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designing a piece of apparatus which he calls the optical disc"; this, at a moment's notice, can be adjusted so as to show the path of the rays in any one of the important cases usually dealt with in elementary lectures on geometrical optics. The reflection of a single ray, or a number of rays (parallel or divergent) from a plane, concave, or convex mirror; the refraction of a ray at a plane surface, including the case where total internal reflection occurs; the path of a single ray or a number of rays through a convergent or a divergent lens; the nature of spherical and chromatic aberration; the theory of the rainbow, these are a few of the experiments which can be performed by its aid. The apparatus, which is sold by Messrs. A. Gallenkamp and Co., Ltd., is very compact, and its general arrangement is so good that one experiment may be changed for another in about half a minute. The same firm supplies an appliance comprising bent glass rods, which show the total reflection phenomena generally demonstrated by the aid of the illuminated fountain; a simple polarising apparatus, consisting of a pile of plates and a black glass reflector, which may be attached to the optical disc described above; and a simple form of polariscope, together with specimens of strained glass showing the characteristic coloured figures associated with double refraction.

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AN interesting light is thrown on the difficult problem of the behaviour of manures in soils by some recent observations, made under the auspices of the Bureau of Soils of the United States Department of Agriculture, by Messrs. Oswald Schreiner and George H. Failyer, and published in the form of two communications in the Journal of Physical Chemistry (Nos. 4 and 5). these deals with the absorption by different soils of the phosphates of calcium and sodium from dilute solutions, whilst in the other the removal by a soil of potassium from an aqueous solution of potassium chloride is studied. It is shown that the soils dealt with take up the phosphates and potassium from aqueous solution according to the law of a monomolecular reaction, and that the action is strictly reversible. Water washes out the absorbed material according to a similar law. Each soil is characterised by a definite limiting capacity of absorption, which differs with different soils. It is remarkable that for certain clay soils and clay loams this capacity is the same for sodium phosphate as for calcium phosphate, pointing to the occurrence of definite reversible chemical actions.

It is particularly noteworthy that when water percolates through a soil the amounts of phosphate or of potassium in the transmitted liquid give no clue to the quantities of these materials present in the soil itself. The results are determined, not by solubility alone, but by a special law governing the removal of the absorbed substances.

The Institute of Chemistry has published a List of Official Chemical Appointments held in Great Britain and Ireland, in India and the Colonies." The list has been compiled under the supervision of the proceedings committee of the institute by Mr. R. B. Pilcher, the secretary of the institute, and its price is 25. net. The list is arranged in two main divisions; the first contains appointmments under the departments of State and professorial appointments in the British Isles; the second section deals similarly with India and the colonies. The information provided indicates the steadily increasing demand for professional chemical services in connection with State and municipal administration, and it should prove of service to chemists everywhere.

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The brightness of the comet when discovered in 1886 is taken as 1.0.

The observation of this comet at Heidelberg on July 16 gave corrections of 12m. IIS. and -1° 37'5 to this ephemeris, and thereby brought the calculated time of perihelion to about September 8.35, 1906 (Paris M.T.). Applying these corrections to the above ephemeris, it will be seen that the comet will be about 3° north of Mira Ceti on August 4.

AN UNEXPLAINED OBSERVATION.-In No. 4106 of the Astronomische Nachrichten Prof. Barnard places on record the following observation, which he made so far back as August 13, 1892, and for which he has not yet been able to find any explanation. While examining Venus with the 36-inch Lick refractor at oh. 50m. (G.M.T.) on August 13, 1892, he saw a star of about the seventh magnitude in the same field as the planet, and about 1' south and 14s. ± preceding. The position of this object would be, therefore, a=6h. 52m. 30s., 8=+17° 11'0; this position reduced to 1855 becomes a=6h. 5om. 21s., 8+17° 13'6, and there it agree with the position of any B.D. star. appears to be no such bright star in this place, neither does The actual elongation of Venus would exclude the possibility of the unknown object being an intra-Mercurial planet, although it does not preclude an improbable planetary body interior to Venus.

Although fourteen years have elapsed since the observation was made, Prof. Barnard has hitherto hesitated about publishing the results, but now thinks that they should

be placed on record, especially as his notes are very definite, and there could have been no known possibility of mistake.

Unless the unknown body was one of the brighter asteroids-and Ceres, Pallas, Juno, and Vesta were known to be elsewhere-the result is, as yet, entirely incomprehensible.

THE RIO DE JANEIRO OBSERVATORY.-We have just received the "Annuario " of the Rio de Janeiro Observatory for 1906, a useful volume which is published by the observatory, under the direction of the Minister of Industry and of Public Works, and which is the twenty-second of the series.

In addition to the usual calendars and tables of astronomical events, this volume contains numerous tables employed in astronomical reductions and conversions, tables for the reduction of meteorological observations, data employed in physical and chemical operations, and a résumé of the meteorological observations made in the Rio de Janeiro area during the year 1904.

IRON AND STEEL INSTITUTE.

IN place of the usual autumn meeting, the Iron and Steel Institute held a largely attended meeting in London on July 24 and following days jointly with the American Institute of Mining Engineers. At the opening meeting the president of the Iron and Steel Institute, Mr. R. A. Hadfield, gave an address of welcome to the American guests, expressing satisfaction that so many American engineers had been able to be present at this important international meeting. Sir James Kitson, who was president when the saciety first visited America in 1890, followed with a similar address of cordial welcome. Mr. Robert Hunt, president of the American society, in acknowledgment, said they felt as though they were part of the Iron and Steel Institute in that their society was formed on the same lines, and was equally camprehensive in its character and membership. The president announced that the King had consented to receive a deputation of the American guests, and also to honour the institute by accepting the Bessemer gold medal. He also announced that Sir Hugh Bell had been unanimously elected as his successor to the presidency in May next. Papers on Continental practice in blast-furnace gas engines were then read in abstract by the secretary, Mr. Bennett H. Brough. The first of these, by Prof. Hubert (Liége), dealt with the design of blast-furnace gas engines in Belgium. It reviewed the history of the direct utilisation of blast-furnace gas in engines since the early attempts in 1895, and gave particulars of detailed tests of a 1400 horsepower two-cylinder double-acting and tandem engine made by the Cockerill Company. Mr. Reinhardt's paper, on the application of large gas engines in the German iron and sfeel industries, formed an exhaustive treatise on the subject. The author showed that in the German ironworks there are 349 gas engines with a total effective horse-power of 385,000. He reviewed the practical experience gained by working, and with the aid of a large number of illustrations explained the present design of large gas engines in Germany. The old arrangement of the single-acting fourcycle motor, with one or more cylinders, has in recent years not been generally used, and, on the other hand, doubleacting four-cycle motors, mostly with tandem cylinders, are in keen competition with two-cycle motors. The author described in detail the cylinder and exhaust-valve chest, valve gear, shifting boxes, cooled pistons and piston rods, ignition and starting, and various engines of the doubleacting four-cycle type of the leading German makers, the remainder of the paper being devoted to two-cycle engines on the Oechelhäuser and the Körting systems. Suitable trials concerning the consumption of gas, Mr. Reinhardt remarked, are not available for comparison, and therefore it is not yet known how far the two-cycle engine is at the present time in this respect still inferior to the four-cycle engine. In conclusion, the author stated that the present position of the application of gas engines in German ironwarks shows the value the managers of these undertakings attribute to the better and less dangerous utilisation of the waste gases of their furnaces.

Mr. T. Westgarth (Middlesbrough) followed with a paper on large gas engines built in Great Britain. All the British builders were, he said, using the four-cycle system, except the builders of the Körting and Oechelhauser engines, who worked on the two-cycle system.

In discussion, Mr. Julian Kennedy pointed out that in the United States gas engines were only in their infancy. After further well-sustained discussion, the meeting adjourned. During the afternoon visits were paid to the National Physical Laboratory, to the London County Council's electricity generating station at Greenwich, to the Mercers' Hall, and to the Hall of the Armourers' and Brasiers' Company, and in the evening a reception was given by the Lord Mayor at the Mansion House.

On July 25 a crowded meeting was presided over by Mr. Robert W. Hunt (Chicago), president of the American Institute of Mining Engineers. His presidential address dealt chiefly with American rolling-mill practice, and concluded with the announcement that Mr. J. E. Stead, F.R.S., and Mr. R. A. Hadfield had been elected honorary members of the American society. The first paper read dealt with a comparison of American and foreign rail specifications, with a proposed standard specification to cover American rails rolled for export. The author, Mr. A. L. Colby, read the paper in abstract, and the proposal to admit o.1 per cent. of phosphorus was adversely criticised by Mr. Windsor Richards and other British members, the 0.07 per cent. recommended by the Engineering Standards Committee being considered safest for British practice. A paper by Mr. R. H. Lee, on producers in blast-furnace work, was briefly discussed, and the meeting adjourned. In the afternoon visits were paid to the works of Messrs. John I. Thornycroft at Chiswick, to the works of Messrs. J. and E. Hall at Dartford, to the halls of the Inner and Middle Temples, to Kensington Palace, the Imperial Institute, and the museums at South Kensington. In the evening there was a fête at the Imperial Royal Austrian Exhibition at Earl's Court.

On July 26 Mr. Hunt occupied the chair, but upon his proposal Mr. Hadfield presided. The first paper taken was by Mr. James P. Roe, on the development of the puddling process, and this was followed by a paper by Mr. James E. York on improvements in rolling iron and steel. These two papers, which are of extreme importance from a practical point of view, elicited an excellent discussion. The remaining papers on the British and American lists were taken as read. Many of these are of great interest and value, and we hope to publish abstracts of them in a subsequent issue. During the afternoon, visits were paid to the works of Messrs. Fraser and Chalmers at Erith, to the works of the Associated Portland Cement Manufacturers at Northfleet, to the Chelsea Power Station, and to the hall of the Ironmongers' Company. In the evening there was a banquet and special firework display at the Crystal Palace.

On July 27 the King received at Buckingham Palace deputation of the councils of the Iron and Steel Institute and of the American Institute of Mining Engineers, and accepted from the president, Mr. Hadfield, the Bessemer gold medal and a suitable illuminated address. The general body of members visited Windsor Castle, where special facilities were given them for seeing the palace and gardens In the evening there was a banquet at the Guildhall; Mr Hadfield presided, and the company numbered 600 included many distinguished guests. The American ladies, numbering 100, were entertained at dinner in two of the committee rooms, with Mrs. Hadfield and Lady LloydWise presiding.

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On July 28 there were alternative excursions to Messrs. Butlin's blast furnaces at Wellingborough and to the Dover harbour works. These two successful visits brought the Iron and Steel Institute meeting to a close. For the American guests visits were arranged, on Sunday, July 20, to St. Paul's Cathedral, the Roman Catholic Cathedral at Westminster, the Zoological Society's Gardens, the Botanic Society's Gardens, and to Hurlingham and Ranelagh Clubs, and on July 30 they started on a provincial tour, organised by the Iron and Steel Institute, to York, Ripan. Middlesbrough, Durham, Newcastle-on-Tyne, Glasgow, and Edinburgh.

SOME RECENT ASTRONOMICAL WORKS. THE appearance of another star catalogue from the Radcliffe Observatory shows how loyal that institution has remained to the traditions that Main and Stone received from Johnson and the earlier observers. The result is in every way worthy of those traditions. Other duties may have divided the attention of the director. The maintenance of the observatory in the first rank has demanded within the last few years that new and larger instruments should be erected, and the adjustment of these has necessarily taxed the energies of the small staff at the observers' disposal. But these imperative tasks have only had the effect of diminishing somewhat the number of stars observed. The accuracy and the independence of the observations, which have ever been a feature in the Radcliffe meridian measures, have in no whit suffered. In these respects the tradition of the observatory has been unflinchingly upheld.

The introduction to the volume shows that the stability of the instrument has been increased by structural alterations. The examination of the division errors, that tedious and laborious work, involving in this case more than ten thousand readings of the circle, has been manfully tackled with apparently greater care than Stone bestowed upon this fundamental work. The pivots have been tested by an apparatus that Dr. Rambaut himself has perfected. The results are apparently quite satisfactory. Finally, we are brought face to face with that troublesome R-D correction, the origin of which defies satisfactory explanation, as its treatment taxes ingenious applications. The method employed at Oxford is not the same as that which recommends itself to the authorities at Greenwich. At the former observatory no correction for this discordance has been made to the direct measures, the whole difference being applied as a correction to the reflexion observations in order to render the two series homogeneous. In the Greenwich observations of zenith distance, a correction is applied which has practically the effect of making the final result a mean between the direct and reflected observations. One may not say that it is a consequence of these different methods of reduction that the declinations obtained at Oxford and Greenwich show systematic differences. But when a comparison between the starplaces common to the two catalogues (Radcliffe, 1900, and Greenwich, 1890) is instituted, a systematic discordance is disclosed, the greater portion of which can be removed by reducing the Greenwich and Radcliffe observations in substantially the same manner. The zone catalogue of Albany also includes a large number of stars that have been observed at Oxford. A comparison between these two catalogues is most satisfactory. The difference between the two is practically the same as between Albany and Romberg's Pulkova catalogue. Of the accuracy of this latter Prof. Auwers has spoken in the highest terms. We may offer our congratulations to Dr. Rambaut on the successful completion of a heavy piece of work, and express the hope that the large equatorial, the mounting of which has interfered so much with the progress of his meridian measures, will amply fulfil its early promise.

The parcel from Groningen contains specimens of those laborious calculations to which the astronomers of that University are so much attached, and by which other astronomers have profited. Prof. Kapteyn here gives the results of his discussions of the proper motions of the greater part of the Bradley-Auwers stars on different assumptions of the value of the precessional constant, the position of the solar apex, and of systematic correc

"Catalogue of 1772 Stars chiefly comprised within the Zone 85-90 N.P.D. for the Epoch 1000, deduced from Observations made at the Radcliffe Observatory. Exford, during the years 1894-1003, under the direction of Prof Arthur A Rambaut, F.R.S. Pp. xxxvi+81. (Oxford: Henry Frowde, 100)

"Publications of the Astronomical Laboratory at Groningen." Edited by Prof. J. C. Kapteyn. Components of the Proper Motions and other quantities for the Stars of Bradley. Tables for Photographic Parallax-Observations by Dr W. de Sitter. Some useful trigonometrical formulæ and a table of goniometrical functions for the four quadrants, by Prof J C. Kapteyn and Prof. W. Kapteyn. (Groningen: Hoitsema Bros., 1906.)

Cours d'Astronomie," par Luis Maillard. Tome I. Pp. 243. (Paris: Librairie scientifique, A. Hermann, no date.) Price 7.50 francs "New Theories in Astronomy." By William Stirling. Pp. xv+336. (London: E. and F. N. Spon, Ltd., 1906) Price 8s. 6d. net.

tions to the proper motions in declination. Of the 3222 stars contained in Auwers-Bradley, 2640 have been discussed. Satisfactory reasons are given for omitting the remainder, so that the material may be considered exhausted. The results, grouped according to the galactic latitude of the stars or the type of spectrum, have been made the groundwork of special investigations. Since these have been before the astronomical world some time, it is not necessary to enter into any lengthy description here. The tables indicate a great amount of care and industry, and will be useful to those who wish to make independent investigations based on the proper motions of the stars.

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Dr. Sitter's contribution contains new and useful matter. The tables here arranged show at a glance the times of the year most suitable for making stellar parallax observations, on the assumption that the method of photography will be adopted and that the plates will be taken near the meridian. Some tables are also given that will be of Profs. use in the subsequent reduction of the measures. J. C. and W. Kapteyn add a collection of differential formulæ connected with the solution of spherical triangles. The authors believe that such formulæ would be of more general use if the amount of the neglected terms known with certainty. To remove this difficulty, the formula here given are correct to the squares of the differences. Convenience rather than originality seems to have influenced the authors, both here and in other formulæ applicable to plane and spherical triangles in which certain of the elements are small. Another table for which we have not yet found any extended use is one giving the trigonometrical functions for each degree in the circle to two places of decimals. But the authors say that mathematically trained persons have found it so useful in relieving their mind from mental strain, that they contemplate publishing a similar table giving the natural trigonometrical functions to three places of decimals for every tenth of a degree throughout the entire circle.

Such tables might possibly be of service to the readers of the next work on our list, "Cours d'Astronomie," by M. Louis Maillard, though, as the author does not vouchsafe any word of preface, it is uncertain for what class of students his book is intended. The purpose of the book is the more difficult to comprehend since we have but one volume of the work from which to judge of its aim and extent. But the writer of a text-book on astronomy has to keep within lines which are very well recognised. Especially is this the case when dealing with spherical astronomy. The facts do not materially change or increase. The only choice the writer can exercise is to decide between a work of reference which shall be as encyclopædic as possible, or a text-book which shall present to the reader a manageable amount of matter from which he may acquire an adequate grasp of the facts and M. principles upon which the science is supported. Maillard apparently prefers the text-book, and proceeds on the usual unheroic lines. He begins with the derivation of the ordinary formula of spherical trigonometry, to which he adds a few pages giving some elementary notions on the theory of least squares. But these few pages serve no useful purpose, and might have been omitted with advantage. When it is added that the author has some chapters on problems connected with diurnal motion, and a description of the constellations, it will be understood that he is catering for a class that is not very far advanced in astronomical study. But the chapters on parallax and aberration are generally full enough for all who have not to make any practical application of the theory. Finally, the section on the earth and geodetic measurement is made quite interesting. The book ought to have a ready appreciation among students in high schools and colleges, and is an advance on some of those which have long done duty in this country, and still enjoy an honoured position. The book is apparently lithographed, but it is very handsomely finished, and the diagrams are new and well reproduced. Of a very different calibre and purpose is Mr. Stirling's work. M. Maillard has been developed in an atmosphere of extreme orthodoxy. He is not, and has no wish to be thought, original. His methods have received the sanction of many generations of teachers. For good or for evil,

these methods have become stereotyped. But the late Mr. Stirling, as an engineer, had to think for himself, and, moreover, his occupation removed him to places far from the busy crowd. He could scarcely have had the opportunity of examining and testing his opinions by comparison with those of others who have been differently trained, for he passed much of his life in furthering railway enterprise

in Chili and Peru. There he was free to follow the lines of thought that his uncurbed fancies suggested. His book is therefore marked with much freshness, but also with some errors. In many respects it is interesting, since it shows the confusion which an intelligent mind may create for itself when it disregards the trammels of authority and attacks problems for the study of which it is not fitted by previous training.

We get the first insight into this mutinous disregard for authority when we find our author describing, in his first chapter, the experiments which the late Sir George Airy carried out at the Harton Colliery. It cannot be denied but that these experiments are open to some objection, though possibly not entirely on the grounds on which the author insists. But there is a certain refreshing keenness in his criticism which one can read and enjoy. We next find our author hopelessly blundering over that terrible question of the moon's rotation, and we cannot help thinking that the late Mr. Stirling must have had in his nature a considerable spice of obstinacy. He was far too intelligent not to have recognised the true character of the problem and to have found its solution. It is to be regretted, perhaps, that he did not rely upon his own good sense, and that he consulted so many authorities. He has our sympathy to the extent that these authorities have not always expressed themselves with clearness, and in some cases not even with accuracy. But with perverted ingenuity he seems to have fastened upon any looseness of expression he could find, and has endeavoured to give it a construction that it will not legitimately bear. But when we find the centrifugal force due to the moon's rotation introduced as a cause to explain the transference of air and water from the visible hemisphere of the moon to the hemisphere that we do not see, we are disposed to give up our author as incorrigible. It is not at all surprising after this that he should turn his attention to the nebular hypothesis, that he should find its explanation inadequate, and to need some finishing touches which he is ready to supply. For this is a subject that attracts those most keenly who are least qualified to handle it intelligently. Unfettered by close reasoning and unfamiliar with the bearing of material facts and deductions, they lose themselves in apparently plausible intricacies, and hopelessly puzzle those who attempt to follow them.

W. E. 1'.

UNIVERSITY AND EDUCATIONAL
INTELLIGENCE.

CAMBRIDGE.-Dr. H. W. Marett Tims, of King's College, demonstrator of anatomy in the University, has been appointed professor of biology at the Royal Veterinary College, London.

At a meeting of the president and fellows of Queens', held on Wednesday, July 18, Prof. H. T. Bovey, F.R.S.. professor of engineering in the University of Montreal, was elected an honorary fellow. Mr. Bovey was formerly a fellow of the society.

The master and fellows of Christ's College have elected Mr. Francis Darwin, foreign secretary to the Royal Society, honorary fellow. Mr. Darwin for many years held the readership of botany in the University and a fellowship at Christ's. Dr. G. H. F. Nuttall, F.R.S., has been elected a fellow of the same college. Dr. Nuttall has held teaching posts at the Johns Hopkins University, Baltimore, and at the University of Berlin. He is at present reader in hygiene at Cambridge and chief editor of the Journal of Hygiene, which he largely helped to found.

DR. G. C. BOURNE has been appointed Linacre professor of comparative anatomy at Oxford, in succession to the late Prof. Weldon.

A CLASS in experimental psychology, including practical work and demonstrations, will be held by Prof. C. S. Myers on Saturdays in the psychological laboratory of King's College, London, beginning on October 6.

MR. V. H. BLACKMAN has been appointed lecturer in plant cytology in the department of botany of University College, London. In view of the new relationship between the college and the University of London, and in order to avoid confusion with the principal of the University of London, the title of the Principal of University College will be changed to that of Provost of University College.

MR. CLARENCE H. MACKAY and Mrs. John W. Mackay have given 20,000l. to the University of California, to endow the chair of electrical engineering. It will be known, says Science, as the John W. Mackay, jun., professorship, in memory of Mr. Mackay's brother, and will be filled by Prof. C. L. Cory, head of the department of mechanical and electrical engineering.

THE Board of Education has issued its instructions for the year August 1, 1906, to July 31, 1907, to technical schools, schools of art, and other day and evening schools and classes for further education. As is becoming common in the Board's publications, the volume begins with a prefatory memorandum, and in it great stress is laid upon the value to the student of science and technology of what is commonly called " general "education. Steps are detailed by which the Board proposes to encourage this side of the work of these schools and classes. It is pointed out that the lower classes of a good evening school afford to pupils, who have just left an elementary school, both a continuation of their general training and instruction in the application of that training to matters that come before them in their daily work. It is where, savs the memorandum, this double aspect of evening schools is best developed, and where the lower and higher classes are most fully knit together, that the best records of attendance and of real progress are to be found. A distinct advance is recorded, we are glad to find, in the preliminary education of students entering higher classes in day technical schools, and this is to be traced to more efficient evening continuation schools. These regulations also make provision for an inclusive grant to local education authorities, other than London, in place of the separate grants assessed by taking into consideration the number of hours of instruction received by registered students in approved subjects. An authority wishing to receive such an inclusive grant must submit to the Board particulars of the manner in which it is proposed to make provision for the educational needs of the area and for the coordination of the several types and grades of this instruction with the other forms of education available for the area. All such endeavours to prevent overlapping and duplication of educational facilities, and to bring about economy and efficiency, are welcome. It is to be hoped the new plan proposed by the Board will effect the object in view.

SOCIETIES AND ACADEMIES.
LONDON.

Royal Society, June 21.-" The Transition from the Liquid to the Solid State and the Foam-structure of Matter." By Prof. G. Quincke, For. Mem. R.S.

On June 19, 1905, the author laid before the Royal Society the results of his researches on ice-formation and glacier-grains (see NATURE, September 28, 1905, vol. Ixxii., P. 543). The further prosecution of these researches has hown that phenomena similar to those observed in the freezing of water occur in all bodies in nature, and are in agreement with the structure of metals as observed by the author and also by other investigators. Solid bodies, then, are never homogeneous, but always exhibit a foam

structure.

All liquids in nature resemble water in forming, as they cool, oily foam walls, which may be very thin and invisible. The shape and position of these foam walls become visible on freezing or thawing in the following ways:-(a) By fissures or fractures at the surface of the foam walls,

whenever the liquid contents of the foam cells contracted on solidification, or when the walls and the contents of the foam cells contracted differently as they cooled. (b) By the bounding surfaces of the doubly refracting crystals glacier-grains), which are differently orientated in neighbouring foam cells. (c) On illumination with sunlight or electric light, or on warming, when the doubly refracting

contents of the foam cells melt and are transformed into singly refracting liquid. (d) By lens-shaped masses, foam fakes or air bubbles, suspended in the foam walls. (e) By the furrows, or network of lines on the solidified surface formed by the intersection with that surface of the foam walls in the interior of the solidified mass. (f) By polishing or etching the natural or artificial surface, in cases when the walls and the contents of the foam cells differ in hardness or in the rapidity with which they are attacked by chemical reagents.

The surfaces of solidified drops of pure molten metals show a network of straight lines or arcs of circles (usually inclined to one another at 120° or 90°), or foam walls with embedded lens-shaped masses. This is so in the case of gold, silver, platinum, palladium, iridium, indium, copper, zinc, iron, nickel, cobalt, bismuth, sodium, potassium and mercury. Similar phenomena are to be observed on the surface of solidified drops of sulphur and selenium, or on the surface of carbon which has been distilled with the electric arc in a magnetic field, and deposited on the kathode.

The shapes of the bounding surfaces of molten metals, and the circular arcs in the network of lines on the surface of metals raised to red or white heat, show that these bounding surfaces must be regarded, not as they have hitherto been, viz, as crystalline faces, but as solidified nily foam walls, which, as in the glacier-grains of ice, enclose foam cells with contents differing from the walls. Just as the glacier-grains of ice run together and enlarge by the bursting of the foam walls, so also larger foam cells with fewer foam walls are formed in metals heated nearly to melting point.

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Pure molten metals after solidification exhibit artificial polished and etched surfaces a network of lines or foam cells (similar to the glacier-grains of ice), which are bounded by thin foam walls. These thin foam walls themselves contain still smaller foam cells, as is proved by the visible lens-shaped masses embedded in them, and the wave-like furrows on their surface, which are capable in reflected light of giving diffraction colours like motherof-pearl. This foam structure of pure metals when solidified after fusion has been demonstrated in the case of bismuth, cadmium, cobalt, copper, gold, iron, indium, iridium, lead, manganese, mercury, nickel, palladium, platinum, potassium, rhodium, sodium, tin, and zinc.

Molten metals solidify on cooling to a liquid jelly, and later to a solid jelly. The walls and contents of the foam cells of such a jelly still consist of viscous liquid, i.e. the jelly itself is still liquid-like ice-at temperatures lower than the melting points of the respective metals. The welding of two pieces of metal corresponds to the running together of the cell walls and cell contents of two lumps of jelly, or the regelation of ice.

All the other substances in nature behave like these metals. The soft, plastic condition, which all bodies assume for a larger or smaller interval of temperature on the transition from the solid to the liquid state, proves the presence of jelly, i.e. of oily, visible or invisible foam walls, over this interval of temperature.

The heterogeneous oily liquid, which as solidification occurs becomes visible in all substances in nature in the form of thin foam walls of different surface tension, must also appear as a thin liquid skin on the surface of solidifying drops. This explains the variations in the measurements of the surface tension of molten metals and salts, and of liquids in general.

liquids, and are sufficient to explain the observed foam structure of all solidified substances in nature.

June 28." On the Ultra-violet Spectrum of Ytterbium." By Sir William Crookes, F.R.S.

The rare earth, ytterbia, was discovered in 1878 by Marignac (Comptes rendus, vol. lxxxvii., p. 578). In 1880 Nilson (Ber., vol. xii., p. 554), in purifying Marignac's ytterbia, found that it contained another earth, which he named scandia. Cleve, and more recently his daughter Astrid Cleve, have worked much on ytterbia, and within the last few years M. Urbain has taken up the subject, and has succeeded in purifying ytterbia in larger quantities. During the author's own work on the fractionation of the rare earths he also has prepared and worked with ytterbia.

M. Urbain's ytterbia was prepared by the fractional crystallisation of the ethyl-sulphates of crude gadolinite earths (Comptes rendus, vol. cxxxii., p. 136). The subsequent separation is by the fusing nitrate method. This after twenty series of fusions gave in the least basic portions a mixture of ytterbia and thoria, which are easily separated by Wyrouboff and Verneuil's method.

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The examination for absorption bands in a strong solution is a fairly good test for an earth such as erbia and thulia giving absorption spectra, but it is not so delicate an examination of the spark spectrum photographed through a quartz train, for dominant lines, which most elements show in some part of their spectrum. instance, the dominant lines of yttrium are at wave-lengths 3600-9, 3710-4, 37745. 4177-7, and 4375-1. The dominant lines of erbium are at 3499-3, 3692-8, and 3906-5. They are, however, not strong, and fortunately the absorption bands of this element are striking and characteristic. The spark spectrum of thulium has only been slightly examined by the author, and he does not think it has any strong lines. Its absorption spectrum, as with erbium, is a very characteristic one. The spark spectrum of ytterbium has strong dominant lines at 3289.5 and 3694-4. Scandium has 3572-7, 3614-0, 3630-9, 3642-9, and

dominant lines at

4247.0.

The author's photographs were taken with the quartz apparatus already described, the spectrum of pure iron being used as a standard. The ytterbium spark was taken from a strong solution of the nitrate between platinum poles, sufficient self-induction being introduced to eliminate nearly all the air lines. The ytterbium, by this very severe spectrum test, is seen to be not absolutely free from impurities-thulium, copper, and calcium being present. Thulium is seen by its lines at 3020-7, 3131.4. 3425.2, 3441-6, 3462.4, and 3848.2. Copper is seen by its dominant lines at 3247.7 and 3274-1, and calcium by its dominant lines at 3933-8 and 3968.6.

The platinum lines which are present are easily recognised, and are useful as an additional measure of identification. Besides these, a number of fainter and indistinct lines are seen. These may be due to ytterbium or to traces of hitherto unrecognised impurities.

The wave-lengths of all the recognisable lines of ytterbium are given on the photograph, and also those of thulium, calcium, and copper, but the platinum lines are not marked.

:

PARIS.

Academy of Sciences, July 16.-M. H. Poincaré in th chair. The absorption of nitrogen by organic substances, determined at a distance under the influence of radio-active materials M. Berthelot. The action of air upon cellulose in the presence of a radium salt has been studied; the effects are comparable with those produced by the silent discharge.-A photometer specially designed for measuring the circumsolar light. Its use during the total eclipse of August 30, 1905: H. Deslandres and A. Bernard. The standard light used in the comparisons was a small osmium lamp. Two diagrams are given show

The walls and contents of the foam cells consist of heterogeneous substance. That foreign matter in very small quantities-1/1000000 per cent. and even less-does forming the arrangement of the photometer and telescope.

oily layers and foam walls in pure liquids is proved by the author's observations on ice and benzene. Traces of foreign matter (gases, carbon, metals, &c.) too small to be shown in any other way are present even in the purest

The apparatus was used at Burgos during the last total eclipse, but the meteorological conditions were unfavourable.-Study of an apparatus designed by M. Lippmann for the photographic measurement of right ascensions: W.

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