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precautions to prevent experimental errors are often given in considerable detail, as, for example, in regard to freezing-point determinations and conductivity measurements; yet if this be the intention of these descriptions they are singularly incomplete in other respects. For example, in describing the dete. nination of the freezing point the only thing said about the thermometer to be used is that it may have either a fixed or a variable zero. We venture to think that some description of the Beckmann thermometer and the method of using it would have been of service here. BENJAMIN MOORE.

THE MAKING OF ROCKS. Petrogenesis. By Dr. C. Doelter. Pp. xii+262. (Brunswick Vieweg und Sohn, 1906.) Price 7 marks.

IN

N this work, which would be valued highly for its references to current literature alone, the author brings together what is known as to the origin of various types of rocks. Its outlook is that of the mineralogist and not of the physical geographer; but this enables the author, though far too modestly, to bring his researches on the construction of minerals and rocks to bear upon broad geological problems. As a treatise, the book is elementary and yet satisfying; in the series of which it forms a part, "Sammlung naturwissenschaftlicher und mathematischer Monographien," it exactly fills its place as an exposition of prevalent, if not necessarily established, views. Very often these views are subjected to criticism that shows how far we are from finality and conclusions; but the lucidity of discussion and absence of bias displayed by Dr. Doelter make us grateful to him as a guide. The history of the struggle for the Rhine in no way affects his scientific judgment; and once again we feel that Austria holds the balance in the geological controversies of our time.

When we say that the book is elementary, we mean this in the best of senses. It goes to the root of a question, and compels the reader to understand it. As an example of the large amount of valuable matter that may be compressed into one paragraph, we may take the following (p. 80), from a discussion on differentiation in igneous magmas :

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Attempts have been made, as we have seen, to connect differentiation fundamentally with the existence of magmas which will not mix with one another. But this is an improbable supposition, since every magma can dissolve any other, as I have shown experimentally. The solubility of one mineral in another depends only on the temperature; and at a temperature varying with each case, the critical temperature of solution, the products of fusion are soluble in one another. Experiment also proves to us that no separation takes place in the fluids so long as they are stirred; it occurs first as cooling goes on; where there is no movement, separation can take place according to specific gravity, even in the fluid state."

The book opens with a discussion of the causes of fluidity of magmas within the earth, and their occasional appearance at the surface is attributed

primarily to tectonic movements. When relief from pressure comes, the magma becomes fluid, and corrodes the surrounding rocks. The gases contained in it operate "like a blowpipe-flame." The results of such corrosion are treated later (p. 116, &c.), and Dr. Doelter remarks, following Daly's recent papers, that basic lavas, coming quickly up broad cracks, reach us in a state of greater purity than acid ones, which move more slowly, and have greater opportunities for affecting the walls that bound them. The acid masses "exhibit traces of the country-rocks, but not necessarily near the contact-zone, since, in the case of deep-seated rocks, the absorbed fragments may become distributed in the interior of the mass."

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The author's remarks on the potency of mineralising agents during the consolidation of igneous rocks are based upon his own well-known experiments. Mica thus seems always to require the presence of fluorine. While water is the greatest mineraliser, we are reminded that we are not dealing with pure water in the earth, but with water containing chlorides, hydrochloric acid, boric acid, and so forth (p. 24). Certain minerals decompose in their own products of fusion, and give rise to other minerals, or mere glass, on consolidation. In such cases, the crystalline condition remains stable only at a lower temperature than that of fusion, and the function of a mineraliser or crystalliser" is to reduce the temperature at which the substance crystallises out again. If the right point is reached, the original mineral is recovered in its crystalline form. Thus, in the muchdebated case of quartz, the mineral, at ordinary pressure, will not separate from its product of fusion at temperatures above 950°. Below this temperature its crystals are stable. Above it they are unstable, although their melting-point is not reached until 1600° or 1700°. The common minerals that require the help of mineralisers for their formation are albite, orthoclase, quartz, garnet, haüyne, epidote, wollastonite, hornblende, and mica. Hence an acid crystal. line rock cannot arise without mineralisers, and the frequent presence of tourmaline, fluorspar, scheelite, and so forth, in granite, indicating boric acid, fluorine, tungstic acid, chlorides, &c., bears out in nature the results of synthetic laboratory work.

On p. 65 it is interestingly pointed out that the different items in the chemical analysis of a rock, as written down, possess very different values, and that too large deductions must not be based on small differences in the quantities of magnesia, soda, or potash stated to be present. Exactitude in these determinations is not obtainable with the same degree of success as in the case of silica and alumina, and the alkalies, unfortunately, usually appear as small numbers, in which the second place of decimals becomes of importance for comparison. The American school, by the by, has made such headway that the word "salisch" slips in naturally on p. 44.

We cannot dwell on all the important considerations here put forward as to the processes that go on during the cooling of igneous rocks. Among these, the description of "Unterkühlung" on p. 137 strikes us as of especial interest. The retention of

a mineral in a state of fusion below its ordinary melting-point may allow of the previous crystallisation of another, which cannot sustain such conditions, and thus the normal order of crystallisation may be reversed. This fact is used to explain the crystallisation of augite before the felspar in basic rocks, which, in normal circumstances, so frequently show ophitic structure.

All through the book the influence of personal experiment remains manifest, and we must not complain if the genesis of the sedimentary rocks is treated in a somewhat rapid fashion. Flints thus receive far less than their due (p. 232), considering how much they have been discussed. Guppy's observations on silicified corals in the Fiji Islands raise, for instance, new questions in themselves. But references to recent work, such as Linck's on the separation of calcium carbonate from sea-water, will lead the reader for ward; and we turn back contentedly from these scantier pages to the fine account of the problems of contact-metamorphism, and thank the author again and again for his clear and stimulating treatise.

As is natural in so wide a field, we miss mention of some memorable work, such as that of Harker on mixed rocks in the Inner Hebrides; on the other hand, we hail with delight the name of MacGregory (p. 31), who appears to be Prof. J. W. Gregory in the glory of a Scottish title. GRENVILLE A. J. COLE.

STRUCTURES AND MATERIALS.

Theory of Structures and Strength of Materials. By Prof. Henry T. Bovey. Fourth edition. Pp. xiii+ 968. (New York: John Wiley and Sons; London : Chapman and Hall, 1905.) Price 1. 118. 6d. net.

THIS

HIS well-known text-book has been largely rewritten and enlarged for the present fourth edition. In the preface Prof. Bovey states that a number of fresh examples, mostly drawn from actual practice, have been added to the various chapters, and that all tables of strengths, elasticities, and weights of materials have been brought up to date.

In chap. i. a description of Bow's method of notation is given, and the author has now adopted this system throughout the book when dealing with stresses developed in framed structures. The treatment of the three-hinged braced arch for station roofs and for sheds of wide span is a new piece of work in this chapter. In chap. ii. there is a new series of paragraphs dealing with the graphical determination of the maximum bending moment at any point of an arbitrarily loaded girder, and several examples illustrating the author's methods are worked

the older editions, which dealt with thick-walled, hollow cylinders, has now been incorporated into chap. v., which treats of the more difficult work on stress and strain, and undoubtedly it follows more naturally in this position after the discussion of the general equations of stress.

In chap. vii., in dealing with the relation of the neutral plane to the stress at any point in a beam, Prof. Bovey has incorporated the results of his own experimental work, which was carried out with the view of determining within the limits of elasticity the changes of fibre length at different depths of a beam when loaded transversely. In this chapter there are also additional paragraphs dealing with the design of reinforced concrete beams, the position of the neutral axis, and the strength of such beams; additional graphical methods are given for determining the slope and deflection in loaded beams, and in connection with the theory of continuous girders fresh matter has been introduced.

In chap. viii., which deals with the theory and the bending of struts, the results of the most recent experiments have been incorporated, and, as the chapter has been rearranged, it is now much more useful to engineers engaged in the difficult problem of strut design. In chap. ix. the stresses in non-circular shafts are discussed, and there is also much new matter in the paragraphs on the efficiency of shafting and the whirling of shafting, and open coil springs are dealt with, as well as the ordinary helical springs. Chap. x., which is devoted to bridges, has methods are used throughout for the determination been entirely rewritten and greatly improved. Graphical of stresses in the piers, and the most recent types of bridges are discussed and explained. Excellent tables are given of the loads upon, and the weights of, bridges, and several examples of fairly large bridges are worked out in complete detail. This chapter is now a most valuable one for those who are concerned with the design of bridges of all classes, and the examples have been made thoroughly practical. We have no hesitation in saying that Prof. Bovey in thus practically rewriting his book has considerably improved its value both to the engineering student and to the civil engineer engaged in the design of all classes of structures in steel and iron.

T. H. B.

RATIONAL DAIRYING. Dairy Chemistry. By Harry Snyder. Pp. x+190. (London: Macmillan and Co., Ltd.; New York: The Macmillan Co., 1906.) Price 4s. 6d. net.

out in full. Chap. iii. of the older editions has wisely PROF. SNYDER'S work as agricultural chemist

been broken up into two chapters, one (chap. iii.) dealing with momentum, energy, and balancing, and the other (chap. iv.) with stress, strain, and elasticity. In the older editions this chapter was a very difficult one for the student to follow, and the author, in rewriting and dividing it, has brought the various steps of the work into their true relation one with the other. The whole of the material in chap. x. of

in the University of Minnesota is well known. This State, with a population less than that of Kent and Essex, possesses a University Agricultural Department in which are 800 students most of whom are attending a three years' course. The majority are students who during the summer months have to work for a living, and at the close of their academic training return to rural employment. Thus Min

nesota, in common with other States of the Middle West, is year by year producing an army of workers who have learnt to base their work on scientific principles and to look to the results of scientific research for the future development of their industry.

The success of the American agricultural colleges in turning out trained craftsmen (they are not, perhaps, equally successful in producing highly-trained scientific experts) is to be traced to the intimate association of the practical and the scientific teaching. On the one hand science is taught, but the mind of the student is constantly being directed to its industrial applications; on the other hand the industry is taught, but with constant reference to underlying scientific principles. Prof. Snyder's book is a capital example of the method of industrial teaching. It is a text-book of dairying, but there is no rule-ofthumb; an appeal is made to reason; processes are advocated because found by experiment to be sound; the impression left on the student's mind is, "This is the best to-day; there may be a better to-morrow.' To take from the book two examples of the effect of this method of training on industrial development :-The advantages of the cold curing of Cheddar cheese were established by Babcock and Russell at the Wisconsin Experiment Station. It is a rational process based on recent investigations on the action of the natural enzymes in milk. The results were only published in 1901, but already cold-curing factories have risen throughout Ontario and the cheeseproducing States of the Union, showing a readiness to accept the results of scientific investigation, although involving a large capital outlay, to which it is difficult to find a parallel in British agriculture. As the second illustration, take the percentage of fat and total solids in milk, 3 and 12 respectively, enforced as the legal standard in Minnesota. To obtain such milk, cattle must be bred up to this high standard. The agricultural community is far-sighted enough to see that, although it may involve hardship on individuals, the high standard is an advantage to a State where butter and cheese production is an important industry.

The book should prove almost as useful to dairymen in this country as in America. There are few Americanisms either in spelling or phraseology, and throughout there is an insistence on the importance of proper hygienic conditions in dairying, with several useful suggestions as to how cleanliness can be secured, which should be invaluable, for it is on account of the neglect of such conditions in this country that dairymen's troubles are generally due. The method of calculating dividends in dairying is also worthy of particular attention here. There are, unfortunately, a few misprints and inaccuracies, together with curious repetitions of the same statements, suggesting that the book has been edited from lecture notes compiled in card-catalogue form. As usual in American works, the whole of the nitrogen compounds in foods are considered as proteids. The bibliography containing references to American, German, and British scientific papers is an excellent feature.

T. S. D.

OUR BOOK SHELF.

Gedanken über Vererbung. Dr. Alexander Petrunkewitsch. Pp. 83. (Freiburg, i. B.: Speyer and Kaerner, 1904.) Price 1.80 marks.

THE author thinks that clearness is gained if we regard the organism as a continually changing mechanical system with a life-cycle extending from the arbitrarily chosen moment of oogenesis to the post-mortem death of the last scrap of decaying tissue. An acquired character is the result of a reaction of the system to external influences, and presupposes a definite heritable structure capable of reacting, so that there is no sharp boundary between acquired and inherited be due to a coincidence of successive reactions. The characters. What is called a heritable character may concept of heredity strictly applies only to the germ. cells; it is simply "the process which leads to the formation of germ-cells whose structure is the same as or like the parental germ-cells." Development is the expression of this structure, and the formative causes of development lie in the relation between the system and its environment. An animate system can only exist in definite conditions, which can only oscillate within definite limits. Life is an adjustment between the amplitudes of variation in the animate system and in the environment, and involves a progressive limitation of the organismal variability. Those variations the causes of which lie in the oscillations of the germ-cell structure may be called gametogenous or endogenous as contrasted with exogenous variations (modifications) which are acquired in the course of life. This distinction will hold even if we abandon the theory of the continuity of the germ-plasm, and simply suppose that the germhave attained the same structure as the parental germcells are those cells which through chemical reactions cells. When this sameness is not attained variations result, the amplitude of which may be trivial or fatal, or it may be that a new pattern of system results which we call a mutation. So far as we can see, the author simply re-states familiar facts and ideas in a slightly novel way, and we do not share his confidence that clearness is gained by so doing.

J. A. T.

Giordano Bruno. In Memoriam of the 17th February, 1600. By Alois Riehl. Translated by Agnes Fry. Pp. 112. (Edinburgh and London: T. Ñ. Foulis, 1905.) Price 2s. 6d. net.

THE life of Giordano Bruno is not altogether unfamiliar to readers of reviews in NATURE. A larger volume on this subject was reviewed about two years ago (March 31, 1904, vol. xix., p. 505). Still earlier, in May, 1900, the original of the present translation was reviewed, and the reviewer expressed the wish that Prof. Alois Riehl's essay could be presented in English. This suggestion has led to the appearance of the present volume.

The first account of Giordano Bruno coming from the pen of Prof. Alois Riehl dates from 1889, the year in which the present monument was erected to Bruno on the site of his martyrdom. The tercentenary of Bruno's death on February 17, 1900, formed the occasion for a second edition, in which the account of Bruno's philosophy was revised. Without entering into minute detail, the present translation bears the impress of being a good one, and when the small size of the book is taken into account the description of Bruno's life will be found to be as full and complete as could be possibly expected.

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.]

Geological Survey of Canada.

Is the issue of NATURE of June 21 is a letter from Mr. A. P. Low. This communication is liable to be misleading, and I shall be greatly obliged if you will allow me to correct the misstatement which it contain, namely, that "at the same time, Dr. R. Bell simply returned to his former position of assistant-director and chief geologist, to which he had been appointed in 1892."

I was not appointed chief geologist in 1892. This office did not then exist. It was created on March 27 last, and I was appointed to it by a formal Order-in-Council on that date, a large increase being made to my salary at the same time. ROBERT BELL.

Office of the Canadian High Commissioner, London,
July 9.

I HAVE taken some trouble to inquire into the extraordinary appointment to the Geological Survey of Canada concerning which you published a paragraph on April 26 (vol. xxiii., p. 613) and a letter on June 21 (p. 175). I send you my results in case you would care to continue the correspondence.

Report states that the Premier informed Dr. Bell that the Government, for its own reasons, was going to make certain changes in the administration of the department, but that wishing Dr. Bell to be quite contented with these changes, he asked him to state the conditions which would be agreeable to him. I have also learned that the Premier transferred Dr. Bell's letter for action to the Minister of the Interior, who is at the head of the Geological Survey Department. Owing to the great pressure of the business of the session of Parliament, the matter has not yet been considered, and further changes are probable, but for the present Dr. Bell has been promoted to be chief geologist of Canada, and allowed to devote his time entirely to scientific matters. He attains at least equal rank, and receives a substantial addition to his salary, with a promise of further increase in the near future. In connection with the above change, Sir Wilfrid Laurier spoke in Parliament in the highest terms of Dr. Bell's ability and of the great scientific services he had already rendered the Dominion.

If these are facts, then Mr. Low's letter (p. 175) appears to be inaccurate. The office of chief geologist was, it seems, newly created for Dr. Bell last March, and he was not appointed to it, as Mr. Low asserts, in 1892.

Mr. Low, I find, is quite unknown in the geological world, whereas Dr. Robert Bell's name has long been familiar throughout Europe and America. He is now in his fiftieth year of service to the Government of Canada in connection with its Geological Survey, and as practical head of that department for the last five years he has maintained its high reputation and administered, all its affairs with credit. He is a Fellow of the Royal Society of London, a Doctor of Science of Cambridge, a Doctor of Medicine of McGill, a Doctor of Laws, &c., and has been honoured by the King with the companionship of the Imperial Service Order.

During his administration of the business affairs of the Canadian Survey, it is generally recognised that he has improved its efficiency in many ways, and has increased the number of its officers, the extent of its operations, the Government grant, the library, the extent of its premises, &c. He has sent to the field an average of more than thirty parties every year, as compared with less than half that number in the time of his various predecessors. Surely this is a good record, for the sooner a country is surveyed the better it is for all economic purposes.

The above matters and many others are clearly described by Dr. Bell in his annual summary reports of the survey for the past five years. He had previously caused

to be carried on very extensive topographical surveys in all sections of the vast Dominion, taking the leading part himself in this work. It was for these valuable services to geography that the Royal Geographical Society this year awarded him the patron's gold medal, with the approval of the King.

It is clear, I think, that although the interests of science have not been wholly sacrificed, party politics and not geology have been in question in regard to Mr. Low's appointment. F. R. S. July 7.

Osmotic Pressure.

THE gravamen of our criticism of Prof. Kahlenberg's paper is directed against his statement that "indirect measurements of osmotic pressures involve the assumption that the gas laws hold for solutions." In vol. lxxvii., Proc. Roy. Soc., we deduce a relation between the osmotic and vapour pressures of a solution which is independent of the gas laws "holding for solutions." Prof. Kahlenberg, in his recent letter, does not attempt to show that this relation is unsound; we may therefore take it that he accepts the theory, but is dissatisfied with the experimental evidence which we adduced to corroborate it. Perhaps the following will help to convince him.

In a paper read before the Royal Society, June 7, we give the results of the direct and indirect measurements of the osmotic pressures of some aqueous solutions of cane sugar.

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Since reading this paper we have found that aqueous solutions of dextrose and galactose give similarly concordant results. As regards the last paragraph of Prof. Kahlenberg's letter (p. 222), we would point out that he gives no experimental evidence for the assumption that the sugar that had passed through the rubber membrane was sugar from which, so to speak, the solvent had been filtered off. Until such evidence is forthcoming, it seems to us that the criticism we levelled at his work is legitimate, and suggests a simple explanation of the low BERKELEY.

results he obtained.

Foxcombe, near Oxford.

E. G. J. HARTLEY.

Family Diseases and Temperaments. MAY I appeal through your columns to those of your readers who are interested in the tendency of certain diseases and temperaments to run in particular families to aid me in an investigation I am at present making? The schedules now being issued contain space for a great deal of information, but it is rare for any single recorder to be able to supply all of it. What is wanted is a perfectly frank statement of what the recorder knows or can find out without much trouble. The only request made is that if the recorder feels unable to state certain facts not to the family credit, as well as those which indicate a sound, successful stock, no attempt should be made to fill in the schedule. At the same time, no names are required, the recorder may select any family he pleases for record, and the name of the recorder is only required in case it is needful to ask for explanation of any entry, and as a general sign of good faith.

I am fully aware of the labour involved in giving a fairly full family record, and my gratitude for aid in the matter is very great. At the same time, it is, I think, not unjustifiable to hope that among the readers of NATURE there will be some ready to help in an inquiry which if completed will be of considerable scientific value. There exists at present no ample data from which we can determine the inter-relationship of disease, temperament, and success in life. We know comparatively little the extent to which these factors are associated together or persist in certain families. After some considerable labour, about 200 records have been obtained, some of them very full and excellent, and the majority of considerable value. But the

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IN applying the principles of thermodynamics to diffusion of gases, several pitfalls have to be guarded against.

In the first place, if we adopt the old definition of

entropy in terms of integrals of the form Jao/T, we are

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almost certain to go wrong when we come to deal with diffusion. If we imagine diffusion to take place between two of the ideal perfect gases of our text-books at constant pressure, volume and temperature, and without gain or loss of heat, no quantity of the nature of do appears to be associated with the phenomenon, and it is easy to rush to the conclusion that no change of entropy takes place. This danger is avoided if we adopt Mr. Swinburne's plan of defining entropy in terms of waste or unavailable energy relative to an assumed auxiliary medium. By auxiliary medium" is here meant a medium at uniform temperature T, which can be used indefinitely as a refrigerator in thermodynamic operations, and any change in the amount of unavailable energy under such conditions, when divided by the temperature T, gives the corresponding change of entropy.

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If this definition is adopted we see that the phenomenon of mixing the gases does not in itself suffice to determine the changes of entropy associated with it. The matter can only be decided by an appeal to experience as to the means whereby the gases can be separated or mixed reversibly. The case of an ideal perfect gas "forms no exception to this statement.

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The proper inference is, not that the diffusion involves no change of entropy, but that the change of entropy, if it exist, cannot be expressed as a sum of differentials of the form dQ/T.

The second pitfall occurs when we take the well-known expression for the entropy of a perfect gas in terms of pressure (or volume) and temperature, and try by this means to connect the entropy of the mixture with the entropies of the components. Where we are likely to get into trouble is by ignoring the integration constants in the expressions for the entropy. There is no evidence from mere thermodynamic reasoning that the constant does not change in the process of diffusion. All we can infer is that the change of entropy associated with the mixing of gases at uniform pressure and temperature is constant, i.e. independent of pressure and temperature.

To sum up, then, even when we have defined an ideal perfect gas in the ordinary way, and assumed the property that two such gases can mix in a closed vessel without change of pressure and temperature, thermodynamical considerations still give us no information whatever as to the change of entropy accompanying diffusion, and on this point a further appeal to experience is necessary.

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This amounts to saying that our definition of perfect gases is still incomplete. What further property shall we assume in order to complete it? If we regard a perfect gas as a mere invention on paper, the most useful plan is to take some simple property which is approximately satisfied in the case of actual gases and assume that this property is accurately satisfied by our perfect gases. Now, actual gases may be separated and re-mixed either by diffusion through a membrane or by liquefying, or, if preferred, freezing one of the constituents.

Taking either of these processes, and making suitable assumptions which would render that process perfectly reversible, we are led to the inference that the whole entropy of a mixture of perfect gases should be taken to be equal to the sum of the whole entropies of its components at the same temperature and partial pressure, i.e. if each component occupied the same volume as the final mixture.

According to this view, when diffusion takes place at

constant temperature and pressure, there is a gain of entropy and a loss of available energy equal in amount to that which would be incurred if each of the constituents were to expand by rushing into a vacuum until it occupied the same volume as the final mixture.

There is another way of partially separating the constituents of a gas mixture. If the mixture be introduced into a field of force such as that due to the earth's attraction, or if we imagine it to be whirled in a centrifuge, the denser gases will predominate in the lower parts of the atmosphere or where the potential is greatest, and the lighter gases will predominate in the upper regions or where the potential is least. In this case the partial separation is effected at the expense of work done by the field of force.

This note does not purport to deal in full detail with the thermodynamics of diffusion, but merely to direct attention to certain points which are easily overlooked. One of the most important of these points is that the possibility of producing mechanical work by the diffusion of gases through a membrane at constant temperature is not necessarily inconsistent with the principles of thermodynamics or the ordinary definitions of a perfect gas.

If any physicist should claim to have discovered Maxwell's demons in connection with the diffusion of gases, the first questions we should ask him are:

(1) Can he, without the performance of external work, separate the gases in a mixture in such a way that the temperature is the same at the end as at the beginning, and the separated constituents each occupy volumes smaller than that of the original mixture?

(2) Can he obtain external work by the mixing of two gases without change of temperature if the initial volume of each gas is not less than the final volume of the mixture?

(3) Are his claims based on new experimental evidence? G. H. BRYAN.

Early Meteors of the Perseid Shower. THE moon being new on July 21 this year renders the conditions favourable for observing the earlier members of the great Perseid display. A few of these are usually visible on July 15, and probably just before that night, and it would be interesting if multiple observations of supposed Perseids could be obtained so that their radiants might be definitely assigned without the risk of error,

A single record of a meteor-flight only permits an assumption to be made as to the apparent radiant, and mistakes frequently result. For example, if a streakleaving meteor, seen at the July-August epoch, happens to be directed from the northern part of Perseus it will certainly be attributed to the Perseid swarm, though it may quite possibly have had its origin in a different shower from Cassiopeia, Andromeda, Aries, Camelopardus or Auriga. To avoid such errors of allocation it is proposed to maintain simultaneous watches this year between July 15 and 28 from 10 to 12 p.m., and the writer would be glad to hear particulars of any observations for comparison with similar results obtained at Bristol.

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The mean height of the Perseid meteors has already been satisfactorily deduced, but it seems desirable further to investigate the position and motion of the radiant, especially during the last half of July. Such meteors as amongst the stars of Perseus or bordering constellations art the best for indicating the exact place of the radiant, and bright meteors should always be carefully registered, as they are very likely to have been noticed elsewhere. The centre of radiation travels from near Andromeda at the middle of July to a few degrees south of the starcluster at x Persei at the end, the ephemeris places (Monthly Notices, lxii., 169) being as under :

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