the ocean.

Mr. Proctor, in the same way, speaks of his proposed experiment as an illustration; and, in the same way, I would say that the distortion produced by magnifying 6,000,000 times that particular detail on which he wishes to lay an emphasis, precludes our accepting it as an illustration at all. Mr. Proctor says that it is intended specially to throw light on the easterly and westerly movements; it is surely unnecessary for me to point out to him that any easterly or westerly movements, as illustrated in a cylinder such as he describes, revolving continuously and uniformly, are direct consequents of the outward or inward movement due to the differences of temperature, and are, therefore, in the strictest sense, dependent on the thermometric gradient. If, with a thermometric gradient of of a degree in one foot, and with an angular velocity of 360° in 24 hours, Mr. Proctor succeeds in showing any appreciable movement, I and (I think I may add) many other readers of NATURE will be glad to learn the result. But this is, after all, the point I raised in my last letter (NATURE, June 29), and which Mr. Proctor considers would require many columns for its full discussion. I do not myself see that there is any room for discussion at all; and any difference of opinion that may exist can only be met by experimental demonstration.

Dr. Carpenter appears to wish to support his theory on "authority," and especially on that of the recent letter of Sir John Herschel. This is a point on which I touch with great reluctance; but I would point out, in the first place, that "authority" in matters of science carries very little weight; and, secondly, that Sir John Herschel, in the letter referred to, merely admits what he and everyone else have all along admitted, that hot water and cold, in juxtaposition, will establish a circu

lation. It was not for him, in a letter of private courtesy, to enter again on a discussion of the infinitesimal nature of the gradients a discussion which he had already worked out very fully in his "Physical Geography."

But, leaving this consideration on one side, I maintain that, at the present time, the onus probandi rests with the supporters of the temperature theory. Its opponents have offered what is, at any rate, a rational, consistent, and tolerably complete explanation of all the known ocean currents; and they say, in so many words, that the explanation offered, in accordance with the theory of temperature and specific gravity, is neither complete, nor consistent with itself or with geographical observation. The theoretical objection of the infinitesimal nature of the thermometric gradients and of the differences of specific gravity, which has, indeed, formed the subject of these letters, is not one which I was inclined to put forward in any prominent degree. I preferred, and still prefer, to base my objection on the utter discrepancy between fact as observed, and fact as described by Captain Maury and Dr. Carpenter, in accordance with their theory.

I have elsewhere dwelt on this at great length, and do not intend to go over the same ground here, even if you were willing to afford me the space to do so; but this discrepancy, which actually and very markedly exists, does call attention to the thermometric gradients in the ocean; and when we find the same discrepancy between observation and description in the case of aërial currents, it leads to the conclusion that the infinitesimal nature of the thermometric gradients is as sound an objection to the temperature theory of atmospheric circulation, as it is to the temperature theory of oceanic circulation. I refer here to the last sentence but one of Mr. Proctor's letter. The last sentence, I must confess, I do not understand. I do not see what effects solar light can produce, or even be supposed to produce, on the depths of ocean, to which no light penetrates; still less do I see how to integrate them. J. K. LAUGHTON

Formation of Flints

In your report of the discussion that followed the reading of my paper on Flint, before the Geologists' Association on June 2nd, Prof. Morris is said to have asserted that the views I suggested were first propounded by Dr. Brown of Edinburgh. I think the Professor must have been slightly misrepresented in this; at all events I must most decidedly decline to be coupled with Dr. Brown, or to allow myself to be associated with his very remarkable statements. These may be found in the Trans. Roy. Soc. Edinb., vol. xv. He asserts that carbon is transmutable into silicon; at p. 229 he says, "Carbon and silicon are isomeric bodies, and that the former element may be converted into a substance presenting all the properties of the latter." At p. 244, "304 grains of silicic acid were extracted from 5 grains of paracyanide of iron;" at p. 245, " 5'4 grains of silicic acid were procured from 30 grains of the ferrocyanide of potassium," and there were obtained 9,334 grains of silica from 3,240 grains of ferrocyanide, although some of the product was lost in two of the operations." The view I advocated as explanatory of the formation of flints was the substitution of silicon for carbon, not a transmutation, and I distinctly showed the source from which the silicon was derived. Dr. Brown's statements are so extraordinary that I could scarcely believe them serious. I find, however, in the same volume of the "Transactions" that they were most patiently examined and confuted by Dr. George Wilson and Mr. John Crombie Brown, and they say, "We tried the greater number of Dr. Brown's processes, and rejected them one after another without pursuing their investigation further, on finding they would not yield quantitative proofs of the conversion of carbon into silicon. The limited time, which from various circumstances we could devote to the subject, obliged us to follow this course; and the confident expectation we entertained till a recent period that each new process would supply what the rejected ones had failed to afford, led us to neglect noting many particulars of our early trials which otherwise we should have recorded. . . . In conclusion, we need scarcely say that we have been unable to supply any proof of the transmutability of carbon into silicon."

I have one more objection to make to the report. I did not say that flints were merely silicified sponges. I believe that such is the case with some flints, but certainly not with all. I hope you will find space for this rectification of manifest errors. M. HAWKINS JOHNSON

379, Euston Road, July 11