Observers were stationed at various distances up to 54 kilometres from the signals, and naked-eye records were taken. There were three sets of experiments, to determine (1) the relative advantages of circular and flat-wick lamps; (2) the range of red and green lights; and (3) the distance at which two separate lights can be distinguished. The results showed (1) that the light from the flat wicks was considerably brighter at a distance than that from the round wicks, particularly when the line of vision formed a right angle with the sides of the wick, and (2) that the range of the red lights (flat wicks) was approximately double that of the green, the latter being scarcely visible at 3 kilometres, while the former were still bright at 5 kilometres. In the third set of experiments observations were taken at distances of 2 and 3 kilometres of pairs of lights separated by intervals of 2, 3, 4, and 5 metres. At 3 kilometres none of the pairs were distinguishable as separate lights when the space between them was less than 4 metres. With a separation of 2 metres red or green pairs were merged into one bright light. When red and green lights were shown simultaneously, the green light was eclipsed altogether by the red at 2 kilometres if the distance separating them was not more than 2 metres. PART 15 of the Verhandlungen of the German Physical Society contains a description of a mechanical pump for high vacua recently devised by Dr. W. Gaede, which makes use of a principle not previously utilised in the construction of such apparatus. If a shaft revolving in a well-fitting bearing has a circular slot cut in it, the air in the slot will to a large extent be carried round with the shaft. If at one part the bearing projects into the slot so as to fill it completely, the gas in the slot will be carried round with the shaft from one side of the projection to the other, and the pressure will in consequence be less on one side than on the other. If two openings are made through the bearing, one on each side of the projection, air will be drawn in through one and delivered through the other. By making a number of slots in the shaft and connecting the openings into them in series, the action will be intensified. A pump constructed on these lines exhausts five or ten times as fast as one of Dr. Gaede's well-known mercury pumps taking the same power, and deals with the water vapour as well as the gas, so that no drying materials are necessary. As it works better at low than at high pressures it is run in conjunction with another pump, which reduces the pressure to a few centimetres of mercury. IN a publication of the R. Accad. delle Sci. dell' Inst. di Bologna, which has recently come to hand, Prof. A. Righi describes some interesting experiments on the emission of ions in directions perpendicular to that in which the main discharge passes. Two wire electrodes are sealed into a cylindrical vacuum tube, perpendicular to the axis, with only their points exposed. When an impulsive discharge is passed between them it is found that ions are shot along the axis of the tube. The distance they penetrate and their relative numbers under different conditions are studied by collecting them in a suitably placed Fara day cylinder. By an ingenious arrangement of vanes, which rotate when the ions strike them, it is possible to follow the paths of the particles. This transverse emission of ions is most vigorous near the ends of the main discharge. When the tube is placed in a magnetic field parallel with its axis the neutral doublets, already investigated by Prof. Righi in earlier papers, are formed, and, as would be expected, the Faraday cylinder collects less charge. On the other hand, owing to the large mass of the doublets, the mechanical effects are increased. AN article in Engineering for October II recalls the discussion of a few years ago on the distribution of shearing stresses on the horizontal layers of a dam. Messrs. Wilson and Gore showed experimentally in 1908 that the stresses did not follow a parabolic distribution, but were much more uniform. Prof. E. G. Coker has lately described experiments at the Royal Society on thin celluloid sheets under shearing stress, the conditions resembling that of the web plate of a plate girder. It has been contended that the shearing stresses in the girder web follow the parabolic law, but these experiments indicate that this law is only approached when the plate is shallow. Otherwise the shear curve had no maximum at the centre of the specimen, but showed two equal maxima, which are at points situated at a distance from the ends equal to rather less than the width of plate under test. Reducing the depth of the plate causes these two maxima to approach each other, and they finally coalesce when the depth of the specimen is about equal to its width. A SECOND edition of Mr. T. H. Byrom's "Physics and Chemistry of Mining: an Elementary Class-book for the Use of Mining Students," has been published by Messrs. Crosby Lockwood and Son. In this edition the chapter on magnetism and electricity has been omitted, and additional matter has been introduced in both the physical and chemical sections. The price of the volume is 3s. 6d. net. MESSRS. H. F. ANGUS AND Co., of Wigmore Street, London, have issued a new catalogue of second-hand scientific apparatus and accessories which are available for sale, exchange, or hire. We notice that all the instruments listed, unless otherwise stated, have been tested, adjusted where necessary, and are capable of work of equal precision as when new. Interesting particulars are given in the list of microscopes and accessories, as well as of various other optical instru ments. OUR ASTRONOMICAL COLUMN. GALE'S COMET, 1912a.-London urban skies have remained comet-proof for some time now, but Mr. Franks, writing to The Times (October 15), reports that he saw Gale's comet very well, with a 6-inch refractor, during the week ending October 11, at East Grinstead. He states that it appeared to be brightening, for it was about fifth magnitude when he first saw it, and was nearer fourth on October 11. On this date it was a fine object, plainly seen in the finder, and, by sighting along the telescope, it could be seen by the naked eye as a misty spot about half a degree below a Serpentis. When seen on a dark sky it presented an extensive coma with a large bright nucleus and a tail at least half a degree in length. Mr. Franks also reports that it was nearly a degree north of its predicted position on October 11, and that the difference is increasing, but it seems probable that he was using the earlier ephemeris published by Dr. Ebell, and not the later one from which we gave an extract last week. The following is a continuation of the corrected ephemeris : 8 (true) 1912 a (true) b. m. Oct. 18...15 49'9...+13 20'0 19...15 510...+14 14'6 20...15 521...+15 8.2 21...15 531...+16 06 1912 a (true) h. m. 8 (true) Oct. 22...15 541...+16 520 23...15 55°...+17 42'5 24...15 561...+18 320 25...15 570...+19 20'5 According to this ephemeris, the magnitude should now be 6'6, and decreasing slowly, but, as Mr. Franks remarks, the comet is exceeding expectations, and, with its indications of abnormal brightening, may well repay careful observation, especially in the form of a close series of photographs, by those who are favourably situated; on October 21 the comet will be about one-third of a degree east of y Serpentis. THE RECENT TOTAL ECLIPSE OF THE SUN.-It is with much regret that we learn from Greenwich that all attempts to make observations of the recent total eclipse of the sun were frustrated by the heavy rain which prevailed in the eclipse region of Brazil on eclipse day, October 10. The Greenwich observers, Messrs. Eddington and Davidson, were located at Alfenas, an elevated village some 185 miles north of Santos, where there were also eclipse parties from France, Germany, Brazil, and other countries. The Brazilian officials rendered all the assistance they could, and the Government voted a sum of 5000l. for the reception of the visiting astronomers at Rio. According to characteristically interesting letter from Mr. J. J. Atkinson, which appeared in The Morning Post on October 8, the Greenwich equipment weighed about three tons, and had to be transported from Rio to the terminus of the State railway, a distance of about 150 miles towards the mountains; owing to the sharp incline the latter part of the track has to be worked on the cog system. Mr. Atkinson, who accompanied the Greenwich observers as a volunteer, also recites some interesting reminiscences of his previous eclipse experiences. a THE CONSTANT OF ABERRATION.-In No. 15, vol. xxvii., of The Astronomical Journal, Prof. C. L. Doolittle gives the result of twenty-two determinations of the aberration constant derived from thirty-two years' latitude work at the Sayre and Flower Observatories. The observations were made at two different places, with what are practically four different instruments, only the observer remaining the same, and the mean probable error is less than o'or". Taking the weighted mean of all the observations, Prof. Doolittle finds for the constant the value 20 ̊525" ±0.0043", and the corresponding value for the solar parallax is 8'780". THE AUTUMN MEETING OF THE THE papers presented at the autumn meeting of the Institute of Metals, which took place at the Institution of Electrical Engineers on September 25 and 26, may be divided into two groups according as their interest lies principally on the practical or on the scientific side. Among the "practical" group two papers dealing with the joining of non-ferrous metals and alloys may be mentioned. In these Prof. Carnevali, of Turin, and A. E. Tucker, of Birmingham, discuss the question of autogenous welding, although the latter paper also deals in an interesting if somewhat scrappy manner with many other processes, such as soldering and brazing, &c. In view of the great extension of autogenous welding by means of oxygen and acetylene, the question how far the results of this process can be trusted is an important one. Tucker appears to regard a weld as satisfactory if it is found on testing it to destruction that the fracture occurs away from the weld itself. As a matter of fact, however, the weakest portion of a welded joint, as Carnevali points out, is not the weld itself, but the region of injured metal on either side of it. According to this author the strength of welds in copper and its principal alloys cannot be depended upon, and this conclusion agrees with the views on autogenous welds in iron and steel recently expressed by Fremont and others. In regard to pure aluminium, however, Carnevali finds the method to give satisfactory results, but the efficiency of a weld is much reduced as soon as it is applied to one of the stronger light alloys of aluminium. Broadly speaking, these papers lead one to view the rapid development of autogenous welding practice with some suspicion. Still on the "practical" side were a number of papers dealing with impurities in copper and copper alloys. An interesting and suggestive paper by E. F. Law dealt with oxygen and oxides as deleterious impurities in alloys. This author took the view that progress in non-ferrous alloys was largely a question of the better elimination of oxides, and this view was strongly supported in the discussion by Rosenhain. The paper by Prof. Turner, however, emphasised the existing difficulties in the way of analytical determination of oxygen in brass, and an appeal was made to chemists to devise a satisfactory method for this purpose. F. Johnson dealt with the effect of impurities, chiefly antimony, on the properties of tough-pitch copper, and here again discussion centred round the part played by oxygen. The lenient view as to the deleterious effects of antimony put forward by the author was, however, strongly opposed by all those who have to deal with copper on the large scale. Other papers of a "practical" character dealt with high-temperature tensile tests on copper and its alloys, and with the annealing of coinage alloys, and both these papers were vigorously criticised in the discussion on the ground of the experimental methods employed by the authors. The "scientific" papers were not so numerous, but of special interest. Prof. H. C. H. Carpenter contributed two papers dealing in further minute detail with the inversion which he has discovered in a certain range of copper-zinc alloys (brass) at a temperature of 470° C. In one of these papers the author deals with the effect of impurities on this inversion and finds that any addition of a third metal to these alloys tends to facilitate rather than to inhibit the transformation in question; since the change renders the metal weak and more brittle, it is evident that the use of the purest copper and zinc is desirable in the manufacture of those varieties of brass containing the constituent. In a very short note Dr. G. T. Beilby, F.R.S., discusses the phenomena of the solidification of metals from the liquid state in reference to the "foam cell " theory of Quincke. In his May lecture to the institute, Dr. Bielby had suggested the importance of a full experimental investigation of the views put forward by Quincke, and the present note is intended to state more precisely the problem which Dr. Beilby desires to see investigated. The fundamental question, which goes beyond Quincke's hypothesis, is this, whether the liquid metal undergoes any changes or separations before actual solidification commences, and, if so, whether there is really any formation of foam cells or analogous structures governing the crystallisation of the metal. In his note Dr. Beilby quotes some lines of evidence from the manner in which a thin film of fused salt or other substance solidifies on a glass slip which appears to be strikingly contradictory to Quincke's views, and indeed the impression derived from reading Dr. Beilby's note is rather that he finds the "foam cell" theory less attractive after thus considering it more closely. A practical result is, however, likely to follow from Dr. Beilby's interest in the matter, in the shape of an exhaustive report on our present knowledge of the passage from the liquid to the solid state in metals, prepared under the auspices of a committee of the Institute of Metals, and this will certainly be very welcome. Of purely theoretical interest is the paper presented by Dr. Rosenhain and Mr. Ewen, of the National Physical Laboratory, on the intercrystalline cohesion of metals. In this paper the authors advance the hypothesis that the crystals of a pure metal are held together by the action of a thin layer of metal in the amorphous condition forming a species of cement between the crystals. The conception of the existence of such a cement has already been put forward by Bengough and by Osmond, but the authors claim to have used it as a working hypothesis in their own laboratory before others had published their views. The paper begins with a detailed discussion of the general facts which lead in the first place to the idea that there should be some special condition at the boundary surfaces of crystals in solid metals; perhaps the most striking of these facts is the strength of these bounding surfaces, since it has been conclusively shown that pure metals normally undergo fracture through the crystals and not along the boundaries between them; the cohesion across these bounding surfaces is thus stronger than that across the cleavage planes of the crystals themselves. The authors next suggest in general terms that when two growing crystals approach one another, a region is formed at their boundary in which the molecules are no longer able to assume the crystalline arrangement, and they further point out that if the unit or element of which the crystal is built up is large compared with the "liquid" molecule, then at the junction of two crystals gaps must remain which are too small to contain another complete crystal unit and that consequently such gaps would ultimately be filled by undercooled liquid metal which had been unable to crystallise. This undercooled liquid would then be identical with the "amorphous phase" of Beilby, and would possess similar properties. The paper points out that Beilby has shown that the amorphous phase is more soluble in acids and possesses greater chemical activity than the crystalline phase, and it would accordingly possess a higher vapour pressure under corresponding conditions of temperature. It follows that if two pieces of the same metal, one containing a small and the other a relatively large proportion of amorphous matter, were heated to the same high temperature in a high vacuum, the one containing the larger proportion of amorphous matter would lose weight more rapidly than the other. This conclusion the authors have submitted to the test of experiment in the following manner. If an amorphous intercrystalline cement exists, then specimen of metal consisting of a few large crystals a OCTOBER 17, 1912] NATURE intercrystalline boundaries is clearly visible on the Incidentally, the method of heating metals in high vacua furnishes an interesting means of developing their micro-structure, and this method has been used by the authors to study the conditions under which One of their twinned crystals are developed in silver. photomicrographs showing the structure of a twinned crystal of silver is reproduced in Fig. 2. THE SURFACE-TENSION OF LIVING PROF. CELLS.1 CZAPEK'S pamphlet contains most important experimental work upon one of the fundamental physical attributes of the living protoplasmic cell, namely, the surface-tension of its external limiting layer. He makes it clear that the tension conditions obtaining in this layer, which intermediates between each metabolic unit and its environment, are of great significance for secretion and for absorption, and he has established that the surface-tension of the cells of the higher plants is maintained fairly constant at the value of about 0.685, the surface-tension of water in contact with air being taken as unity. 46 " This very important conclusion is the outcome of a line of research which began at an apparently remote point, the successive stages of which may be briefly set out. The work started with the investigation of the curious precipitates that could be produced in the living cells of many plants by the action of dilute ammonia or 0-2 per cent. caffein, such as had been described as aggregation" by Charles Czapek first Darwin, in the tentacles of Drosera. precipitate is a established that this "myelin-like compound of caffein with the soluble tannin of the living cell, and is produced in all cells that contain tannin, the mesophyll of Echeveria and Sedum being the most suitable material. He then found that if such living cells are immersed in solutions of organic substances for some hours, the power of giving a precipitate with caffein may be entirely lost. This loss was traced to exosmosis of the tannin from the living cell, and it was further found that for each a particular limiting organic substance there was concentration below which no effect was produced and above which the exosmosis became very rapid. On comparing these limiting concentrations for the series of monovalent alcohols it was found that at each step in the homologous series the molecular concentration required diminished to one-third. relation was, however, exactly what Traube had established for the surface-tension effect of the members of this series. Such a 1" Ueber eine Methode zur direkten Bestimmung der Oberflächenspannung By F. Czapek. Pp. iv+86. (Jena: der Plasmahaut von Pflanzenzellen." Gustav Fischer, 1911). Price 2.60 marks. Following up this clue, Czapek measured the surface-tension of a large number of solutions of organic substances, and compared their action in causing exosmosis from the cell with their activity in lowering the surface-tension of water. He thus was able to establish securely the unexpected generalisation that on dissolving in water sufficient of any organic substance whatever to lower the surfacetension to about 0.685, a solution is obtained which just causes the exosmosis of the contents of living cells. The critical concentration may require twelve to twenty-four hours to produce its effect, but stronger solutions with a lower surface-tension work very quickly and thoroughly, so that after a short time treatment of the cells with caffein gives no intravital precipitate at all. The power of the protoplast to retain its dissolved contents is thus shown to be a matter of physical organisation, depending upon the surface-tension of the cell being below that of the medium in contact with its outer surface. From true solutions Czapek passed to try the effect of emulsion-colloids of a lipoid nature (proteids and carbohydrates do not lower surface-tension enough to give the critical value of 0-685). The lipoid emulsions are, however, extremely active, and give exactly the same effects as true solutions. The last step in the progress was an attempt at identification of the substance actually present in the plasmatic membrane which causes it to have normally so low a surface-tension as 0.685. Czapek finds that saturated emulsions of neutral fats lower the surfacetension just to this value and no further, so that it seems very probable that these are the effective substances in the living cell. We have thus striking support for the view, widely adopted from the work of Overton and Meyer, that a lipoid nature. the plasmatic membrane is of Overton's later view was that lecithin and cholesterin rather than neutral fats were the particular lipoids present, but these give a lower surface-tension down to about 0.5. The present line of work indicates that these may be the effective substances in some cells, not those of the higher plants, for yeast and red-blood corpuscles require a medium of about this exosmosis of lower surface-tension to bring on invertase and hæmoglobin respectively. Many supporters of the lipoid theory of the constitution of the plasmatic membrane have interpreted it to mean that there exists at the surface of the cell a continuous film of a lipoid nature, and this has raised difficulties in understanding the intake of typical nutrient substances which are freely soluble in water, but not in fat. Czapek points out that an emulsion containing only a small percentage of fat is all that is needed to endow the cell with the observed specific properties. Willard Gibbs showed from thermodynamical conwhich siderations that substances in a solution strongly reduce surface-tension must accumulate in the surface-layer until their return by local excess of osmotic pressure produces a state of equilibrium With emulsified between the surface and the mass. the osmotic pressure is fat particles, however, very slight, and very great accumulation in the surface-layer must result. This piece of work may serve as a model of scientific method on account of the way in which the mysterious phenomenon of "aggregation," described by Charles Darwin, has been followed on and on until it has led to the evaluation of so fundamental a vital constant as the surface-tension of the living F. F. BLACKMAN. cell. THE BRITISH ASSOCIATION AT DUNDEE. SECTION L. EDUCATIONAL SCIENCE. OPENING ADDRESS BY PROF. JOHN ADAMS, M.A., B.Sc., LL.D., PRESIDENT OF THE SECTION. An Objective Standard in Education. Of those who deny to education a place among the sciences the name is legion, for they are many. The mere classification as a science is not perhaps of much consequence, but it is useful for the student of education to examine the popular view, and see how far it is justified. The following statement, the words of a former occupant of this chair, will be generally accepted as representing the prevailing opinion: "If we take science to mean, as commonly understood, organised knowledge, and if we are to test the claim of any body of facts and principles to be regarded as science by the ability to predict, which the knowledge of these facts and principles confers, can we say that there exists an organised and orderly arrangement of educational truth, or that we can logically, by any causative sequence, connect training and character either in the individual or in the nation? . . . It is very doubtful whether we can say that educational science is yet sufficiently advanced to satisfy these tests." First, with regard to organised knowledge, there is certainly a great mass of matter available in the subject of education. It is true that there is nothing easier than to show that this matter is not at present well organised. It is only too easy to find examples of contradictions among those who make a study of education and venture to write or speak on the subject. We are told that there is scarcely any important statement made by a writer on education that cannot be met by a direct contradiction in the works of some other educational writer. It has to be admitted that writers on education in the past have been strangely opinionative and dogmatic in view of the very complex and delicate problems they have had to handle. Too frequently they assumed a simplicity in their subject-matter that was certainly not there. Even the massive common sense of Dr. Johnson was not able to keep him from regarding education as a study that had reached its limits long before his time. But between those who regard education as too simple to need any further examination, and those who treat it as so complex as to defy human analysis, there are those who take the view that education is a science like any other, though they admit that there may be room for wide difference of opinion regarding the stage of development it has reached. At the present moment it is becoming increasingly evident that educational theory is consolidating: it can now be claimed that there exists a great body of educational doctrine that is of general acceptation. It need scarcely be said that there are many and deep differences among the various schools of educational writers. But if we compare any two schools we shall find that the points of agreement far outnumber the points of difference. This was true even in the older times of naïve theory, but is making itself very evident in these latter days. Anyone who occasion to read all the books on the theory of education as they appear is impressed in spite of himself by the large body of doctrine that is common to them all. It is not that the books lack originality: each writer has his new point of view or his new interpretation of certain phenomena; yet each either baldly states or tacitly takes for granted a great body has of truth that is held to be generally accepted. This body of recognised truth is gradually increasing as the result of collective thinking and the corrections involved in active criticism. Already critics are beginning to find fault with any writer who produces a book-not avowedly a text-book-that professes to deal with the whole range of education. He is reminded that what is now wanted is a special development along certain definite lines. The general principles of education are held to be established and accepted. In confirmation of what has been said, it may be added that within the past year or two have appeared no fewer than five separate treatises each bearing the same title: "The Principles of Education." These books are mainly for the use of students, and contain what are regarded as the accepted results of educational investigation up to the present date. Their authors obviously recognise the existence of a certain body of truths on which all are agreed. In some of the professions it is customary to speak familiarly of "the books," meaning the standard works to which appeal is constantly being made. If among teachers we have not yet reached this stage, we are obviously far on the way towards it. The books are there, but the profession needs some time yet before, in its own deliberate way, it recognises their importance. By and by it will realise the fact that it has at its disposal material that will enable it to prophesy, and thus fulfil, the second condition imposed upon all who lay claim to scientific knowledge. It is true that in the past there was little diffidence about prophesying it was the fulfilment that gave trouble. Wolfgang Ratke supplies, if not the first, at any rate the most dramatic application of a control test in the He working of educational prophecy. went to prison because the people of his time did not make allowance for the insufficiency of the body of knowledge on which he based his predictions. There was indeed nothing scientific about the procedure of Ratke. He was at the empirical stage, and could not rise above it. His modern fellows have not quite got beyond the empirical, but they are on their way. No claim is here made that Education has yet justified her demand to be recognised as a fully developed science; but it may be fairly maintained that she has at least entered upon the stage of scientific method she is seeking to free herself from mere empiricism. In such a struggle there are at least two possible lines of action. The first requires some ingenuity, but is natural and pleasant. It consists in superimposing principles upon the facts of the case. The educational theorist invents or assumes certain broad general principles. then proceeds to fit in all the observed facts, and often shows great skill in the process. This method is of very general application. Sometimes it is worked consciously and deliberately, as in the case of Socrates' doctrine of Reminiscence. Here we have the whole scheme of teaching simplified by this superimposed generalisation. Quite frequently, however, the broad underlying principles are not brought to clear consciousness, and are, in fact, sometimes contradictory to each other. Examples may be found in Rousseau. For our present purpose this tendency towards what may be called rational pedagogy is best illustrated in the system of education elaborated by Herbart. Though the metaphysical basis on which he builds is generally regarded as false, it was deliberately adopted by him, and if it is once granted to him, all the rest of his system must be admitted to be built up on strictly scientific principles. It is true that while logically Herbart's pedagogy was built upon his psychology, in point of fact his peda |