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perimeter was very rough. This change in the variation of c with relation to the s lope was found to depend upon the hydraulic radius being greater or less than 3'281 feet; so that becomes independent of the change in slope when R approximates to this value, though the actual value of R at which the modification occurs varies with the degree of roughness of the channel. This result is attributed to the conflicting currents and eddies in large rivers having irregular beds, or in small channels with very rough beds, which are intensified by an increase in the slope; whereas, in small streams flowing in confined channels with smooth beds, an increased velocity tends to dissipate retarding lateral movements. A preliminary

form adopted for the value of c was

n

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a+replaces y in the original formula, and an = x, or x = ny - 7, in which a is a constant with value 41.66 in English measures; is another constant, equal to R when R has the special value 3:281 referred to above, and therefore 1.811; and n is the coefficient of roughness, varying, according to the state of the channel, from 0'009 to 0040. The above value of suffices for the flow in pipes and other small channels with steep slopes, owing to the small influence of a variation of slope on the coefficient c in such cases; but for ordinary channels allowance has to be made for variations in slope, necessitating the introduction of another variable factor into the expression for c. The final shape given to the value of c by Messrs. Ganguillet and Kutter, in their general a+ +

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for English measures, is a constant of a hyperbola employed in constructing the formula. The general formula, accordingly, became, for English measures

will be required. The authors, however, of the form '• do not regard it as final or complete, nor do they cl for it any mathematical precision; they only consider that it agrees more closely than any previous forms: with the results of recorded observations. The forma has naturally been objected to on account of its g plicated appearance; but the variation due to change t slope renders this inevitable; and it has been seen that a simpler formula may be adopted for pipes, and sma channels with steep slopes; and, moreover, graphu methods and tables might simplify the calculations. A the close of last year, Mr. Robert Manning, Engineer to the Board of Works in Dublin, presented a new formet. to the Institution of Civil Engineers of Ireland, which, ri its general form, is hardly less complicated than that of Messrs. Ganguillet and Kutter. This formula is

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where n is the coefficient of roughness, g the force ve gravity, and m the height of the barometric colum. of mercury. Mr. Manning puts it forward as simpler and better than the other, and claims for it, in a simplites form, a closer approximation to the mean of the result of seven of the best known formule than any other Actual observations, however, form a surer basis up which to establish a general formula than the results of previous formulæ ; and it is upon a close concordance very varied and accurate observations that any gene formula must claim acceptance. Whatever position may in the future be assigned to the formula of Messrs. Ganguillet and Kutter, their work marks a notable step a advance, and must rank with the researches of Messrs. Darcy and Bazin, and Messrs. Humphreys and Abbot, as a record of important hydraulic investigations; and the translators have performed a valuable service in placing

clearly before English readers the successive steps by which this general formula has been established.

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where V is the mean velocity in feet per second, which multiplied by the cross-section would give the discharge in cubic feet per second, and S is the actual slope.

The main interest of the book consists in the clear exposition of the several steps by which the formula was reached; and even if at some future time, by the aid of fresh observations and more accurate experiments, the formula should be superseded by a more comprehensive and exact one, the merit of this work as an elaborate scientific investigation for a general empirical formula must always remain; and the book would deserve to be consulted on this ground alone. The formula depends entirely upon the exactness of the observations upon which it has been based. Mr. Révy has questioned the accuracy of the Mississippi experiments, owing to the use of double floats; and if fresh investigations should establish the inaccuracy of any of the observations made use of, or if further experiments should extend the scope of the inquiry, or bring new facts to light, a modified formula

THE COMPASS ON BOARD.

Der Kompass an Bord: Ein Handbuch für Führer-e eisernen Schiffen. Herausgegeben von der Direkt " der Deutschen Seewarte. (Hamburg: L. Friedenches and Co., 1889.)

THE important subject ofviations of their compass

HE important subject of the magnetism of iron ships

has, during the last fifty years, received marked attention in England from eminent men of science, attended with most valuable results for the safe navigation of our Rova and mercantile navies.

During the last thirteen years this same subject h been one of continuous inquiry at the German Nava, Observatory in Hamburg, and papers have been publishe from time to time in the annual report of that institution showing what had been accomplished. Combining the results of this work with those obtained from the extensive literature chiefly produced in England, Dr. Neumayer. the Director of the Observatory, has compiled the prese work for the use of officers commanding the iron ships of the German mercantile navy.

Of the six chapters into which the work is divided, the first is devoted to information on the magnetism of ir

and steel, terrestrial magnetism, and the means of has a chapter devoted to it, containing information which obtaining the three magnetic elements.

In the second chapter, the various modern forms of the mariner's compass, and instruments for adjusting compasses without sights, are described with illustrations. There is much here which should be of value to commanders of ships anxious to know as much as possible of their best friend in navigation.

It is, however, to be regretted that in some particulars both text and illustrations belong to the past, for in Fig. 38 an imperfect idea is given of Sir W. Thomson's compass. The drawing was correct for 1877, but important improvements were made ten years ago in the substitution of the wire grummet suspension for india-rubber, a change attended with marked success in vessels propelled and severely shaken by powerful engines; also, in 1881, the adoption of a total reflection prism in the azimuth mirror instead of an ordinary piece of looking-glass.

Prominence is given to the Hechelmann compass card, which is intended to combine the principles of the Thomson card (which consist chiefly of a long period of oscillation and great lightness), with a much greater magnetic moment in the Thomson-Hechelmann card, as it may be termed. The chief difference in these cards bes in the arrangement of the needles, Hechelmann's idea being to suspend more powerful needles than Thomson's near the circumference, thus bringing the weight as far as possible from the centre of the card to produce a slow period.

In bringing powerful needles so near the circumference, it is easy to see that something has been lost by Hechelmann when the quadrantal deviation is to be corrected as it should be a correction so perfectly accomplished by Thomson. The greater weight of the card, too, tends to increase friction at the cap and pivot. Under these considerations the Thomson-Hechelmann card can hardly be considered equal to the modern Thomson.

In the next chapter, which treats of the magnetism of ships and the resulting deviation, it is satisfactory to find that the different kinds of magnetism which careful investigation has shown to exist in modern vessels are specially mentioned. These are

(1) Permanent magnetism.

(2) Sub-permanent (termed also retentive) magnetism. (5) Transient magnetism.

These definitions are accompanied by a footnote stating that in the English text-books on deviation no difference is made between permanent and sub-permanent magnetism, but that the two are combined under the expression sub-permanent. This is perhaps rather hard upon some English books, where, by careful reading, it will be found that the distinction is really made, but, it must be confessed, with a want of that clearness of division which is important to sound knowledge. Readers of the papers published by the Royal Society, and more recently by the Royal United Service Institution, will find that the division of a ship's magnetism into the three kinds mentioned above is strongly insisted upon.

A complete analysis of the deviations of any given compass in a ship, and of the changes which take place on a change of latitude, is necessary before a satisfactory compensation of the deviation by magnets and soft iron can be made. In the "Compass on Board," this analysis

should be of value both to the captains of ships and compass adjusters. It is illustrated by many examples.

Values of the coefficients v and v', representing the temporary deviation caused by running on a given course for some days, are given for a number of vessels of different types, steam and sailing. They clearly show the navigator of a new ship the need of caution when altering course, and some idea of the amount of change of deviation he may expect; whilst it should be understood that no careful seaman would fail to learn and note the peculiarities of the iron affecting his ship's compasses from personal observation under the varied circumstances experienced during each voyage.

A corrector for the deviation caused by sub-permanent magnetism has yet to be discovered.

Taking a general view of this book, it may be described as calculated to provide good practical information for the officers of the German mercantile navy, as well as a certain amount of a theoretical nature for those inclined to learn something of a ship's magnetism from a higher standpoint.

The maps of the three magnetic elements provided at the end of the book are given for the epoch 1885, and on a larger scale than those usually provided in hand-books. The accompanying map of values of the secular change is somewhat open to criticism as regards the figures recorded in the Red Sea, Bombay, East Indies, and Australia. This, however, will not prove of any detriment to safety in practical navigation.

The difficulties connected with the compass in warships, with their armoured deck, thickly-plated sides, and conning-towers, are not treated of, and their officers must look elsewhere for the special information they require ; still, there is much to be found in this book that will serve their purpose.

OUR BOOK SHELF.

Library Reference Atlas of the World. By John Bartholomew, F.R.G.S. (London: Macmillan and Co., 1890.) THE recognition of the intimate connection that exists between physiography and geography is made very manifest, in all the atlases published during the last few years, by the insertion of maps indicating the physical

features of the earth's surface.

We are in an eminently utilitarian age, and a collection of maps, to meet the requirements of the day, must serve of places; it must represent the most permanent features more purposes than that of a mere index to the positions of importance in commercial geography, and the distribution of commodities as explained by the sciences of physics, geology, meteorology, biology, &c., or collectively by physiography. The elegant work before us satisfies all these requirements, it is as complete as it is a trustworthy atlas of modern geography, and will be equally appreciated by the student, the business man, and the general reader.

The atlas contains 84 maps, and amongst them we find plates delineating drainage areas, ocean currents, prevailing winds, rainfall, temperature, climate, and commercial features. A characteristic of the collection is the large number of maps that have been devoted to the Kingdom alone. British Empire, eighteen plates being given of the United India is completed in eight plates, the Dominion of Canada is very completely represented in seven plates, and the mapping of all the British possessions

has been carried out on the same elaborate scale. After the British Empire, special prominence has been given to the United States, whilst all the other countries of the world have been treated in a very comprehensive manner. The general reference index comprises the names of 100,000 places contained in the maps, and for British names it is the most complete ever published. One matter of regret, however, is that the places on some of the maps are not obviously visible because of the bright and superabundant colouring used to indicate the divisions of a country, for, generally speaking, these divisions are better represented by coloured lines. The less masking there is, the more distinct must places appear, and therefore the purpose of an atlas will be the better served. This is, however, but a minor point. The atlas is an excellent one, it is complete and accurate, contains all the results of recent exploration and geographical research, and is issued at a moderate price; its addition to every library therefore is a thing to be desired. The Bala Volcanic Series of Caernarvonshire and Associated Rocks; being the Sedgwick Prize Essay for 1888. By Alfred Harker, M.A., F.G.S., Fellow of St. John's College, and Demonstrator in Geology (Petrology) in the University of Cambridge. (Cambridge: University Press, 1889.)

IN this useful little work, Mr. Harker has given an admirable résume of the results which have, up to the present time, been arrived at by the study of the ancient igneous rocks of North Wales. Besides summarizing the work of the late John Arthur Phillips and E. B. Tawney, of Prof. Bonney, Mr. Rutley, Mr. Cole, Mr. Teall, Mr. Waller, Miss Raisin, and others who have written on the petrography of the district, he has added many new and often judicious notes on the rocks in question. A number of fresh analyses, and the description of hitherto unrecog nized varieties of rocks and minerals, raise the work out of the category of mere compilations; and the excellent classification and arrangement of his materials make the book one eminently useful for purposes of reference. It is unfortunate that it has no index, though the "table of contents," which is very full and carefully paged, causes the want to be less felt than it otherwise would be. Mr. Harker classifies the districts of Caernarvonshire in which volcanic rocks are found as the Eastern, North-Western, and Western, the latter consisting of the Lleyn peninsula. He groups the types of rocks represented under the headings of "rhyolitic lavas," "nodular rhyolites," "acid intrusives," "intermediate rocks," "diabase sills and basalts," and "other basic intrusions." The work concludes with a "review of vulcanicity in Caernarvonshire," in which we find discussions of the relation of the volcanic eruptions to the earth-movements that took place at the period of their occurrence, the succession of lavas in the district, and the evidence in favour of their submarine origin. The book is admirably printed, and is illustrated by six very clearly-drawn sketch-maps. The essay is worthy of the memorial in connection with which it appears, and is creditable to the University under whose auspices it is issued; and higher praise than this it would be difficult to give to any work

of the kind.

LETTERS TO THE EDITOR. [The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE, No notice is taken of anonymous communications.]

The Inheritance of Acquired Characters. WITHOUT expressing any opinion upon the question recently discussed in your columns under the above title, I think it may

be as well to recall the belief of one whose judgment was ne without weight, and to give some of the evidence on which th belief was founded.

sixth edition), Mr. Darwin says, respecting the inherited effo In the first chapter of the "Origin of Species" (p. 8 of the of habit, that "with animals the increased use or disuse of par has had a more marked influence"; and he gives as instances changed relative weights of the wing-bones and leg-bones of twild duck and the domestic duck, and, again, the drooping eas of various domestic animals. Here are other passages taxa from subsequent parts of the work:

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"I think there can be no doubt that use in our dome animals has strengthened and enlarged certain parts, and disk diminished them; and that such modifications are inherited (p. 108). And on the following pages he gives five further examples of such effects. "Habit in producing constitunon peculiarities, and use in strengthening and disuse in weakening and diminishing organs, appear in many cases to have bee "When discussing spel potent in their effects "(p 131). cases, Mr. Mivart passes over the effects of the increasel u and disuse of parts, which I have always maintained to be highar important, and have treated in my Variation under Domesti tion' at greater length than, as I believe, any other winter (p. 176). "Disuse, on the other hand, will account for the le developed condition of the whole inferior half of the body, y cluding the lateral fins" (p. 188). "I may give another instance of a structure which apparently owes its origin exclusively to use or habit" (p. 188). "It appears probable that disuse has been the main agent in rendering organs rudimentary" (PP. 400-401. have, in some cases, played a considerable part in the molis "On the whole, we may conclude that habit, or use and disa tion of the constitution and structure; but that the effects have often been largely combined with, and sometimes overmasterel by, the natural selection of innate variations" (p. 114).

In his subsequent work. "The Variation of Animals and Plants under Domestication," he writes :—

"The want of exercise has apparently modified the prop tional length of the limbs in comparison with the body” įr rabbits] (p 116). "We thus see that the most importani an complicated organ [the brain] in the whole organization is subject to the law of decrease in size from disuse" (p. 120). He remarks that in birds of the oceanic islands "not persecuted by any enemies, the reduction of their wings has probably been caused by gradual disuse." After comparing one of these, the water-hen of Tristan D'Acunha, with the European water-her, and showing that all the bones concerned in flight are smaller. he adds:-" Hence in the skeleton of this natural species near the same changes have occurred, only carried a little further, with our domestic ducks, and in this latter case I presume to one will dispute that they have resulted from the lessened usef the wings and the increased use of the legs" (pp. 286-87). “As with other long-domesticated animals, the instincts of the sila moth have suffered. The caterpillars, when placed on a mulberry tree, often commit the strange mistake of devouring the base is the leaf on which they are feeding, and consequently fall down. but they are capable, according to M. Robinet, of again crawling up the trunk. Even this capacity sometimes fails, for M. Marth placed some caterpillars on a tree, and those which fell were not able to remount and perished of hunger; they were even in capable of passing from leaf to leaf" (p. 304).

With

Here are some instances of like meaning from vol. ii. :— "In many cases there is reason to believe that the lessened use of various organs has affected the corresponding parts in the o spring. But there is no good evidence that this ever follows at the course of a single generation. . . . Our domestic fowl ducks, and geese have almost lost, not only in the individual be in the race, their power of flight; for we do not see a chicken when frightened, take flight like a young pheasant.... domestic pigeons, the length of sternum, the prominence of itcrest, the length of the scapula and furcula, the length of the wings as measured from tip to tip of the radius, are all reduc relatively to the same parts in the wild pigeon." After detailing kindred diminutions in fowls and ducks, Mr. Darwin adde "The decreased weight and size of the bones, in the foregoing cases, is probably the indirect result of the reaction of the weakened muscles on the bones" (pp. 297-98). "Nathustus ha shown that, with the improved races of the pig, the shortens legs and snout, the form of the articular condyles of the occiput, and the position of the jaws with the upper canine teeth project ing in a most anomalous manner in front of the lower canine may be attributed to these parts not having been fully exercisel

These modifications of structure, which are all strictly inherited, characterize several improved breeds, so that they Cannot have been derived from any single domestic or wild stock. With respect to cattle, Prof. Tanner has remarked that the lungs and liver in the improved breeds are found to be considerably reduced in size when compared with those possessed by animals having perfect liberty.'... The cause of the reduced lungs in highly-bred animals which take little exercise is obvious" (pp. 290-300). And on pp. 301, 302, and 303, he gives facts showing the effects of use and disuse in changing, among domestic animals, the characters of the ears, the lengths of the intestines, and, in rious ways, the natures of the instincts.

Clearly the first thing to be done by those who deny the inheritance of acquired characters is to show that the evidence Mr. Darwin has furnished by these numerous instances is all worthless. HERBERT SPENCER.

LET me remind the readers of NATURE that the discussion which has been going on in these columns, between the Duke of Argyll and Mr. Thiselton Dyer, arose out of a reference in Mr. Wallace's book on "Darwinism" to the dislocation of the eyes of flat-fishes. Two views have been expressed as to the origin of this arrangement-the one endeavouring to explain it as a Case in which a sport" or congenital variation, had been elected and intensified; the other attributing it to the direct uction of the muscles of ancestral flat-fishes which had pulled the eye out of its normal position, the dislocation thus estabished being transmitted to offspring, and its amount increased by like action in each succeeding generation. In common with Mr. Wallace and other naturalists, I spoke of this latter hypothesis as one of transmission of an "acquired character.' The term "acquired character" was clearly enough defined by his example; it has been used in England for some years, and equivalent in German (erworbene Eigenschaften) has been defined and used for the purpose of indicating the changes in a parent referred to by Lamarck in the following words Philosophie Zoologique," tome i. p. 235, édition Savy, 1873):

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"Première Loi.-Dans tout animal qui n'a point depassé le terme de ses developpements, l'emploi plus fréquent et soutenu d'un organe quelconque, fortifie peu à peu cet organe, le eveloppe, l'agrandit, et lui donne une puissance proportionnée la durée de cet emploi; tandis que le défaut cons ant d'usage de tel organe, l'affaiblit insensiblement, le détériore, diminue ,rogressivement ses facultés, et finit par le faire disparaître.

Deuxième Loi.-Tout ce que la nature a fait acquérir ou perdre aux individus par l'influence des circonstances où leur ace se trouve depuis longtemps exposée, et par conséquent par "nfluence de l'emploi prédominant de tel organe, ou par celle "un défaut constant d'usage de telle partie, elle le conserve par ia generation aux nouveaux individus qui en proviennent, arvu que les changements acquis soient communs aux deux * ou à ceux qui ont produit ces nouveaux individus."

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The meaning of the term "acquired characters" is accordingly perfectly familiar to all those who have any qualification for discussing the subject at all. It is used by Lamarck, and has been used since as Lamarck used it. Naturalists are at present interested in the attempt to decide whether Lamarck was justifed in his statement that acquired changes are transmitted from parents so changed to their offspring. Many of us hold that he was not; since, however plausible his laws above quoted may & pear, it has not been possible to bring forward a single case in which the acquisition of a character as described by Lamarck and its subsequent transmission to offspring have been conclusively observed. We consider that, until such cases can be produced, it is not legitimate to assume the truth of Lamarck's second law. We admit, of course, the operation of the environment and of use and disuse as productive of "acquired characters"; but we do not find any evidence that these particular sharacters so acquired are transmitted to offspring. Accordingly it has been held by several naturalists recently (whom I will call The anti-Lamarckians, and among whom I include myself) that it nece sary to eliminate from Mr. Darwin's teachings that small amount of doctrine which is based on the admission of the

validity of Lamarck's second law. As everyone knows, Mr. Itarwin's own theory of the natural selection of congenital variations in the struggle for existence is entirely distinct from Lamarck's theory, and the latter was only admitted by Darwin as being possibly or probably true in regard to some cases, and of minor importance. Although Darwin expressly states that he

was more inclined to attach importance to Lamarck's theory in the later editions of the "Origin of Species," the anti-Lamarckians are convinced that it is conducive to the progress of knowledge to reject that theory altogether until (if ever) it is placed on a solid basis of observed fact; and in the meantime to try if it is possible to explain the cases which seem most favourable to Lamarck's view by the application of Darwin's own theory.

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It is essential for those who are not thoroughly familiar with Darwin's writings to note that this does not involve a rejection of the conclusion that the action of external conditions upon a parent may be such as to modify the offspring. That is an important part of Mr. Darwin's own theory, and, as I recently pointed out in NATURE, it is to such action of the environment upon the parent that Mr. Darwin attributed the origin of those congenital variations upon which natural selection acts. This disturbance of the parental body (I compared it to the shaking up of a kaleidoscope), and with it of the germs which it carries, resulting in "sporting" or "variation in the offspring, is, it should hardly be needful to state, a totally different thing to the definite acquirement of a structural character by a parent as the result of the action upon it of the environment, and the transmission to offspring of that particular acquired structural character. I am not concerned to inquire here whether, or how far, Prof. Weismann's theory of the continuity of the germ-plasm admits of the action of external forces on a parental body in such a way as to disturb the germ-plasm and induce variation. Prof. Weismann can very well defend his own views. All that I am concerned with-and that quite independently of the conclusions of Prof. Weismann-is whether it is or is not reasonable, useful, or indeed legitimate, to assume the truth of Lamarck's second law, in the absence of any direct proof that any such transmission as it postulates takes place. Those who think Lamarck's second law to be true have been urged to state (1) cases in which the transmission of acquired characters is directly demonstrated, or (2) cases in which it seems impossible to explain a given structure except on the assumption of the truth of that law. If they fail to

do this, they are asked to admit that Lamarck's second law is, unproven and unnecessary.

The response which has been made to this attempt to arrive at facts is beside the mark. Mr. Cope writes to NATURE merely asserting, "If whatever is acquired by one generation were not transmitted to the next, no progress in the evolution of a character could possibly occur,"--an opinion peculiar to himself, and certainly one which cannot be taken in place of fact. The Duke of Argyll then "interpolates" (to use his own word) a general statement of his beliefs, and in the last of his letters a statement of "what his position is." We really are not concerned in this matter with beliefs or positions. We want well-ascertained facts and straightforward reasoning from facts. The Duke of Argyll has not assisted us. When on a recent occasion he was asked to cite an instance of what he called "a prophetic germ in the adult structure of a plant or animal having, in his opinion, such claims to this title as he had ascribed to the electric organ of skates, the Duke was unable to reply. He wrote as a substitute something about embryological phenomena, which had nothing to do with the case. He has not yet ventured to stake his oftasserted right to offer an opinion upon zoological topics, on the reception which his attempt to deal with the details of a particular case of organic structure would obtain: in this, I think, he is wise.

The Duke similarly tries to evade the appeal to facts when he is pressed by Mr. Dyer to state cases of the transmission of acquired characters. In doing so, however, he has, it must be admitted, revealed an astonishing levity. He answers (par. 9 of his letter) that in all domesticated animals, and especially in dogs, we have constant proof that many acquired characters may become congenital. This is mere assertion; we require details. It is maintained, on the contrary, by anti-Lamarckians that the whole history of artificial selection, and of our domesticated animals, furnishes a mass of evidence against the theory of the transmission of acquired characters, since if such cases occurred they would be on record, and moreover would have been utilized by breeders.

The subsequent proceeding of the Duke is almost incredible. In the following paragraphs of his letter he gives up his contention that acquired characters are transmitted, coupling his retreat with unwarrantable charges against those who have lately raised the question as to whether this is the case or He correctly states what is meant by the term "acquired characters," and declares that this meaning has been expressly invented for the purposes of the present discussion by "for

not.

tuitists," and is "irrational." A more baseless charge was never yet made in controversy, nor a more obvious attempt to alter the terms of discussion so as to give some appearance of plausibility to a lost cause. The Duke, in fact, now at length tells us that he does not mean by "acquired characters what we mean. Why then did he "interpolate" his remarks on the subject and make use of the term?

If the meaning which the phrase has for the scientific world generally be insisted upon, we are now, it appears, to understand that the Duke of Argyll agrees with us: what we mean by "acquired characters" are not, he admits, shown to be transmitted.

The

"Fortuitists," the Duke says, "have invented a new verbal definition of what they mean by 'acquired.'" I have shown at the commencement of this letter that the term "acquired" is used to-day as it was by Lamarck. To the Duke this meaning is "new"--because he has either never read or has forgotten his Lamarck. If this be so, the Duke has been writing very freely about a subject with which his acquaintance is very small. alternatives are as clear as possible: either the Duke of Argyll knew the significance of the term "acquired characters" as employed by Lamarck, in which case it would have been impossible that he should charge those whom he calls "fortuitists" with having invented a new verbal definition of what they mean by "acquired"; or he did not know Lamarck's use of the phrase, and was therefore not qualified to offer an opinion in the discussion, nor to press his "beliefs" and "position" upon public

attention.

I have no time and you have no space to devote to a full exposure of the character of other assertions made in the Duke of Argyll's "statement of his position" which are as reckless and demonstrably erroneous as that concerning the meaning of the term "acquired."

Perhaps the most flagrant of these is the assertion that "the theory of Darwin is essentially unphilosophical in so far as it ascribes the phenomena of variation to pure accident or fortuity" (paragraph 4). Of course the Duke cannot be acquainted with the following passage from the "Origin of Species," sixth edition, p. 106; but if he has to plead ignorance of the writings not only of Lamarck, but also of Darwin, what is the value of his opinions and beliefs on Lamarckism and Darwinism? The words of Mr. Darwin referred to are these:-" I have hitherto sometimes spoken as if the variations, so common and multiform with organic beings under domestication, and in a lesser degree with those under nature, were due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our ignorance of the cause of each particular variation.

Whatever meaning the Duke may attach to the word "fortuity," it is mere empty abuse on his part to call the later Darwinians "fortuitists," and still less justifiable to insinuate that their investigations and conclusions are not guided by a simple desire to arrive at truth, but by the intention of propping up a worship of Fortuity. It is natural for the Duke to suppose it impossible to write on Darwinism without some kind of theological bias.

In conclusion, I venture to point out that the Duke of Argyll has (1) failed to cite facts in support of his assertions of belief in "prophetic germs," and "transmission of acquired characters "when challenged to do so; (2) that he displays ignorance of two of the most important passages in the works of Lamarck and of Darwin, whom he nevertheless criticizes, and in consequence of his ignorance completely, though unintentionally, misrepresents; and (3) that he has introduced into these columns a method of treating the opinions of scientific men, viz. by insinuation of motive and by rhetorical abuse, which, though possibly congenial to a politician, are highly objectionable in the arena of scientific discussion. February 22. E. RAY LANKESTER.

Physical Properties of Water.

As you inform me that my anonymous critic (ante, p. 361) does not intend to avail himself of the opportunity I gave him (through you) of correcting his misstatements about my Challenger Report, I must ask to be permitted to correct them myself.

(1) There is nothing whatever in my Report to justify the critic's statement that I "had never heard of Van der Waals' work... till the end of the year 1888." Yet this is made the basis of an elaborate attack on me!

What I did say was to the effect that I was not aware, till Dr.

Du Bois told me, that Van der Waals had given numerical es mates of the value of Laplace's K. I had long known, from the papers of Clerk-Maxwell and Clansius, the main feature Van der Waals' investigation. But I also knew that Maxwel had shown it to be theoretically unsound; and that Chauss had taken the liberty of treating its chief formula as a mere empirical expression, by modifying its terms so as to mak better fit Andrews' data. This paper of Clausius is apparer unknown to my critic, as is also my own attempt to el (on defensible grounds) a formula somewhat similar to tha Van der Waals.

(2) I said nothing whatever about the "Volume of Matter in unit volume of Water." Hence the critic's statement, "F. Tait's value is 0 717," is simply without foundation. I merely said that the empirical formula

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My critic speaks of a totally different thing (with which I wa not concerned), which may be a/4 or a/4/2, or (as I think s more plausible) a/8. But he says that liquids can be compo to o 2 or 0.3 of their bulk at ordinary temperatures and pro I was, and remain, under the impression that this overd be done only at absolute zero, and then no compression required.

sures.

There are other misrepresentations of my statements, quite grave as those cited. But it would be tedious to examine ther all. I have no objection to a savage review, anonymous or fo on the essential condition, however, that it be fair. It cer from what I have shown that this essential condition is absent. But my critic, when his statements are accurate, find, a." with the form of my work. I will take two examples of Us kind, and examine them.

(3) He blames me for not using C.G.S. units. The C lenger Reports are, as a rule, written in terms * understanie of" nautical men.

I wonder what such men would have s**

of me, in their simple but emphatic vernacular, if I had spoken of a pressure of 154,432,200 C.G.S. units, when I meant wha they call a "ton"; or, say, of 185,230 C.G.S. units, when I naut."

meant a

66

(4) I am next blamed for "mixing units."

I should think that if we could find a formula expressing a terms of a man's age, the average rate at which he can run, 3 for instance Ax(B - x) + C

?=

even my critic would express A in feet per second, and take a the mere number denoting the age in year. Would be, in all the world, insist on expressing r as denoting the ge seconds in order to prevent what he calls the mixing of un This is a case precisely parallel to the one in question.

Generally, I would remark that my critic seems to ha written much more for the purpose of displaying his owi knowledge than of telling the reader what my Report comart For at least three of the most important things in my Rej are not even alluded to:-the compressibility of mercury, it nature of Amagat's grand improvement of the Mans Desgoffes, and (most particularly) the discussion of the wond ful formula for the compressibility of water given in the splendid publications of the Bureau International.

P. G. TAIT

THE last volume of the Challenger Reports contains pajer various branches of science. The review which appeid & NATURE was not the work of one writer, and was therefore signed, but I have no desire to avoid taking full responsality for the part of which I am the author.

It will be convenient to reply to Prof. Tait in parag numbered to correspond with his own.

(1) Of course I fully accept Prof. Taits account of his k ledge of Van der Waals' theory at the time when his Céz Report was written, but I entirely dissent from his statem that what he said about it in the Addendum referred to ở thư review was to the effect" described above.

It is hardly possible to do justice to my own case with quoting freely, but I will compress as much as possible the

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