unable to fly at all except on a windy day, when, by facing the wind, it would be able to rise to a considerable altitude before its inertia was overcome.

IN connection with the foregoing paragraph we may take the opportunity of referring to the marked discrepancy in the matter of nomenclature which distinguishes the papers of systematic specialists from those of biologists with a wider range of studies. In Prof. Lull's paper, for instance, the flying-lemur is referred to by the timehonoured title of Galæopithecus, whereas in a recent paper by Mr. G. S. Miller (Proc. U.S. Nat. Mus., No. 1481) we find it figuring as Cynocephalus, a name until recently used for the baboons. As the president of the Bavarian Ornithological Society remarked in his address for 1904, in connection with the proposed transposition of the names Tardus musicus and T. iliacus, "all these changes of longestablished names, even when the alteration was justifiable, should be most rigorously guarded against, as the greatest confusion would be the only result."

IN addition to Prof. Lull's communication, the August number of the American Naturalist contains an article by Messrs. Dexler and Freund on the external morphology of the dugong, which is illustrated with reproductions from photographs throwing new light on the form of the muzzle. In the third article Mr. M. L. Hammatt describes the manner in which the anemone Metridium marginatum multiplies by fission. After either natural or artificial fission, "the fragment cut off curls together until its extremities meet, making parts of mesenteries before nearly parallel now radial in position, thus attaining to the seaanemone structure with the least possible expenditure of energy."

IN vol. xxii., art. 2, of the Bulletin of the American Museum of Natural History, Prof. H. F. Osborn publishes a complete description and restoration of the skeleton of the gigantic carnivorous dinosaur Tyrannosaurus from the Upper Cretaceous of North America. The creature stood about 16 feet, to the crown of the head, and there is a possibility that it may have carried an armour. The most remarkable feature in its osteology is the presence of a series of abdominal ribs comparable to those of the tuatera (Sphenodon), such structures having hitherto been unknown either among dinosaurs or crocodiles. The author states, however, that they have been found to exist in the allied genus Allosaurus, and suggests that they may also be represented in the herbivorous sauropodous dinosaurs, in which group they have been regarded as referable to the shoulder-girdle.

As a contribution to the Hann jubilee volume of the Meteorologische Zeitschrift, 1906, Dr. J. M. Pernter has selected the interesting subject of the determination of the size of cloud components from the phenomena of optical meteorology, e.g. halos and coronæ round sun and moon, and glories such as formed by the shadow of the observer, like the Spectre of the Brocken, &c. Among the first to undertake the measurements of the ice-crystals or minute rain-drops were Fraunhofer and Kämtz. Many of these measurements have been re-calculated, together with much additional information obtained chiefly from observations made on Ben Nevis, by using the revised formulæ of Airy and Verdet. These measurements are given in detail in several tables; the general conclusions arrived at are that both in clouds and fogs, up to the altitude of the highest clouds, the diameters of the ice-crystals are from about 5 μ to 20 μ, and that consequently 5 μ is the lower limit of the

thickness of the ice-prisms. For rain-drops in clouds and fogs the diameters are found to be between 20 μ and about 100 μ. Dr. Pernter points out that these dimensions only hold good when no precipitation is falling, and further that it does not follow that still smaller ice-crystals, &c., may not be floating about in the clear atmosphere, their number being too few to cause any visible appearance of condensation.

In a memorandum (dated August 5) on the meteorological conditions in Egypt and the Sudan during July, Captain Lyons, director-general of the Survey Department, estimates that the Nile flood will be near the average this year, so far as information is at present available; the critical period is said to be the first ten days of August, as the volume of the flood depends on the level attained by the Blue Nile being maintained for a sufficient time during this month. The rainfall recorded at the principal stations around the Nile basin in July shows that the excess, which had been persistent since the beginning of the year, is now, however, replaced by a deficiency, while the fall over the Sudan plains has been somewhat above the average at most stations from which observations have been received.

THE Psychological Bulletin (vol. iii., No. 4) contains an article by Prof. G. M. Stratton on the character of consciousness. The conclusion to which the writer comes is that consciousness is either the generical mark of all psychic processes or else a special one of these processes, viz. that of knowing. If, therefore, we apply the term consciousness to the act of cognition, it should not be understood that knowing is the supreme function in the world of objects, or that it really breaks loose from those connections with feeling and will which modern psychology has recognised." Consequently, it seems to him that it would be best to say "knowledge" when we mean "knowledge," and to let the term 13 consciousness designate the common and generic features of our psychic acts.

THE Bulletin de l'Institut Général Psychologique (5o Année, No. 6) contains two interesting articles, one a full account of the marine laboratory at Wimereux, founded in 1874 by Prof. Giard, the other on the fifth international psychological congress held at Rome last year. A short account is given in this last of the dispute between Flechsig and Sciamanna regarding the localisation of functions in the frontal and pre-frontal regions. The former maintained that all the frontal region corresponded to the most elevated associations, the feelings of personality, of self-consciousness, and of self-control, and that to the pre-frontal region in particular belonged voluntary action. Sciamanna, alter experiments on monkeys, came to the conclusion that in them, at any rate, the pre-frontal lobes could not be considered as the seat of intelligence, morality and the like, but that these higher functions ought to be considered, as a rule, the result of the regular and harmonious working of the cerebral mass as a whole, and that any disturbances consequent on lesion were to be attributed to the rupture of this complete harmony. A committee appointed to examine the monkeys before and after death confirmed Sciamanna's account of their undisturbed mental condition. but, on the other hand, found that the removal of the frontal lobes had not been so complete as Sciamanna believed.

THE Manchester Microscopical Society has just issued a revised list of the lectures arranged for delivery by members of the extension section of the society during the coming winter. The object in view by the section is to

bring scientific knowledge, in a popular form, before societies unable to pay large fees for professional lectures, and all fees paid for lectures are devoted to the working expenses of the section. Applications for the list by the secretaries of natural history and kindred societies should be made to the honorary secretary of the extension section of the Manchester Microscopical Society at 22 Filey Road, Fallowfield, Manchester.

MESSES. WRATTEN AND WAINWRIGHT have sent us a batch of their panchromatic plates, which have been recently prepared in response to the demand for a plate having more uniform sensitiveness to the various spectral colours. Very searching tests on photographs of various spectral radiations show conclusively the unique qualities of the new emulsion. For instance, on a photograph of the spectrum of the iron are the green region, usually difficult to obtain with such exposures as give the blue of normal density, is shown of actually greater density than the blue; at the same time, the red end of the spectrum is very uniformly rendered up to A 7600, and with slightly longer exposure somewhat beyond this. This particular batch of plates was of medium rapidity, the sensitiveness measured to daylight being 94 H and D, 138 Watkins and F/94 Wynne. Development took about 3 minutes for most of the exposures tried, and the plates were clear and clean in working. An important factor in spectroscopic work is the fineness of the grain of the silver deposit, and in this respect the Wratten panchromatic is excellent. There is no doubt that for spectrum investigation extending over the whole region from ultraviolet to extreme red these plates are the most satisfactory at present obtainable. If one might be permitted to ask for further convenience, it would be to maintain the present colour sensitiveness ratios, and endeavour to in

crease the general rapidity. Should it be found possible to do this and, at the same time, keep the grain within reasonable bounds, this type of emulsion would be of immense service for stellar spectrum photography, as for this purpose a rapid plate is essential on account of the feebleness of the light. A notable feature of the instructions sent out with the plates is the provision (for the first time, so far as we are aware) of a table showing the normal time of development for varying temperatures. It is well known that the temperature of the developing solution has a considerable effect on the speed of appearance and subsequent growth of the latent image, and as the new plates are practically equally sensitive to all colours, requiring development in darkness, it is very advantageous to be able to control by time the correct duration of the process. The figures given for this purpose are not arbitrary, but have been obtained from exhaustive experimental trials, and can therefore be relied on without hesitation to give comparatively uniform results. The developer recommended is a very weak combination of metol hydroquinone, but excellent results have been obtained with other ordinary developers, some much more concentrated, so that no difficulty is likely to be found from this cause when the time best suited to the developer chosen is once determined.

Two more parts of Prof. O. D. Chwolson's "Traité de Physique," which M. A. Davaux is translating into French from the Russian and German editions, have been published in Paris by M. A. Hermann. The first parts of vols. i. and ii. were reviewed at length in our issue for February 15 last (vol. xxiii., p. 362), and the present fascicles are the second parts of these volumes. The former deals with the gaseous state of bodies, and the latter with indices of refraction and the dispersion and transformations

of radiant energy. As in the volumes reviewed on a previous occasion, the two new parts are provided with notes on theoretical physics by MM. E. and F. Cosserat.

PROF. H. ERDMANN'S "Lehrbuch der anorganischen Chemie," the fourth edition of which has just been published by Messrs. F. Vieweg and Son, Brunswick, is a comprehensive text-book containing nearly eight hundred pages and three hundred figures. The work presents a concise statement of the present position of inorganic chemistry; it should be of service, not only to students of chemistry, but also to those concerned with the study or progress of other branches of pure and applied science.

A MEMORIAL TO THE LATE PROF. TACCHINI.-From No. 7, vol. xxxv., of the Memorie della Società degli Spettroscopisti Italiani, we are pleased to learn that an international subscription list has been opened for the purpose of founding some lasting souvenir in honour of that great Italian astronomer the late Prof. Tacchini.

A circular letter to this end has, evidently, already been addressed to the members of the society which he founded, and a goodly sum thus realised, but not sufficient to fulfil the object aimed at in a manner worthy of the

occasion.

No doubt the fellow-workers and admirers of Pietro Tacchini, who did so much for the cause of astronomy, will be glad to have this matter brought to their notice, and to help forward the scheme. Subscriptions should be addressed to Prof. L. Palazzo, Directeur du Bureau Central de Météorologie et Géodynamique, Rome.

Report of the PARIS OBSERVATORY FOR 1905.-Although M. Loewy, in opening his report of the work done at the Paris Observatory during the year 1905, mentions that observations were curtailed owing to the preparations for the total eclipse of the sun, the lamented death of M. Paul Henry, the necessary alterations to the principal meridian circle, and other causes, it appears from the report itself that a great deal of work was prosecuted during the

year.

The publications included twenty-seven sheets of the "Cart du Ciel " showing images of 39,697 stars, the ninth part of the photographic atlas of the moon, the second volume of the Catalogue photographique du Ciel," giving the rectangular coordinates of some seventy thousand stars between declination +22° and +24°, and the Annales for 1902.

Two important pieces of work, the determination of the difference of longitude Greenwich-Paris, and the reduction of the magnitudes and positions of the stars in the cluster Messier 3, were completed.

The programme for the current year includes, among other things, the determination of the constant of aberration by M. Bigourdan, the measurement of stellar radial velocities by M. Hamy, and the photographical record of the ionisation of the atmosphere by M. Nordmann.

In any one grain they are piled with perfect regularity, all facing one way, like a regiment of perfectly similar soldiers formed up in rows, where each man is equidistant from his neighbours, before and behind, as well as to right and to left. Or perhaps I might compare them to the welldrilled flowers of an early Victorian wall-paper.

It was shown by Mr. Rosenhain and myself' that when a piece of metal is strained beyond its limit of elasticity, so that permanent set is produced, the yielding takes place by means of slips between one and another portion of each crystal grain. A part of each crystal slides over another part of the same crystal, as you might slide the cards in a pack. It is as if all the soldiers to one side of a given line were to take a step forward, those on the other side remaining as they were, or as if all the men in the front rows took a step to the left, while those in the rows behind kept their places. In other words, the plasticity which a metal possesses is due to the possibility of shear on certain planes in the crystal that are called cleavage" or gliding" planes. Plastic yielding is due to the occurrence of this shear; it may take place in three or more directions in a single grain, corresponding to the various possible planes of cleavage, and in each direction it may happen on few or many parallel planes, according to the extent of the strain to which the piece is subjected. Examine under the microscope the polished surface of a piece of metal which has been somewhat severely strained after polishing, and you find that the occurrence of this shear or slip is manifested on the polished surface by the appearance of little steps, which show themselves as lines or narrow bands when looked at from above. To these we gave the name of slip-bands. Just as the piece of metal is an aggregate of crystal grains, the change of shape which is imposed upon it in straining is an aggregate effect of the multitude of little slips which occur in the grains of which it is made up. Each grain, of course, alters its form in the process.

Speaking broadly, this distortion of the form of any one grain by means of slips leaves it still a crystal. If part of the group of brickbats moves forward, keeping parallel to themselves and to the others, the formation remains regular, except that a step is formed on the outermost rows; the orientation of the elements continues the same throughout. Considerations which I shall mention presently lead to some qualification of this statement. I now see reason to believe that in the process of slip there is a disturbance of the elementary portions or brickbats adjoining the plane of slip, which may alter their setting, and thereby introduce to a small extent some local departure from the perfectly homogeneous orientation which is the characteristic of the true crystal. In very severe straining there may even be a wide departure from true crystalline character. We shall recur to this later; but meanwhile it will suffice to say that substantially the slip which is involved in a plastic strain of moderate amount is a bodily Translation, parallel to themselves, of part of the group of elementary brickbats or molecules which build up the grain. If a crystal the form of which has been altered, even largely, by such straining is cut and polished and etched it appears, under the microscope, to be to all intents and purposes as regular in the tactical grouping of its elements as any other crystal.

66

Further, in the process of straining we have, first, an plastic stage, extending through very small movements, in which there is no dissipation of energy and no permanent set. When this is exceeded, the slip occurs suddenly; the work done in straining is dissipated; if the straining force is removed a strain persists, forming a permanent set"; if it continues to act it goes on (within certain limits) producing augmented strain. In general a large amount of strain may take place without the cohesion between the gliding surfaces being destroyed. Immediately after the strain has occurred there is marked fatigue, showing itself in a loss of perfect elasticity; but this will disappear with the lapse of time, and the piece will then be harder than at first. If, on the other hand, a process of alternate straining back and forth be many times repeated, the piece breaks.

Ewing and Rosenhain, "The Crystalline Structure of Metals," Bakerian Lecture, Phil. Trans. Roy. Soc., vol. cxciii. A, 1899.

These are now familiar facts. Can we attempt to explain them on the basis of a molecular theory which will at the same time offer a clue to the process of crystal-building as we find it in metals? I venture to make this Address the occasion of inviting attention to some more or less speculative considerations which may be held to go some little way towards furnishing the material for such an explanation.

At the Leeds Meeting of this Association, in 1890, it was my privilege to bring forward certain contributions to the molecular theory of magnetism, and to show a model which demonstrated that the rather complex phenomena of magnetisation were explainable on the very simple assumption that the magnetic molecules are constrained by no other forces than those which they mutually exert on one another in consequence of their polarities.' From this were found to result all the chief phenomena of permeability and magnetic hysteresis. Let us attempt to-day to apply considerations of a similar character to another group of physical facts, namely, those that are associated with the crystalline structure of metals and with the manner of their yielding under strain. Just as in dealing with magnetic phenomena, I take as starting-point the idea that the stability of the structure is due to mutual forces exerted on one another by its elementary parts or molecules, and that the clue to the phenomena is to be sought in the play of these mutual forces when displacement of the molecules occurs.

Iron and most of the useful metals crystallise in the cubic system; for simplicity we may limit what has to be said to them. Imagine a molecule possessing polarity equally in three directions, defined by rectangular axes. We need not for the present purpose inquire to what the polarity along the axes is due; it will suffice to assume that the molecule has six poles, three positive and three negative, and that these repel the like and attract the unlike poles of other molecules. We may make a model by using three magnetised rods fixed at right angles to one another at their middle points. I imagine, further, that the molecule has an envelope in the shape of a sphere, which touches the spherical envelopes of its neighbours, and assume that these spheres may turn on one another without friction."

Think now of the process of crystal-building with a supply of such spherical molecules for brickbats. Starting with one molecule, let a second be brought up to it and allowed to take up its place under the action of the polar forces. It will have a position of stability when a positive pole in molecule A touches (or lies in juxtaposition to) a negative pole in molecule B, with the corresponding axes in line, and when the further condition is satisfied that the axes in molecule B the poles of which are not touched by A are stably situated with respect to the field of force exerted by the poles of A.

In other words, we have this formation:

For convenience of representation in the diagram the poles are distinguished by the letters N. and S., but it must not be assumed that the polarities with which we are here concerned have anything to do with magnetism.

Suppose, now, that the crystal is built up by the arrival of other molecules, each of which in its turn assumes the position of maximum stability consistent with formation in

1 "Contributions to the Molecular Theory of Induced Magnetism," Proc. Roy. Soc., vol. xlviii., June 19, 1890, or Phil. Mag, September, 1890. 2 Or, let the envelope be a shell of any form, inside of which the axes of polarity are free to turn as a rigid system.

Along each row the polarity preserves the same direction, but the polarity of each row is opposite to that of each contiguous parallel row. This description applies equally to all three axes. The whole group (Fig. 3) consists of the quartettes of Fig. 2 piled alongside of and also on top of one another. In this way we arrive at what I take to be the simplest possible type of cubic crystal.

In this grouping each molecule has the alignment giving maximum stability, and it seems fair to assume that it will take that alignment when the crystal grain is formed under conditions of complete freedom, as in solidifying from the liquid state. As a rule, the actual process of crystalbuilding goes on dendritically; branches shoot out, and from them other branches proceed at right angles, leaving interstices to be filled in later. We have, therefore, to conceive of the molecules as piling themselves preferably in rows rather than in blocks, though ultimately the block form is arrived at. In this position of maximum stability each molecule has its six poles touching poles of contrary

name.

Now comes a point of particular importance. Imagine two neighbouring molecules in the same block to be turned round, each through one right angle, in opposite senses. They will now each have five poles touching five poles of contrary name, but the sixth pole will touch a pole of the same name as itself. They are still stably situated, but much less stably than in the original configuration, and they will revert to that configuration if set swinging through an angle sufficient to exceed the limited range within which they are stable in the new position.

Similarly we may imagine a group of three, four, or more molecules, each to be turned through a right angle, thereby constituting a small group with more or less stability, but always with less than would be found if the normal configuration had been preserved. The little group in question may be made up of molecules in a row, or it

4444444
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4444444

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4444444

FIG. 3.

may be a quartette or block, or take such a form as a Tor L. A sufficient disturbance tends to resolve it into agreement with the normal tactics of the molecules which build up the rest of the grain.

It is conjecturally possible that small groups of this

kind, possessing little stability, may be formed during the process of crystallisation, so that here and there in the grain we may have a tiny patch of dissenters keeping one another in countenance, but out of complete harmony with their environment.

If this happens at all during crystallisation, it would seem less likely to happen in free crystallisation from a liquid state than in the more constrained process that occurs when a metal already in the solid state recrystallises at a temperature far below its melting-point. Though rare or absent in the first case, it might occur frequently in the second. There are differences in the appearance of crysta grains under the microscope in metal as cast and in metal as recrystallised in the solid state, of which this may be the explanation. It may also explain a difference pointed out by Rosenhain,' that the slip lines in cast metal are straight and regular, whereas in wrought iron and other metals which have recrystallised in the solid they rarely take a straight course across the crystal, but proceed in jagged, irregular steps. These may be due to the presence here and there of small planes of weakness, resulting from the existence of what I have called dissenting groups. Again, these groups, possessing, as they do, less stability than their normal neighbours, may be conjectured to differ from the normal parts of the grain in respect of electrolytic quality, and to be more readily attached by an etching reagent. Hence, perhaps, the conspicuous isolated geometrical pits that appear on etching a polished surface of wrought iron.

It will help in making clear these points, and others that are to follow, if we study the action of a model formed by grouping a number of polarised "molecules" in one plane, supporting them on fixed centres, about which they are free to turn. In the model before you the centres are uniformly spaced in rectangular rows, and the "molecules" are shaped pieces of hardened steel, strongly magnetised along each of the crossed axes, each having, therefore, two north poles and two south poles. The third axis is omitted in the model, the movement to be studied with the help of the model being movement in one plane. On placing these "molecules "on their centres they readily take up the position already indicated in Fig. 3. Each one within the group has its four poles in close proximity to four poles of contrary name, and is, therefore, highly stable. If disturbed by being turned through a small angle, and let go, it swings back, transmitting a wave of vibration through the group, which is reflected from the edges, and is finally damped out in the model by pivot friction and air friction. We may assume some damping action (say by the induction of eddy-currents) in the actual solid, of which the model may be taken as a very crude representation.

By turning two molecules carefully round together, each dissenting pair, the equilibrium of which has feeble stability. through one right angle in opposite senses, we set up a A slight displacement, such as might be produced by the transmission of a vibrational wave, breaks them up, and they swing back to the normal configuration, giving out energy, which is taken up by the rest and is ultimately dissipated. By making the dissenting coterie consist of three or more we can give it additional strength.

An example is shown in Fig. 4, where the three molecules marked a, b, and c are turned round in this way.

Notice that the normal molecule d, adjoining a line of such dissenters, is in a peculiar position. His neighbours present to him three N. poles and one S. pole. He has the choice of conforming to the majority, or of throwing in his lot with the dissenters; and he has a third possible position of equilibrium (very feeble equilibrium) which is reached when his two S. poles are turned until the one neighbouring south pole faces just between them. I have laboured these points a little because they seem important when we come to speak of the effects of strain.

Consider now the straining action, which we may imitate in the model by sliding one part of the group past the other part. For this purpose the centres are cemented to two glass plates which can slide parallel to one of the

axes.

1 Rosenhain, "The Plastic Yielding of Iron and Steel," Jour. Iron and Steel Institute, No. 1 for 1904, p. 335.