Thornycroft, with his turbine propeller, is able to emphasize this economy of weight still further, and, but for difficulties of going astern not yet surmounted, would be able to save considerable weight and space in sea-going steamers with this contrivance.

As regards their construction, turbines are divided into three classes (p. 24)—the radial, axial, and mixed-flowaccording to the mode in which the water enters and passes through the turbine; but as regards the dynamical principle on which the turbines work, they are divided into two classes (p. 25), the reaction and the impulse turbine.

In the reaction or Jonval turbine, described in chapters iii. to vi., the passages are completely filled with water, and the changes of pressure play an important part in the work performed. This turbine possesses the advantage of being able to work when drowned by the tail race, or when elevated above the tail water to a height anything less than the height of the water barometer, a suction tube of properly adjusted shape being fitted below the turbine to carry off the water at pressure gradually increasing downwards to the atmospheric pressure. Against this are the disadvantages of imperfect regulation for varying load, and that with a high fall this turbine must be made so small and must run so fast as rapidly to wear out, as in the Fourneyron turbines at St. Blaise (p. 422); but this disadvantage the author professes (p. 263) to avoid by compounding the turbine, just as we compound the steam-engine with high-pressure steam.

The impulse or Girard turbine, on the other hand (chapters vii. and viii.), derives its power entirely from the change of momentum of the water without change of pressure; the buckets are freely ventilated, and consequently this turbine can only work in communication with the surrounding air. It possesses, too, the great advantage of complete regulation of power by merely altering the supply of water. Girard turbines are divided into outward flow (Fourneyron) turbines, and inward flow (James Thomson); the latter, although more weighty and costly, possessing the advantage of greater stability of motion.

In their difference of action we may compare the Jonval turbine with the screw propeller, which works entirely immersed, and derives its reaction partly from the change of pressure in the water; while the Girard turbine resembles the paddle-wheel in working at the surface of separation of the water and air, so that no appreciable change of pressure is manifest. Against this analogy, however, we find the screw propeller far less susceptible to changes of immersion than the paddlewheel, whence the manifest superiority of the screw for long voyages.

In chapters ix. to xi. the author gives a very valuable collection of numerical applications of his theories to actual turbines on a large scale. In designing a turbine to utilize a fall, the first important measurement is that of the quantity of the stream of water; the speed of the turbine is next determined from the consideration that the best theoretical speed is half (or a little more than half) the speed at which the turbine would run if unloaded; and then various practical considerations intervene in deciding whether the turbine should be reaction or impulse, outward, inward, or mixed flow.

At Holyoke, Mass., the Water-Power Company, under Mr. James B. Francis, controlling the falls of the Connecticut, undertake the commercial testing of turbines submitted to them, and have checked to some extent the wild claims of efficiency, reaching and even exceeding 100 per cent., which American turbine makers are said to have claimed in their advertisements. There is still, however, an efficiency claimed for American turbines which has not been rivalled in Europe. this cannot be attributed to defect in our designs, and the author thinks must be attributed to the less care bestowe i in America on the measurement of the quantity of water consumed. It is noticeable that the American turbines are generally of the reaction Jonval type, which is more suitable for their unlimited supplies of water by reason of its smaller weight and cost; here in Europe, where water is scarcer, the impulse Girard turbine is more in favour

For mining purposes, especially in California, with great falls of 400 or 500 feet and small quantities of water, the hurdy-gurdy or Pelton wheel (p. 419) is a favourite, and in a paper by Mr. Hamilton Smith, Jun., of the American Society of Civil Engineers, the efficiency of this wheel and its practical advantages are declared to be very high. Similar small impulse turbines seem likely to come into general domestic use.

The author concludes (chapter xiii.) with a description of the various hydraulic pressure engines and motors of Armstrong, Rigg, and others. These engines act by pressure only, like the steam-engine, with the disadvan!age of using the same quantity of water whether working at high or low power, except in the case of Mr. Rigg's motor. Such motors are, however, coming into great use on ships, not only for working the guns, but for steering, loading, and discharging cargo.

Although designed, and amply fulfilling its purpose, as a practical treatise on hydraulic motors, this book will provide the pure theorist with some of the most elegant applications of relative velocity, aberration, dynamical principles, and of hydromechanics; and it is instructive to notice that, as in all practical mechinical treatises, gravitation units of force only are employed, even in the hydrodynamical equations of Borda and Carnot, or of Bernoulli, as we think they should be called. All this is in direct opposition to the theoretical text-books; theorist or practical man, which is to give way? !

THIS

A. G. G.

PHYSIOLOGY OF EDUCATION.

Physiological Notes on Primary Education and th Study of Language. By Mary Putnam Jacobi, M D. (New York and London: G. P. Putnam's Sons, 1889. HIS is a remarkable book. The authoress is an original thinker who knows how to express her thoughts clearly and strongly. It is worthy of being read by all interested in the science of education, though few perhaps even of the advocates of the present educational renaissance would be prepared to receive every one of her conclusions.

The work consists of four distinct essays. The first two are entitled "An Experiment in Primary Education," and describe the way in which Dr. Mary Jacobi taught

her own little girl. She commences the account with some very valuable remarks on the right order of studies.

"The first intellectual faculties to be trained are perception and memory. The subjects of the child's first studies should therefore be selected, not on account of their ultimate utility, but on account of their influence upon the development of these faculties. What sense is there then in beginning education with instruction in the arts of reading and writing?... From the modern standpoint, that education means such an unfolding of the faculties as shall put the mind into the widest and most effective relation with the entire world of things-spiritual and material, there is an exquisite absurdity in the timehonoured method. To study words before things tends to impress the mind with a fatal belief in their superior importance."

As forms and colours are the elements of all visual impressions, Dr. Jacobi began to teach her child geometrical forms before she was four years of age. At four and a half the little girl began elementary colours. Afterwards she made acquaintance with the points of the compass, the main ideas of perspective, and then maps and geography. The study of number, of course by concrete illustrations, followed that of form and outline. The observation of natural objects, especially that of plants and plant-life, was then commenced. The growth of beans and hyacinths was carefully watched, and the daily observations made by the child were written down by the mother, till she attempted them herself, and became gradually initiated into the mysteries of writing. This led her on easily to the art of reading when she was about Six years of age. The progress of the child's mental development during these early years is fully described, with many pleasant recollections of her sayings.

The third part consists merely of a criticism of Miss Youman's views on the teaching of botany, and an argument in favour of commencing in a child's education

with the flower rather than the leaf.

Half the book, however, is occupied by the fourth essay, in which the authoress treats of " The Place for the Study of Language in a Curriculum of Education." Of course she places it after the mind has been trained to deal with sense perceptions of external objects; but she contends earnestly for the importance of the study of words, especially for the power it possesses of enabling the child to form abstract conceptions. The authoress enters largely into the brain action involved in the use of verbal signs or complex ideas, and illustrates her views of the matter by means of physiological diagrams. She also describes a little device for the comparison of verbal roots, which she terms "language tetrahedrons," and which are intended to show the relation between Latin, French, German, and English. She would devote to literary studies, including English, the best part of the time between the Kindergarten training and the age of fourteen.

"To the study of words may be brought the scientific methods used in the study of things-observation, analysis, comparison, classification; and the child may thus begin to be trained for physical science at a time when the pursuit of most physical sciences is impossible."

It may be that Dr. Mary Jacobi claims too much time for the study of language, but the old-fashioned educationalists will get little consolation from her concessions; for she not only places the study of words after that of things,

Steam-Engine Design. By Jay M. Whitham, Professor of Engineering, Arkansas Industrial University. (London: Macmillan and Co., 1889.)

IN this work the author treats of the application of the principles of mechanics to the design of the parts of a steam-engine of any type or for any duty. He acknowledges that he has culled as much information as he has required from well-known sources, both English and American; and he has embodied, as a sort of foundation for his work, a course of lectures given to his class at the United States Naval Academy by P.A. Engineer John C. Kafer, U.S.N.

After careful study, we can say that the book appears to be well suited for its purpose. The arrangement of information, both principles and details, is much the same as that in Mr. A. E. Seaton's excellent work on marine engineering; but the field covered is of far less extent, and the boiler and its accessories are not included. The author being a Professor of Engineering in an American University, we expected to find some variations from our own practice in steam-engine design. In this, however, we were disappointed. A few of the woodcuts from those used in this country, but the main design is represent parts of engines differing in insignificent details. practically the same. It is gratifying to find many of our own engineers quoted as authorities in the volume-viz. D. K. Clark, A. E. Seaton, R. Sennett, and many other well-known English authorities.

It must not be supposed that there is no original work in this book. Chapters ii. and iii. for instance, on the design of slide valves and reversing gears, are ample evidence of hard work on the part of the author: his descriptions and diagrams of the various motions are excellent. Chapter iv. deals with the general design and proportions of the steam-chest, valves with their various connections. Chapters v. and vi. are on compound and triple-expansion engines, and contain also a theoretical treatment of indicator diagrams of a compound engine. These chapters are well written, and contain much useful information, but as a whole they do not teach anything gineer Asa M. Mattice, U.S.N., the same remarks will new. To chapters vii. and viii., written by P.A. Enapply. The remaining chapters deal with the design of the various other parts of a steam-engine. The methods used are those well understood in every drawing-office worthy of the name, and they need not be further noticed here.

Taken as a whole, the book deserves praise for good and careful work; and we may especially call attention to the theoretical considerations, which are always clearly expressed. Although published by Messrs. Macmillan, the work is from an American press, that of Messrs. Ferris Bros., New York. The printing and woodcuts are excellent- far better, as usual, than English work of the same class. N. J. L. Coloured Analytical Tables. By H. W. Hake, Ph.D., F.I.C., F.C.S. (London: George Phillip and Son, 1889.) NOVELTIES in text-books of elementary qualitative analysis are usually conspicuous by their absence, but the

book before us takes an entirely new departure. The idea of representing the various coloured reactions by tinted imitations is, so far as we know, quite new. Apart from this, the usual well-worn paths are followed. The tables are of the simplest character, and are only sufficient for the detection of common bases in salts or oxides, no attempt being made to separate the members of the various groups. The second part is devoted to reactions for the detection of a few acids and organic substances. The book is apparently primarily intended for the use of students preparing for the preliminary examination of the Conjoint Board of the Royal College of Physicians and Surgeons, but it will no doubt have a much wider field of usefulness if it survives the test of experience. The new method of representation seems excellently adapted for young students, and certainly no harm can be done by giving it a fair trial.

The reactions illustrated include precipitates, charcoal reactions, borax beads, and flame colorations, most of which are fairly well represented.

The Story of a Tinder Box. By Charles M. Tidy, M.B. M.S., F.C.S., &c. (London: Society for Promoting Christian Knowledge, 1889.)

POPULAR lecturers have discovered for some time that the history of the methods that have been used for obtaining a light is an excellent subject wherewith to please the public mind, and this book contains the reports of three such lectures delivered to a juvenile auditory last Christmas. An attempt has also been made to describe the experimental portion of the lectures, and the author has not committed the common error of giving a multiplicity of pretty but irrelevant experiments conveying a paucity of information. In fact, in some parts the reverse seems the case, for we must confess our inability to discover why a consideration of the allotropic modifications of carbon should necessitate a detailed description of the manufacture of black lead pencils. This digression, however, does not detract from the interest and general merit of the work, which certainly contains the explanation in simple language of some elementary physical and chemical phenomena.

Magnetism and Electricity. Part I. Magnetism. By Andrew Jamieson, M.I.C.E. (London: Griffin and Co., 1889.)

ALTHOUGH elementary text-books of physics continue to increase in number, there is still room for one of such general excellence as Prof. Jamieson's elementary manual. The book is specially arranged for the use of first year Science and Art Department and other electrical students. Numerous questions and specimen answers are distributed throughout the book, and though this may be rather suggestive of cram, there is nothing in the text to justify such a suggestion. It is unnecessary to go into details, but it may be stated that the arrangement of subjects is as good as it well can be, and on the whole the descriptions are very clear. The numerous diagrams are also excellent, those of the mariner's compass being especially good; indeed, the whole chapter on terrestrial magnetism is the best elementary account of the subject which has come under our notice.

The subject is throughout considered as an essentially practical one, and very clear instructions are given for the making of magnets, and compass and dipping needles. If the succeeding parts of the book confirm the good opinion created by the first, teachers of the subject are to be congratulated on having such a thoroughly trustworthy text-book at their disposal.

Time and Tide: A Romance of the Moon. By Sir Robert S. Ball, LL.D., F.R.S. (London: Society for Promoting Christian Knowledge, 1889.)

THE ability of the author of this work to give a lucid exposition of an abstruse subject is a matter of common

knowledge; and hence the fact that the book contains two of his lectures delivered at the London Institution las November is in itself sufficient commendation. However, be this as it may, we have no hesitation in saying there could hardly be a clearer explanation of Prof. George Darwin's theory of tidal evolution than that contained in the work before us. The hypothesis being accepted, ever v feature of the past and future condition of our satellite is described in a most comprehensive manner. It is first shown how, when the earth was rotating on its axis with an enormous velocity, the tidal action set up by the sun caused a portion to become detached and form our satellite. The employment of the term "conservation of spin "facilitates considerably the demonstration of the fact that as by tidal action the spin of the earth decreases-as our day lengthens-so must the dimensions of the moon's orbit be increased, and the length of the month therefore become proportionally greater. The ap plication of Prof. Darwin's theory to other members of our system is also inquired into ; and although the author does not attempt to go back to the first stage in the evolution of celestial species, he shows that tidal evolution is an extension of the hypothesis that does so. Indeed, scientific reader will be found exceedingly interesting. the book is replete with information, and by the general

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertak to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURI, No notice is taken of anonymous communications.]

Specific Inductive Capacity.

PERHAPS a better mode of performing the experiment quotes! by Mr. Rudge (p. 10) is to have two insulated parallel metal plates, one connected with an electroscope, the other with a of paraffin or ebonite (recently passed through a flame) between slightly-charged Leyden-jar. On now interposing a thick slab the plates, a very decided increase of divergence will be per ceived. Unless, indeed, the electroscope should happen to have overflowed to earth during the charging of the jar, in wh.d case it will be oppositely charged and a decreased divergence may be caused. To interpose the slab is, in fact, virtually to diminish the distance between the plates, and its effect is there fore the same as that of pushing the plates closer together.

The advantage of the Leyden-jar is that it keeps the potentia' practically constant. If an isolated plate or sphere is used as the charged body the circumstances are not so simple; for the insertion of the slab reduces the potential and slightly increases the charge on the near face of the plate, so that whether the divergence of the leaves is increased or diminished depends on several unimportant considerations, of which the size of the slab may be one. A slab of area comparable to that of the plates between which it is put would in this case be the most suitable; and in any case it should be supported by a long insulator, so and mask the effect. that the operator's arm, as it approaches, shall not complicate OLIVER J. LODGE.

University College, Liverpool, November 9.

"La Pietra Papale."

ABOVE Stresa, on the western bank of Lago Maggiore, there is an enormous granite boulder, which deserves the attention of

geologists. It lies on the left slope of an old moraine, near the little village of Gignese, and not far from the Hotel Alpino, al an elevation of about 2500 feet above the sea-level. It is roughly oblong in shape, and measures some 75 feet in length, and perhaps half as much in breadth and thickness. The projected mountain railway from Stresa to the summit of Monte Motterone will pass close to the spot where it lies, and the masons are already engaged in converting the smaller boulders into buildingstones. It is to be hoped, however, that la pietra papali as this splendid example of the carrying powers of ice is

Who discovered the Teeth in Ornithorhynchus ? As Dr. Hart Merriam's letter on the above subject in your issue of the 7th inst. (p. 11) will be read by many who have not access to Sir Everard Home's "Lectures on Comparative Anatomy," allow me to point out that the description and figures in that work referred to by Dr. Merriam have no bearing whatever upon the very interesting discoveries recently made. They represent, not the real teeth of the young animal discovered by Mr. Poulton, and fully described by Mr. Oldfield Thomas, but the well-known horny plates which functionally take their place in the adult, and which are called "grinding teeth" by Sir Everard only in a very general sense.

W. H. FLOWER.

British Museum (Natural History), November 9.

THE account of the teeth of Ornithorhynchus, given by Sir Everard Home in "Lectures on Comparative Anatomy," vol. i. P. 305, explanatory of Tab. lix. vol. ii., referred to by Mr. Hart Merriam in your last issue (p. 11), shows, even more clearly

than the figures, that the true teeth had not been noticed at that time (1814). The passage is as follows:-" In the posterior portion of the mouth, both in the upper and lower jaw, are placed grinding teeth with broad flattened crowns, four in number, one on each side of each jaw. They are composed of a horny substance (the italics are my own), only embedded in the gum, to which they are connected by an irregular surface in the place of fangs. When cut through, the substance appears fibrous, like that of nail; the direction of the fibres being perpendicular to the crown, similar to that of the horny crust of the gizzard. The teeth in the young animal are smaller, and two on each side, so that the first teeth are probably shed, and the two small ones replaced by one large one.'

It is perfectly evident that here no reference is made to the true teeth, and, moreover, the figure of the two smaller "teeth" of young specimens represents merely the immature horny plates. The honours, therefore, still remain with Mr. Poulton and Mr. Oldfield Thomas. OSWALD H. LATTER. Anatomical Department, The Museum, Oxford, November 8.

On a Mite of the Genus Tetranychus found infesting Lime-trees in the Leicester Museum Grounds. ABOUT the 13th of last September my attention was called to the strange appearance of a row of lime-trees standing in front of the School of Art buildings in Hastings Street. On examination I found that the whole row, with, I think, only one exception, were almost entirely devoid of leaves, the trunks and branches being covered with a fine web, very closely spun, giving them the appearance of being coated with a thin layer of ice, this glazed look being specially noticeable when standing in such a position as to catch the reflected rays of the sun. At first sight I imagined that I was examining the work of a spider, though I was unable to recollect any whose webs would accord with the character of those under observation. However, a close inspection revealed the webs to be tenanted by an innumerable number of yellowish or orange-coloured mites which were in some places associated together in dense masses or clusters, and more or less abundant over the whole of the trunks and branches.

"red

These mites appeared, on being subjected to a careful microscopical examination, to be identical with Tetranychus tiliarum, Mull., a species which it seems that Claparède considers to be only a variety of T. telarius, the common spider." However that may be, they are at any rate closely allied forms-members of the family Trombidiida, which pos sess, as one of their distinguishing characteristics, a pedipalpus with a claw and a lobe-like appendage. In the genus Tetranychus the palpi are chelate, the mouth is furnished with a barbed sucking apparatus for the extraction of plant juices, and spinning organs are usually present. It is needless to comment upon their destructiveness to vegetation, for most keepers of gardens and hothouses are familiar with their ravages in one

direction or another, and the difficulty experienced in thoroughly extirpating them.

In connection with the species which forms the subject of the present communication, I notice that Murray, in his work on the "Aptera," says: "It occasionally occurs in such numbers as almost to denude the trees of their foliage; and it has been noted that the stems and branches of such trees seemed covered with a bright glaze. Can this be a fine web?" It was so, most certainly, in the present instance, which afforded me a most favourable opportunity for examination. Again, it appears that the mites are normally found on the under-surface of the leaves, which they cover with a fine web of silk, on which (to again quote Murray) "they are sometimes crowded together in vast numbers; for example, we have seen them so thick on the leaves that they looked as if they were not merely sprinkled with a yellow orange coloured powder, but as if it was actually in parts heaped up on them, so that none of the green colour of the leaf was visible." Their presence is of course highly injurious, causing the leaves to shrivel and drop; and it seems to me that the fact of their occurrence on the bare bark of the trunks was attributable to the death of the leaves causing them to retreat to that position, uncongenial though it would seem to be. Such trees as preserved their foliage presented no abnormal appearance on the branches, &c., notwithstanding which, in one or two instances, I believe the parasites were present on the leaves, though seem

ingly not in such extraordinary profusion.

Duges, writing of T. telarius, states his belief that that species passes the winter under stones, and instances the finding of several active individuals so situated in a garden near Paris in the month of October. Regarding this point I may say that my

specimens of 1. tiliarum, which I placed in a box immediately after removal from the trees, speedily ensconced themselves in the most convenient nooks and crannies, in which they spun fine webs. It may be worth noting that the days on which my observations were made were warm and damp, with scarcely any wind, quite typical early autumn days in fact.

Leicester Museum.

Retarded Germination.

F. R. ROWLEY.

I SHALL be much obliged to any of your readers who can give an explanation of the probable cause of the above phenomenon, which I have remarked this year. I sowed a number of patches of seeds of various hardy annuals in the garden in the last week of April; about half of them came up after the usual interval, strongly and regularly. Such were Calendula Pongei, Convolvulus minor, Lavatera trimestris, Collinsia bicolor, Iberis white and red, Specularia speculum, Linum rubrum, &c., &c. Then there were some of which a few scattered seedlings made their appearance at this time, and after an interval of about six weeks the greater part of them also came up ; among these were Eutoca viscida, Nigelia damascena, Sphenogyne, and Clarkia pulchella. Thirdly, there were some of which I quite despaired; mignonette, however, appeared thinly about the end of June, and at intervals till August; and in the middle of June a few plants (in proportion to the seed sown, a few) of Linaria bipartita, Madia elegans, and Xeranthemum came up one consequence being that the last named has not yet flowered. Some of the seeds were obtained this spring from seedsmen, some were my own collection of the last year or two-of the latter were Calendula, Lavatera, Convolvulus, Specularia, Eutoca, Nigella, Sphenogyne, and mignonette-so that cannot be said to give any clue. The conditions for germination and growth were favourable, and the season also. I have never remarked before any annuals so long in appearing above ground; though in some herbaceous plants I have noticed it, e.g. Gaillardia, Myosotis alpestris, and Anemone coronaria. E. A.

Herefordshire, September 19.

The Relation of the Soil to Tropical Diseases. As a humble subscriber to and student of NATURE, will you bear with me while I ask your help, as shortly and plainly as I can? I am in a very secluded corner of one of the Native States of Rajpootana, and I am collecting facts and making observations on the relation of the soil to tropical diseases; my ambition being to discuss it not so much from a statistical and geographical standpoint, as from the geological, in its chemical and biological

aspects; though, as I conceive, the geographical, climatological, and geological elements in the problem are not to be arbitrarily distinguished. Now I am far away from all books of reference, and it is of course essential that I make myself acquainted with what has already been done in these subjects, and I venture to ask for any hints as to the bibliography of them. Can you tell me if anyone has done for geology what Hirsch, of Berlin, has done for geography (in his work on the distribution of disease)? Is there any authority on the chemistry of soils, and what I roughly call their physiology and pathology, their structural and functional changes under influences-climate notably and their own intrinsic, and the deeper geological interactions? A. ERNEST ROBERTS. Meywar Bheel Corps, Kherwara, Central India, September 9.

The Earthquake of Tokio, April 18, 1889.

DR. VON REBEUR-PASCHWITZ'S letter, which appeared in NATURE, vol. xl. p. 294, is of special interest to us in Japan, countenancing as it does the conjecture that the very peculiar earthquake felt and registered here on April 18 was the result of a disturbance of unusual magnitude. It was my good fortune on the day in question to be engaged in conversation with Prof. Sekiya in the Seismological Laboratory at the very instant the earthquake occurred. We at once rushed to the room where the self-recording instruments lay, and there, for the first time in our experience, had the delight of viewing the pointers mark their sinuous curves on the revolving plates and cylinders. At first sight it seemed as if the pointers had gone mad, tracing out sinuosities of amplitudes five or six times greater than the greatest that had ever before been recorded in Tokio. There was not much sensation of an earthquake; indeed, after the first slight tremor that attracted our attention, we felt nothing at all, although in the irregular oscillations of the seismograph pointers we had evidence enough that an earthquake was passing. Very few in Tokio were aware that there had been an earthquake till they read the report of it in the next day's papers. Thus the motion, though large, was too slow to cause any of the usual sensations that accompany earthquakes, and suggested a distant origin and a large disturbance, with a consequent wide extension of seismic effect. Excepting the slight remors recorded at Potsdam and Wilhelmshaven, there has been, so far, no evidence of any such far-reaching action.

My object in writing this note, however, is to correct an error of calculation which Dr. von Rebeur-Paschwitz has unwittingly made. He has assumed that Tokio standard time is mean local time. On the contrary, the standard time for all Japan is the mean solar time for longitude 135° E.,-that is, nine hours in advance of Greenwich mean time. Hence, instead of the Tokio earthquake having preceded the German disturbance by 1h. 4'3m. it preceded it by only 45m. This correction increases the velocity of transmission to 3060 metres per second. We must assume, then, either that large disturbances in the heart of the earth travel with exceptionally high speeds, or that the origin of the disturbance was a considerable distance from Tokio. The latter assumption seems sufficiently satisfactory, if in other respects Dr. von Rebeur-Paschwitz's views meet with approval. CARGILL G. KNOTT. Imperial University, Tokio, Japan, September 25.

A Brilliant Meteor.

YESTERDAY evening, November 4, at 7.55 p.m., I was for. tunate enough to observe a very brilliant meteor. It became visible almost exactly at the zenith, or a little west of it, and moved, as nearly as I could judge, due east, magnetic; it remained visible for about from one to two seconds, disappearing, finally, rather low down on the eastern horizon. For the first half of its journey it was of a dazzling white brightness, and then it suddenly became a dull red spark. The light emitted from it when brightest reminded me of the light from an arc lamp, and was very much brighter than any of the fixed stars.

As it was so short a time in view, and there were no stars visible, I could only approximately estimate its point of appearance and path. There were a few clouds about, mostly in the west, and the moon was behind them. PAUL A. COBBOLD. Warwick School, November 5.

ON THE HARDENING AND TEMPERING OF

STEEL

II.

THE following considerations appear to have guided Osmond in beginning his investigations (see ante, p. 16). Bearing in mind the fact that molecular change in a body is always accompanied by evolution or absorption of heat, which is, indeed, the surest indication of the occurrence of molecular change, he studied with the aid of a chronograph what takes place during the slow cooling and the slow heating of masses of iron or steel, using, as a thermometer to measure the temperature of the mass, a thermo-electric couple of platinum and of platinum containing 10 per cent. of rhodium, converting the indications of the galvanometer into temperatures by Tait's formulæ.

FIGS. 5 and 6 show the actual mode of conducting the experiments. F(Fig. 5) is a piece of steel into which a platinum and platinum-rhodium couple, t, f, is fixed. It is inclosed in a glazed porcelain tube and heated to bright redness in the furnace, s (Fig. 6). This tube, T, may be filled with any gaseous atmosphere. c is a bulb filled with chloride of calcium. The metal under examination is slowly cooled down. The wires from the thermo-couple pass to the galvanometer, G. The rate of cooling of the mass is indicated by the movement of a spot of light from the galvanometer mirror at, on the screen, R, and is recorded by a chronograph. The source of light is shown at L; M is a reflector.

In the next diagram (Fig. 7) temperatures through which a slowly-cooling mass of iron or steel passes, are arranged along the horizontal line, and the intervals of time during which the mass falls through a definite number (66) of degrees of temperature are shown vertically by ordinates. See what happens while a mass of electro-deposited iron (shown by a dotted line), which is as pure as any iron can be, slowly cools down. From 2000 to 870° it falls uniformly at the rate of about 2'2° a second, and the intervals of temperature are plotted as dots at the middle of the successive points of the intervals. When the temperature falls down to 858°, there is a sudden arrest in the fall of temperature, the indicating spot of light, instead of falling at a uniform rate of about 2° a second, suddenly takes 26

A Lecture delivered on September 13, by Prof. W. C. Roberts-Austen, F.R.S., before the members of the British Associatica. Continued from P. 16.