Nature

force would at once show that this is the case, and that the ultimate result of both laws is that the property of a given conductor which we call its "resistance" is a constant under certain

conditions.

Again, we greatly object to the common practice of dragging in Ohm's law in connection with the magnetic circuit. Since the reluctance of the iron parts is not independent of the flux, even the mathematical analogy is very imperfect. There is no real analogy at all, for in the magnetic case nothing flows, and there is no continual generation of heat while the flux exists. A comparison with Hooke's law about stress and strain would be much more sensible.

Bearing in mind that it is intended to be a beginners' book, and that much detail is therefore not to be expected in the more advanced and technical portions, these are really the best; indeed, the last two chapters give excellent summaries of the leading facts about the discharge of electricity through gases and about electrical oscillations. DAVID ROBERTSON.

OUR BOOKSHELF.

Lehrbuch der vergleichenden Mikroskopischen Anatomie der Wirbeltiere. Edited by Prof. Dr. A. Oppel. VII. Teil, Sehorgan, by Dr. V. Franz. Pp. x+417. Price 18 marks. VIII. Teil, Die Hypophysis Cerebri, by Dr. W. Stendell. Pp. x+168. (Jena G. Fischer, 1913-14.) Price 8 marks.

WE have on former occasions expressed a high opinion of the "Comparative Microscopic Anatomy of Vertebrate Animals," now appearing under the editorship of Prof. Oppel. The parts here noticed (Nos. 7 and 8) deal with the eye and pituitary body, and maintain the high standard set by the earlier parts. In systematising our present knowledge of the various forms assumed by the eye in vertebrates, Dr. Franz has utilised more than

ence.

650 papers published in recent scientific journals, and in the light of his own researches grouped a multitude of facts together, so that his text and numerous illustrations form a consecutive treatise as well as a most valuable encyclopædia for referHe describes the minute structure of each part of the eye in turn-the retina, vitreous body, pecten, choroid, ciliary body, etc., tracing the variations undergone by each throughout the ramifications of the kingdom of vertebrate animals. The opening chapter deals with the visual cells of amphioxus; the closing one with the structure of the eye of species in which the sense of sight has been impaired or lost from disuse.

Dr. Walter Stendell's monograph on the pituitary body is of particular value at the present time. Until some thirty years ago this apparently unimportant structure was regarded as merely an interesting morphological puzzle. Our estimate was suddenly changed in 1886, when Dr. Pierre Marie discovered that the remarkable disease he

described under the name of acromegaly was accompanied by a pathological enlargement of the It was then realised that what pituitary body. was supposed to be merely a small vestigial organ had a direct power of regulating and influencing the growth of the body. Embryologists, morphologists, physiologists, and pathologists then concentrated their attention on it, and the results of their labours may be seen in Dr. Stendell's pages, particularly in his long bibliographical list. We are glad to note he gives due prominence to the pioneer researches of Sir Edward Schäfer and of Prof. P. T. Herring. Thresholds of Science. Astronomy. By C. Flammarion. Pp. xi+ 191. (London: Constable and Co.) Price 2s. net.

THE name of the author provides a guarantee of the soundness of the principles and the accuracy of the details expounded in this elementary introduction to astronomy by the eminent French astronomer. The book is essentially one for young readers, and the subject-matter is presented in a manner both lucid and interesting. The numerous illustrations are good, and aptly illustrate the text.

Commencing with the physical conditions of the earth, its motion and the resulting phenomena are treated at length, special attention being paid to the functions of the sun. A survey of the heavens with the constellations follows, and our relation to the "fixed stars" is made plain. The members of the solar system are treated individually, and their relations to each other in the system are efficiently illustrated. While dealing with the moon M. Flammarion introduces an interesting feature in a revue of the various mythical "Journeys to the Moon." The book concludes with a brief discussion of comets, nebulæ, and star clusters.

are

Although, as told in a footnote, "M. Flammarion naturally uses French measures" throughout the book, and the equivalents of the kilogram and kilometre are given, it would probably have been better had our own system of units been employed. The exercise in mental arithmetic required to obtain an estimate of the

magnitude involved is very liable to break the

continuity of thought, especially among the class of readers for whom the book is intended. Bacon's New Contour Wall Map of Scotland. Scale, 1:316,800, or 5 miles to one inch. Size 48 by 60 in. (London: G. W. Bacon and Co., Ltd.) Price 16s.

THIS new edition of a well-known wall map will be welcomed in schools. It is drawn on a conical projection with true meridians of longitude and errorless parallels 55° 30′ and 58° north latitude. The main orographical features are shown in the familiar shades of green and brown, and sea depths in blue tints. The lettering is such that it does not interfere with the scheme of colouring, and the railways, which are shown in red, are easily followed. The map can be obtained mounted and varnished with rollers to hang on the wall, or mounted with eyelets and cut to fold.

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.]

Faraday's Views on Catalysis.

Ar the present time much attention is being given, both by chemists and by physiologists, to the mechanism of catalysis in heterogeneous systems. The interest of the question to physiologists is in connection with the mode of action of those catalysts produced by living organisms; these are called, for convenience, enzymes."

The extraordinary insight shown by Faraday into the nature of the various phenomena with which he had to deal is well known and needs no further comment. But, on this ground, the paper which he published in the Philosophical Transactions of the Royal Society for the year 1834, entitled "On the Power of Metals and other Solids to Induce the Combination of Gaseous Bodies," deserves more consideration by modern investigators than it usually receives. The paper is also to be found in "Experimental Researches in Electricity" (vol. i., pp. 165-94), and the references given to quotations below refer to the numbered paragraphs in that reprint.

Although Faraday's work was published before the introduction by Berzelius of the name catalysis," the combination of oxygen and hydrogen gases brought about under the influence of platinum and other solids, which is the subject of the paper before us, is clearly a case of this kind. In fact, the action of spongy platinum is given by Berzelius himself in illustration of the phenomenon.

The chief experimental fact of importance to the theory of the process, and demonstrated by Faraday in a number of different ways, is that the only condition necessary is the perfect cleanliness of the surface of the platinum (617). He points out that impurities of various kinds are readily condensed on the surface ("adsorbed," as we should say), from the air and even from ordinary distilled water. The presence of such films prevents that condensation of the gases which is requisite for their combination. In whatever waymechanical, as by rubbing with polishing powders (591, 592, 593); chemical, by treatment with concentrated mineral acids (600); or by heat (596)-these substances are removed, the platinum is made active. Of special interest is the fact that making it either anode or kathode in dilute sulphuric acid (588) is particularly effective, the formation of "nascent" oxygen on the surface in the former case being the more powerful, as would be expected. The difference between the clean surface and the dirty surface is shown by the way in which water, or gases developed on the surface by electrolysis, enter into closer contact with the clean surface and form uniform films, instead of drops or bubbles.

It is pointed out in paragraph 617 that the intervention of electrical forces is excluded by the fact that both anode and kathode are active. Chemical reaction between the platinum and oxygen is also excluded by the fact that nitrous oxide and hydrogen are caused to combine (572). In paragraph 618 further evidence that the effect is not due to the intervention of platinum in a purely chemical way is given by the fact that "the effect is evidently produced by most, if not all, solid bodies."

The reader will probably call to mind that it has been held by some observers that this and similar activities shown by platinum are to be explained by

the formation of intermediate compounds of the nature of oxides of platinum. The actual existence of such compounds has never been demonstrated, and the hypothesis did not commend itself to the acute mind of Faraday, whose explanation is of much interest. On account of the importance of the question I will quote the actual words used :-"They" (the phenomena under discussion) "are dependent upon the natural conditions of gaseous elasticity, combined with the exertion of that attractive force possessed by many bodies, especially those which are solid, in an eminent degree, and probably belonging to all; by which they are drawn into association more or less close, without at the same time undergoing chemical combinationand which occasionally leads, under very favourable circumstances, as in the present instance, to the combination of bodies simultaneously subjected to this attraction" (619). As we might put it now, gases are condensed on surfaces, losing thus the kinetic energy of their molecules, and, if capable of combining together, may be thus caused to do so. Could we have a clearer statement of adsorption and the part played by it in catalysis?

In further illustration of this "adsorption," Faraday proceeds to give some interesting examples of the condensation of water vapour and of air on the surface of various powders and on glass, pointing out in the latter case that there is no chemical affinity between air and glass. We note also that Faraday says that the vapour is condensed upon the substances. Again, "The gases are so far condensed as to be brought within the action of their mutual affinities at the existing temperature" (630), and "The platina is not considered as causing the combination of any particles with itself, but only associating them closely around it; and the compressed particles are as free to move from the platina, being replaced by other particles, as a portion of dense air upon the surface of the globe, or at the bottom of a deep mine, is free to move, by the slightest impulse, into the upper and rarer parts of the atmosphere" (631). As regards the adsorption of other substances on the platinum, we read "In fact, the very power which causes the combination of oxygen and hydrogen, is competent, under the usual casual exposure of platina, to condense extraneous matters upon its surface, which, soiling it, take away for the time its power of combining oxygen and hydrogen by preventing their contact with it" (632). We have here analogous phenomena in the action of enzymes, where an easily adsorbed substance, such as saponin, prevents the action of the enzyme by obtaining possession of the surface itself and thus excluding the condensation of the molecules between which chemical action is to be brought about. Although Faraday evidently regards condensation on surfaces as especially applicable to gases, it is clear that he considers the phenomenon to be of general Occurrence. He does not appear to have met with cases of adsorption of substances from solution in liquids, but he says "an analogy in condition exists between the parts of a body in solution and those of a body in the vaporous or gaseous state" (657). Is this statement to be looked upon as an anticipation of van 't Hoff's theory of solutions?

I will conclude my quotations from the paper with the following, which is worth bearing in mind at the present day "I am convinced that the superficial actions of matter, whether between two bodies, or of one piece of the same body, and the actions of particles not directly or strongly in combination, are becoming daily more and more important to our theories of chemical as well as mechanical philosophy. In all ordinary cases of combustion it is evident that an action of the kind considered, occurring upon the surface of the carbon in the fire, and also in the bright

part of a flame, must have great influence over the combinations there taking place" (656). The last sentence is interesting in connection with the work of Prof. Bone on surface combustion.

It is, perhaps, rather to be wondered at, since Faraday had gone so far in the interpretation of the phenomena, that he did not take the further step and bring them into relation with surface tension, to which Thomas Young had already directed attention.

In the application of these facts to the theory of enzyme action, the view was first definitely put forward by myself, so far as I know, in a paper in the Biochemical Journal, vol. i. (1906), pp. 222-27, that the "combination" between an enzyme and its substrate is of the nature of an adsorption. This view has received more and more support from work done by various investigators since that time. To mention one fact only, it has been found in the cases of several different enzymes that their activity is exercised in liquids in which they are completely insoluble, so that it must be the surface of the particles which is concerned. We know also that, in water, enzymes in general are in the colloidal state, a state in which chemical reactions obey laws which interfere with that of mass action in its simple form.

It is very doubtful whether intermediate compounds of a chemical nature play any part in catalysis by enzymes. None, at all events, have been shown to exist. Moreover, such an explanation is of very rare application to catalysis of any kind. The hypothesis of the action of enzymes which is most in agreement with all the facts known at present may be stated somewhat as follows: the molecules which are to enter into reaction are condensed by adsorption on the surface of the colloidal particles of the enzyme and their final state of equilibrium is brought about at a greatly accelerated rate. Whether, as Faraday seems to hold, the close approximation, and high concentration, is in itself sufficient to account, by mass action, for the increased rate of reaction is a matter for future investigation. It may well be, as Hardy points out (Proc. Roy. Soc., vol. lxxxviii. B, pp. 174 and 175), that it is in the actual process of condensation itself that the molecules are subject to stresses which result in exceptional chemical activity; their chemical potential may very well be raised in the process. It appears to be a phenomenon of very general occurrence that it is in the very act of change of state that special activities are manifested. This is particularly obvious in living organisms, where a system in equilibrium is dead, but it applies also to non-vital systems.

I would finally point out that it should not be stated that the action of enzymes does not obey mass action. Mass action is universal in its application; but, in heterogeneous systems it is controlled by other factors, such as diffusion and surface adsorption, the latter factor playing the chief part in the velocity of reaction in micro-heterogeneous systems, such as those of colloids. The rate of the reaction is conditioned by the relative masses of the molecules condensed on the surface at any one moment of time. It will be seen that the difficulty of applying the law of mass action consists in the determination of the real active masses. W. M. BAYLISS.

Institute of Physiology, University College,
Gower Street, W.C.

Tidal Friction and Ice Ages.

A CAREFUL study of the conditions of land height during the earlier stages of the Quaternary glacial period seems to show that the earth was then less oblate, i.e. the north and south polar regions stood higher than now, to the extent of as much as 10,000 ft. in places, while the equatorial regions stood lower, by

some 500 ft. The spreading of ice-sheets from these high lands may well have been the initial cause of the cooling which produced the Glacial epoch.

Going further back in geological time, we find, as is well known, a series of long periods of epeirogenetic movement alternating with long periods of marine transgression. The last great change seems to have been continuous from Carboniferous times, with a girdle of land round the equator high enough to be heavily glaciated, through Mesozoic times, with a marine transgression, to Pliocene times, when the high land emerged at the poles.

Qualitatively, at least, it seems possible to read the late Sir G. H. Darwin's theory of tidal friction into these changes. By that theory, owing to the differential attraction of the moon on the tidal protuberances, the rotational momentum of the earth is gradually decreasing. This decrease may manifest itself in two ways, either by an actual decrease in the rotational velocity, or by a decrease in oblateness, i.e. by a movement of matter towards the poles.

It is probable that the earth's crust has a certain tendency to slide on its nucleus, and since the effect of tidal friction is chiefly felt in the crust, while the bulk of the momentum must lie in the heavy nucleus, it follows that the effect of tidal friction must be to tend to slide the crust round the nucleus parallel with the equator. As the crust must vary both in thickness and in the closeness with which it is attached to the nucleus, this means a thrust against the deeper and more closely attached portions. The thrust would tend to force some of the crust poleward on either side from the equator, i.e. to decrease the equatorial bulge.

But the friction between crust and nucleus is very great, and must in time result in an appreciable decrease in the angular velocity of the latter. Probably the action takes place in alternating stepsperiods of constant rotational velocity, combined with a gradual thrusting of the crust poleward from the equator, alternating with periods of stability of the crust and gradual decrease in the rotational velocity. The former are periods of earth movement, mountain forming, and disturbance, resulting in the gradual deepening of the ocean over the equator and emergence at the poles; the latter are associated with a slow retirement of the ocean towards the poles, resulting in marine transgressions in middle and higher latitudes.

I have been able to accumulate a great deal of evidence which supports the theory I have outlined above on the geological side. I am, however, not sufficiently a mathematician to be able to satisfy myself that the cause, tidal friction, is commensurable with the effects, and I am begging the publicity of your columns to ask if someone better situated will help me in that respect. C. E. P. BROOKS.

Homeleigh," 3 Roseleigh Avenue,

Highbury, N., October 10.

Ar the Editor's request I contribute a few remarks on Mr. Brooks's letter. The suggestion that tidal friction might be a cause of changes in the distribution of land and water is not new. It will be found in a "Note" in NATURE of April 25, 1889 (vol. xxxix., p. 613), where it is attributed to M. A. Blytt; and that may not be its first appearance. The character of the changes is that indicated by Mr. Brooks, but the mechanism by which they are effected is a little different. The hypothesis of a crust riding more or less freely on a nucleus is unnecessary, and difficult to reconcile with well-established results. Again, the frictional stresses do not operate directly to cause a flow of material towards or away from the poles, but indirectly by diminishing the speed of rotation.

The mechanical process may be followed very easily

without any mathematics. The surface of the ocean, apart from waves and tides, is at any time a figure of equilibrium answering to the speed of rotation at the time, more oblate when the speed is greater, less oblate when it is slower. Let us imagine that the lithosphere also is at some time a figure of equilibrium answering to the speed of rotation at that time. If the speed remained constant, the lithosphere would retain this figure, and the matter within it would remain always in the same configuration without having to support any internal tangential stress. Now suppose that the speed of rotation gradually diminishes. The surface of the ocean will gradually become less and less oblate. The lithosphere also will gradually become less oblate, but not to such an extent as to make it a figure of equilibrium answering to the diminished speed of rotation, while the matter within it will get into a state of gradually increasing internal tangential stress. The effect on the distribution of land and water will be that the depth of the ocean will gradually diminish in lower latitudes and increase in higher latitudes, the latitudes of no change being 35° 16' N. and S.

The internal tangential stress in the matter within the lithosphere may increase so much that it can no longer be supported. If this happens a series of local fractures will take place, continuing until the lithosphere is again adjusted much more nearly to a figure of equilibrium, which will be less oblate than the original figure. The effect on the distribution of land and water will be that the depth of the ocean will increase rather rapidly and spasmodically in lower latitudes and diminish in higher latitudes.

Accordingly the kind of geological change which the theory of tidal friction would lead us to expect is a sort of rhythmic sequence, involving long periods of comparative quiescence, marked by what Suess calls "positive movements of the strand," in the higher latitudes, and negative movements" in the lower, alternating witih comparatively short periods of greater activity, marked by rise of the land around the poles and subsidences in the equatorial regions. It is for geologists to say whether the facts known to them are consistent with this description or not. A. E. H. Love.

The Age of a Herring.

IN the issue of NATURE for September 17 Prof. D'Arcy Thompson states that he is unable to persuade himself of the validity of Dr. Hjort's conclusions based upon the methods of determining the age of herrings by a study of their scale-rings.

It is, of course, impossible to attempt to deal in a few words with all the evidence brought forward in favour of these methods in recent years by different biologists, and we must, with regard to the herring, refer to our published papers,1 where arguments are given in favour of the primary assumption that the age of a herring may be determined by counting the rings seen on its scales. The facts supporting this assumption are briefly :

(1) For young individuals (up to age of three years) the results of age determinations by means of the scale-rings correspond with the results obtained by

1 Hjort, "Report on Herring Investigations until January, 1910," Publ. de Circonst., No. 53. Copenhagen, 1910.

Hjort and Lea, "Some Results of the Internat. Herring Inv., 1907-11. Publ. de Circonst., No. 61. Copenhagen, 1911.

Hjort, Fluctuations in the Great Fisheries of Northern Europe," Rapports et Procès-Verbaux, vol. xx. Copenhagen, 1914.

Lea, "On the Methods used in the Herring Investigations," Publ. de Circonst., No. 53 Copenhagen, 1910.

Lea, "A Study on the Growth of Herrings." Publ. de Circonst., No. 61. Copenhagen, 1911.

Lea," Further Studies concerning the Methods of calculating the Growth of Herrings," Publ. de Circonst., No. 66. Copenhagen, 1913.

plotting frequency curves for the length measurements of the individuals.

(2) Scale examination of small herrings continued with short intervals during all seasons showed that the formation of the so-called winter rings took place during the winter, while the formation of the so-called summer belts commenced in the spring and continued during the summer months. That the summer belt is small at the commencement of the formation in May, while it is large on the completion of the formation in the beginning of autumn, has been proved by observations carried on during four years. Regarding the older fish, it has been difficult to proceed in the same manner as for younger fish, as the frequency curves fail to give any hints as to the age groups represented in a sample, while, on the other hand, the fishing season for the old herrings does not extend over all seasons of the year. The following facts point to the correctness of the assumption that the conditions here are strictly homologous to the conditions as regards the younger fish.

(3) Among the Norwegian herrings a great many

3 4

6 7

10 11 12 13 14 15 16 17 18 FIG 1.-Showing the captures of Norwegian mature herrings for eight successive years, arranged in percentage frequency curves according to the number of rings on the scales (the numbers along the abscissa denoting the ring groups).

individuals had an abnormally small third summer belt on their scales. Herrings showing this abnormality have been very frequently observed during all the years from 1907 to 1914, but while the scales of these herrings in the year 1907 had only one summer belt outside the abnormal one in 1908, they showed two summer belts, and so on until the winter 1913-14, when they had seven summer belts outside. Thus these herrings, so easily distinguishable by their abnormality, have during the seven years of observation annually formed one summer belt on their scales, each belt being separated by a winter ring from the preceding and succeeding belts.

(4) By scale investigations on the Norwegian spring herrings (spawning herrings), carried out during the years from 1907 to 1914, results are obtained the main points of which are given in Fig. 1. This diagram is based upon all the material from 1907-13, while for 1914 part of the material was not worked up when the diagram was constructed (still the curve for this year is based upon more than 2000 individuals).

part of a flame, must have great influence over the combinations there taking place" (656). The last sentence is interesting in connection with the work of Prof. Bone on surface combustion.

Institute of Physiology, University College,
Gower Street, W.C.

Tidal Friction and Ice Ages.

some 500 ft. The spreading of ice-sheets from these high lands may well have been the initial cause of the cooling which produced the Glacial epoch.

I have been able to accumulate a great deal of evidence which supports the theory I have outlined above on the geological side. I am, however, not sufficiently a mathematician to be able to satisiy myself that the cause, tidal friction, is commensurable with the effects, and I am begging the publicity of your columns to ask if someone better situated will help me in that respect. C. E. P. BROOKS.

Homeleigh," 3 Roseleigh Avenue,

Highbury, N., October 10.

AT the Editor's request I contribute a few remarks Mr. Brooks's letter. The suggestion that tida friction might be a cause of changes in the distribution of land and water is not new. It will be found in a "Note in NATURE of April 25, 1889 (vol. xxxix., p. 613), where it is attributed to M. A. Blytt; and that may not be its first appearance. The character of the changes is that indicated by Mr. Brooks, but the mechanism by which they are effected is a little different. The hypothesis of a crust riding more or less freely on a nucleus is unnecessary, and difficult to reconcile with well-established results. Again, the frictional stresses do not operate directly to cause a flow of material towards or away from the poles, but indirectly by diminishing the speed of rotation.

The mechanical process may be followed very easily

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