The illustrations are also unusually good in both books, but while Wernicke's is professedly a mathematical treatise, the work of Buff leans more to the physical aspects of mechanics. There is, however, considerable reference to mathematics in Buff, in fact, he makes free use of the calculus when necessary.

The book consists of thirteen sections :-Section I. is on Rest and Motion; Section II. on Movement in Space and Time: this contains, in addition to the usual theorems on the motion of a point, a useful article on harmonic motion. Section III. introduces the Composition of Movements; in this will be found a discussion of experiments upon the trajectory of the bullet from the needle-gun. Section v. commences the subject of Mechanical Work; we are glad to see in this book the principle of work receives that prominence which it unquestionably deserves. Section VII., on Friction, discusses, among other subjects, Pambour's experiments upon the friction of railway carriages. Section IX., upon the Efficiency of Machines, is admirable, the theory being properly proportioned to the experiments. We find here a full discussion of the subject, without that deluge of formula which is so often repulsive to those in search of distinct physical conceptions. Section X. contains what is familiar to us by the term Mechanism; Section XII. is the most complete account of Centrifugal Force which we have met with in any work; we have here a physical explanation of the permanent axes, of precession and nutation, of the mode of finding the masses of the heavenly bodies, and of various other matters. Section XIII., upon the Motion of the Pendulum, is a collection of interesting subjects, among them Foucault's pendulum, and a far better account of Cavendish's experiments than is to be found in any English book on mechanics. We are also a little surprised to find the weighing scales treated in this section. The arrangement is novel, and though doubtless much might be said in favour of it, yet we think, on the whole, it is not convenient.

We cordially recommend Buff's treatise to the notice of teachers of natural philosophy.

Mr. Wormell's book, which appears to have been specially intended for the London University examination for B.A. and B.Sc., contains practical and experimental illustrations, in addition to the usual matter. We should

gladly welcome a thoroughly good work on the general plan which has been adopted by Mr. Wormell, but the book before us ought to receive careful revision before it is placed in the hands of students. We shall indicate some of the points that we have noticed which require

correction. We do so in the belief that a future edition of the work might be made really valuable, and supply a much felt want. Some of the errors are common to this work and other text-books. We can, therefore, only accuse Mr. Wormell of reproducing them, but we cannot allow this excuse on every occasion.

On page 14, we find as follows:-"Any two forces F', F' applied at a point M may be transferred parallel to themselves to any other point M' in the line of direction of the resultant."

This proposition, if true, would assert that the attractions of the earth and sun upon the moon might be transferred to any heavenly body in space which happened to be in the line of direction of the resultant of the forces. The geometrical proof of the composition of parallel forces (p.

33) is meaningless, until the proposition referred to has been properly stated. This blunder is extremely common, it arises from enunciating as a property of forces what is really the definition of a rigid body.

On page 112 we find the following passage :—

"1. When the materials composing the surfaces in contact remain the same, the friction varies as the pressure. Suppose, for example, that a block of wood, having a hole bored in it, rests on a plane inclined at the angle of repose, if lead be poured in the hole, the screw may be turned so as to incline the plane at a greater angle without causing the body to slide. By increasing the pressure

we increase the friction."

This is very bad; the statement we have italicised in the second paragraph is entirely erroneous. So serious an error would be quite inexcusable even in one of those for whose use the book has been written.

We should have liked to have seen more experiments upon the mechanical powers cited. A student who reads (p. 94) that in the three sheave pulley-block the power is one-sixth of the load, will naturally be surprised when he finds by trial that the power must be one-fourth of the load; nor can we find a single word in the book which would enlighten his difficulty. We should also have expected that the author would have replaced the antiquated and useless pulley systems which only exist in manuals, by some compact and useful machines like the differential pulley.

Such are some of the points which we consider to require careful revision before Mr. Wormell's book can be pronounced suitable for the use of students.

OUR BOOK SHELF

Contributions to Botany, Iconographic and Descriptive. By John Miers, F.R.S., F.L.S. Vol. 3, containing a complete Monograph of the Menispermaceæ. Sixtysix litho plates. (London: Williams and Norgate, 1864-1871.)

Mr.

MR. MIERS's long-promised Monograph of the Menispermaceæ forms the third volume of his valuable "Contributions to Botany." The intimate acquaintance of this veteran botanist with South American plants, and his than twenty years, render his observations peculiarly long study of this particular family, extending over more valuable to all systematic botanists. Although in some important particulars Mr. Miers combats the views of such high authorities as the authors of the "Flora Indica," and those of the "Genera Plantarum," he adduces reasons for his dissent, which will, at least, need careful consideration from all who hereafter write on these plants. Miers retains, with some modifications, his views of the structure of the different organs in this order published in the Annals of Natural History in 1851, and classifies the genera which constitute it into seven tribes, on characters dependent mainly on the structure of the fruit, and on the position of the cotyledons relatively to the radicle, whether incumbent or accumbent. The establishment of sixty-four distinct genera in the order, instead of the thirty-one admitted by Bentham and Hooker, may be open to criticism, but several of them contain only single species now for the first time described, which appear to be altogether aberrant types of the order. Good plates are always valuable; and we have here sixty-six, drawn on stone by the author himself, containing careful dissections to illustrate the salient characters of the genera and more important species. This concluding volume of Mr.

Miers's "Contributions to Botany" is no less valuable than any of its predecessors as a record of laborious and conscientious devotion to science. A. W. B. An Elementary Treatise on Statics. By J. W. Mulcaster F.R.A.S., Military Tutor. (London: Taylor and Francis.), THIS is a good book without any of that attempt at cramming, too common now in our elementary text-books. It is calculated to give the reader a good grasp of the elements of Statics. It goes over the usual ground, states and proves the principles well and clearly, and contains in each chapter a numerous and excellent series of examples. These examples consist of "graduated and classified groups of problems, each involving distinct statical principles." These, the author says, he finds, and our experience entirely agrees with his, make “an impression on the student's mind otherwise not attainable with problems indiscriminately taken." We gather from the book that it is the production of a good and practical J. S.

teacher.

LETTERS TO THE EDITOR

[The Editor does not hold himself responsible for opinions expressed by his correspondents. No notice is taken of anonymous communications.]

The Aurora Borealis of Nov. 9 and 10

As the magnificent display of Aurora on the evening of the 10th was witnessed here under very favourable circumstances, and as several of its phases were of unusual occurrence, an abridged account may not be uninteresting.

The Northern Lights were first noticed at about 7.30 G. M. T.. the appearance being that of a pale white light, which gradually rose from the N.N. W., until it completely enveloped the Great Bear, but was not sufficiently strong to hide even the faint star near Mizar. Towards 8.40 the auroral mist assumed the more definite form of three broad white bands, stretching across the sky from E. to W., the uppermost band lying just below Vega

and Pollux.

At the same time a bank of dense black cloud rose from the N. horizon to the height of ŋ Ursæ, and shot forth dark streamers n as far as the upper arch of light, The streamers E. and W. were brighter than the central part, and waves of light moved slowly and at regular intervals from these brighter parts of the horizon, mingling together at the centre of the arch.

At 9.10 a very bright streamer made its appearance.

ON Friday evening, Nov. 10, I was fortunate enough to witness a brilliant display of the Aurora Borealis, which, if it did not surpass, certainly rivalled, that of Oct. 24, 1870.

At 9h. 20m. G. M. T. the whole sky was literally covered with rently converging to a point near a Andromeda. auroral streaks to within 30° of the southern horizon, all appaThe streaks were of a white colour, having a slightly blueish tint (probably caused by the mass of intervening air), and their form, to within 15 of the point of convergence, was perfectly straight. The radial point was shown by an irregular mass of auroral light, those to the south being much shorter than the streaks to the from which bright streaks were spread out in every direction, north or west. The appearance of the sky at the time was that of the outstretched wing of an enormous bird. At 9h. 22m. a rich crimson glare was visible in the S. W., dividing the constellations Pegasus and Cygnus, and at 9h. 25m. a resplendent beam of white light 2° in width was conspicuous in the N. E.; its length was about 50, and it was nearly parallel in direction with a line joining the stars a Capella and ǹ Aurigæ, but 3° to the left of them. It remained visible for 5m.

At 9h. 25m. 30s. a white luminous meteor (apparently one of the "Leonides") shot swiftly across the constellation Pisces, having a brightness Sirius, duration o'5sec., and length of path 10°, left no train or sparks.

Iom.

=

At 9h. 32m. the constellation Perseus was overspread by a luminous glare of a reddish colour (known to dyers by the appellation of "ruddy brown,") and which did not disappear for about At 9h. 34m. the crimson glow reappeared in the S.W. between Cygnus and Pegasus, thereby completing a gorgeous arch about 15 in width, extending from the S. W. to the N. E. horizon, passing over the constellations Cygnus, Lacerta, Perseus, Auriga, and Orion. This crimson belt divided the sky into two halves, that on the north being full of auroral streaks, two columns of which were very conspicuous in the north, pass

At 9.30 the western extremity of the arch was of a bright red colour, whilst only a slight appearance of redness was visible in

the E.

The aurora then became wonderfully brilliant, and the rapidity of the changes surpassed anything that had been seen here for years. Flashes of light were succeeded by waves, and these in their turn by small detached clouds, which travelled rapidly across the sky. At 9.45 the waves and streamers seemed to converge to a point slightly S. E. of B Andromeda.

In the square of Pegasus a curiously-formed cloud, in the shape of an enormous bird, suddenly appeared and disappeared several times, sending forth each time streams of light E. and W., as if from its outstretched wings.

At 10 the auroral light was strongest, and then the waves, moving rapidly from the N., appeared to return for a short distance on their path when they had passed a few degrees S. of the zenith, like waves breaking on the sea shore.

At 10.30 two distinct arches of light, the upper one passing through 8 Andromeda, the lower one near Polaris, intersected each other E. and W. at an altitude of about 20°.

At 10.40 all colour had disappeared in the west, but a very brilliant red streamer stretched from the E. nearly to the Twins. About this time a thick cloud of elliptic shape was formed between the points N. W. by N. and W. Beneath this cloud was a pale auroral glare, and from its upper side a mass of broad dark streamers rose towards Polaris. At the E. end of the cloud a very broad streamer moved gradually westward, and shortly afterwards a similar streamer formed near the W. and moved in the same direction.

dark cloud lying horizontally across them divided them into two parts, each of which was distinctly visible.

At 9h. 40m. the streaks had entirely disappeared, being replaced by a diffused auroral glare, similar in appearance to the sky before dawn; but at 10h. the streamers reappeared with equal brilliancy. The radial point had now moved to 2° below B Andromeda, and was now clearly pointed out by an irregular curve, or hook, about 4 or 5 in diameter, which, although observed at different times during the evening, was never completely formed, as 90° or 120 were always wanting to form a complete circle.

At Ioh. 23m. a curious phenomenon presented itself. A small irregular patch of crimson light, about twice the diameter of the moon, appeared over 8 Triangulii, which slowly, and gradually expanded, but after a lapse of about 30s. (when about 15° in diameter), its colour changed to the ordinary bluish white of the aurora, the phenomenon lasting altogether about 2m. Ioh. 25m. a broad greenish white band appeared in the N. E.

At

By this time the centre of convergence had reached ẞ Triangulii, thus showing apparent progressive motion towards the cast at the rate of about 15° per hour (which is the rate of the rotation of the earth upon its axis). It is worthy of notice that in the auroral displays of October 1870 the same stars formed the radiant, and its motion was in the same direction.

At 10h. 37m. a beautiful crimson beam appeared in Auriga (in the same position previously occupied by the white streak at 9h 35m.) Its length was about 40°, and at 10h. 50m, a gorgeous triple streak was visible in the same position, which presented the appearance of a broad crimson ribbon, with a border of white on each side. In about five minutes it faded out of sight.

At 11 o'clock the auroral light was again diffused over the whole northern sky, bounded on the south by a bright milky

arch extending from the E. to the S. W. by S. horizon, visible for ten minutes.

At 11h. 30m. only a few faint streamers, and at 12 o'clock the arch was again visible to the S. E., but aurora very faint.

During the progress of the display the peculiar undulatory phases noticed last year were particularly observed. The waves of light seemed to chase each other in rapid succession along the radiating streaks, coming into collision at the point of convergence. The semicircular masses surrounding this point appearing as if they occupied a fixed position in the sky, and becoming visible to the eye only as the intermittent waves reached them, somewhat analogous to the waves of the ocean dashing against a rock and breaking over it in a mass of white foam.

In conclusion may I venture to suggest the application of photography to auroral phenomena; and perhaps some of your readers might practically answer the query, "Can a photograph be taken of an auroral display?"

342, Argyle Street, Glasgow, Nov. 11

ROBERT MCCLURE

THERE was a brilliant display of Aurora Borealis here on the evenings of Thursday and Friday, November 9 and 10especially the latter night. Towards 7 o'clock a hazy light began to spread itself over the northern sky, near the horizon, not unlike a brilliant twilight. At 8 P.M. two arches were quite distinct, the upper one being well defined, with its apex passing through the head of Ursa Major. Gradually streamers began to pass from this, and by 9h. 15m. the scene was simply gorgeous. I do not remember ever seeing the streamers so expanded-more like flames, nor possessing such intense whiteness, so much so, that the evening was almost as light as if the moon had been shining. After proceeding from the upper arch, their course was most rapid to the zenith--apparently passing at times behind clouds, then suddenly emerging--where a magnificent whirling motion was formed, which kept changing in true Protean fashion. A grand, though somewhat dingy, red haze next appeared in the west, which gradually ascended towards the zenith, when it disappeared. Meanwhile flashes of light, resembling summer lightning, darted upwards from about 45° from all directions, and not least from the south-the N. W. heavens assuming a muddy green colour. About a quarter-past ten P. M. the aurora gradually diminished, especially the upper arch, and streamers from it. Then the lower arch began to give off streamers, but these were short and of short duration, though of considerable brightness. The display of Friday, if it fell short of those of October 23 and 24, 1870, in point of brilliant colours, surpassed them in some respects-e.g. extent of streamers, and brilliancy of light. Barometer corrected and reduced 29°472: Temperature 32.° THOMAS FAWCETT

Blencowe School, Cumberland

THERE have been two magnificent auroral displays on the nights of the 9th and 10th inst. That on the 9th commenced at 10 o'clock, and continued with little interruption until 12.45; and last night from 9.40 until 12 o'clock. Both displays were in the north and north-west, and at times the streamers reached the zenith, but I did not observe them to pass beyond that point. The colours were varied; at one time of a beautiful crimson, at another a greenish white. Last night's display was the most interesting, but not so brilliant as that of the previous night. The aurora made its first appearance by an undefined redness in the north; it then gradually developed into a crimson, and assumed the shape of a vertical pillar, the upper part tapering to a clearly defined point, within a few degrees of the zenith. It remained in this shape and position for two minutes, and then faded away. At 10.15 there appeared, at about 10 degrees above the horizon, a peculiar lightness, like the edge of a dark horizontal cloud illuminated by the hidden moon, but I could distinctly discern some stars below the illuminated stratum, which proves that the cloud was transparent; the stars could not, however, be seen through the lightness. At 10.40 there were three distinct streamers

shooting up from this light, emanating from separate parts, but all in the north and north-west. They then assumed an easterly movement, the right hand streamer before disappearing being in the north-east. The centre one of these was of a very light colour, approaching a faint or whitish green; the others were crimson. At II o'clock I saw an exceedingly brilliant patch undefined in the north-east; by this time some clouds, stratified horizontally, rose from the northern horizon and passed into the light part of the heavens, which seemed to influence the display by intensifying the streamers, which were shooting up, at this time, to the zenith. At 11.30 I saw six beams start across east and west, of a whitish colour with dark spaces between, and the southern one in the zenith. The northern streamer now disappeared, but the auroral twilight was still visible, although gradually fading, and by 12 o'clock all was darkness. I did not continue my observation beyond this hour, the temperature not being conducive to personal comfort.

I may remark that with the exception of the few clouds which rose last night, both nights were perfectly cloudless, and the milky way shone with uncommon splendour. A portion of this band of stars at one time looked grand, as one mighty streamer ran along its course, some of the largest stars being visible through the intercepting redness.

I hope that some of your correspondents will give particulars nights of the above displays. of any magnetic disturbances which may have occurred on the JOHN JEREMIAH

43, Red Lion Street, Nov. II

P.S.-I have been informed that the white horizontal light mentioned in my communication of the 11th inst. was visible at 7.30 on the night of the 9th, but no streamers were seen until the time stated by me.

On Saturday night, at 7.45, I saw in the north western sky a slight auroral redness, but it did not last more than two minutes. Nov. 13 J. J.

Nov. 10th, 11 P. M.-I have just witnessed a most magnificent display of Aurora. I first saw it at 9. 30. Here is an account of it. The bearings given are magnetic.

9.30 P. M.-On the W. was a deep crimson glow of the richest possible colour, about 50° broad and 60° high. From W.N.W. to N. the sky was filled by a mass of white light, pulsating in long horizontal masses moving upwards. At 9.36 they were moving, not very uniformly, at the rate of 33 waves per minute. From the N. to the E. extended a bright horizontal bend of steady white light, marked with vertical lines and having jagged edges. Suddenly from the centre of it shot up a vertical white streamer 3 or 4 wide; this remained stationary for a few minutes and then gradually faded away.

At 9 38 a fan-shaped mass of white light appeared at N.N.E. At 9.45 a band of white light extending from the horizon to a From the centre of this streamed upwards height of about 20°.

a kind of waving flag of intense red light, about 20° broad and At N.N.E. the fan was gone and a reaching to the zenith. bright horizontal band of white light marked with vertical lines had taken its place. It was almost 40° long and 30° high. At 9.50 there appeared an arch of white light about 10 thick. The centre was about 60° high, white, the ends were on the horizon at E. N. E. and N. W. This vanished and was replaced by a horizontal white band, about 60° long and 10° high, the lower edge being about 20° above the horizon. Out of this presently rose four beautiful white streamers. At 9.52 an intensely bright red light was observed at W. At the N.E. were a few patches of white light. At the N.N.E. appeared about ten vertical white streaks for a minute or so. They were 15° high and filled a horizontal space of about 20°. At 9.53 a rather fine meteorite fell. At the N. W. was a red stream about 30° broad and So high, while at W.S. W. was a mass of red light. At 9.55 the mass of white light at E. N. E. threw out a number of jets of light in shape like the streams of water from the rose of a watering can. At 10 P. M. the arch which had vanished reappeared, reaching from W.N. W. to E. N. E. It glowed with a deep white light, which was motionless, except that at 10.2 I observed two downward waves. At 10.3 a long streamer grew out of it. At 10.5 the right-hand end was tossed up into the form of a haycock. At 10.8 a glow spread upwards from the centre of the arch, and filled the upper part of the sky. At the same time a slight patch of red light reappeared in the W. The sky to the S. was lighted up with the reflection of the white light in the N. The reflected light seemed to have a faint reddish tinge.

By 10. 10 nothing was left except the arch, and between 10.10 and II that also vanished.

The stars could be seen distinctly through the aurora. When the light was at the brightest I could see the figures and hands of a large watch, but could not distinguish the figures one from another. Thermometer 30'5 F.; Barometer 29'69 inches. Pixholme, Dorking, Surrey J. E. H. GORDON

66

Structure of Lepidodendron PROFESSOR DYER has already discovered one of the many new facts with which he has yet to become familiar, and hastens, in a straightforward manner, to acknowledge the circumstance; but I must again remind him that this, along with many other facts, was described in No. 129 of the Proceedings of the Royal Society. Professor Dyer further says: Suppose the transverse septa separating these cells absorbed, as probably eventually they would have been, and the rows of cells become scalariform vessels." But I can assure him, as a question of fact, that these cells do not become so changed; consequently his conclusion that the central cells and the investing vessels are but parts of "one central structure" becomes negatived. The separation of these two structures increases with age instead of diminishing.

The Science and Art Department IN your last number there appears a letter signed "Henry Uhlgren," which, among other interesting statements, contains the following: Referring to Mr. Forster's statement in the House of Commons that there was no foundation for the report that "the Examiners after having made their reports had the papers returned to them, with an instruction to reduce the number of successful candidates, as an intimation had been given by a right hon. gentleman that the amount of the Grant due upon those papers must be reduced 20,000/.." Mr. Uhlgren states: "But previous to that a provincial local secretary, hearing the rumour, wrote to ask the Department if it were true, and received a reply saying it was true, and that instead of the amount being 20,ocol. it was 40,000l. (the Department's letter can be produced.)" Premising that the amount of the whole vote for payments to teachers on results in science (which was to be reduced by 40,000/.) was 26,000l., may I ask for the production or publication of this extraordinary official letter?

ECONOMICAL ALIMENTATION

X

IN N glancing over the recent issues of the Comptes Rendus, one cannot but fail to be struck with the practical importance of many of the communications contained therein, a large proportion of which bear special reference to the Siege of Paris. In nearly every branch of science there is some endeavour made to supplement and improve our knowledge in matters such as were then of the greatest importance, and the members of the Académie have come forward eagerly to aid, by advice and precept, in overcoming the misery of a prolonged siege. Unfortunately, but little could be done, even by such men as Fremy, Dumas, Chevreul, and others, against the insuperable difficulties which presented themselves; but nevertheless Paris owes much to her men of science who contributed many services of value, at a time when these were most needed. The manufacture and employment of nitro-glycerine in mines and shells, were successfully accomplished at a crisis when the stock of gunpowder was running terribly short, and the supply of some other reliable explosive was rendered imperative. Hitherto nitro-glycerine had been regarded as a most dangerous combustible, liable to explode at the slightest concussion, and yet we hear of its employment in shells against the Prussians, thundered forth from guns of the

heaviest calibre, without one single instance of its premature explosion being recorded. Again the question of ballooning, although not perhaps very far advanced by the deliberations of the Académie, has, at any rate, been more satisfactorily solved than at any previous period, and Paris has been certainly the first to employ these frail and romantic contrivances in a practical every-day manner, and thus to render the words, “par ballon monté” familiar to the ear as a household phrase. In matters of surgery, as in those of a sanitary nature, sound advice was not wanting, and even the abstract calling of the soldier, -the philosophy of his manner of fighting-formed the theme of much scientific discussion.

But the most interesting, perhaps, of all the subjects with which the Académie des Sciences busied itself, was that of seeking an economical means of alimeniation for the inhabitants of Paris during the siege. Given certain limited sources of supply, a fixed amount of suitable organic matter, and the problem was how to use the same to the fullest and most profitable degree. Of sheep and oxen there was but an exceedingly limited provision in proportion to the very populous state of the city, and although corn and wine were said to be in abundance, there is no doubt the authorities were from the first sorely troubled by the vague estimates that were published of these comestibles.

As a suitable manner of economising corn, M. Gauldrée called attention to the method in vogue among the Romans of parching and bruising the grains, which in this state may be made to yield an excellent and highly nutritious soup or porridge. The corn is carefully sifted by hand, browned without charring, until it breaks when taken between the teeth, and then ground in any available mill ; it is mixed with cold water, boiled for thirty minutes, and seasoned as desired. So economical was this preparation, that at the public kitchens, established in certain quarters of Paris, it was possible to dispense one portion of bouillie romaine together with a small modicum of wine for the amount of five centimes.

A proposition to manufacture artificial milk, brought forward by M. Gaudin, seems worthy of some notice. That gentleman estimated that 500,000 litres per day of milk could be prepared in Paris at an exceedingly trifling cost, which should have all the nutritious qualities of good milk, and which should, besides, be neither unpleasant of taste or smell. An emulsion at a very high temperature is made of bouillon de viande prepared from bones, fat, and gelatine, and when cold, a product is obtained resembling in taste stale milk of a cheesy flavour; the components of ordinary milk are all present, the gelatine representing the casein; fat, the butter; and sugar, the sugar of milk. For admixture with coffee, chocolate, soup, &c., the milk is said to be by no means disagreeable.

Many propositions were brought forward to economise the blood from the abattoir, the plan suggested by M. Gaultier of mixing it with flour in the manufacture of bread being perhaps the best and simplest, as the fibrine and albumen, so rich in nitrogen-of which the alimentary properties are well known-are in this way utilised to the highest degree. Less inviting is the proposal of M. Fud to consume he carcases of animals that died of typhus, rhinderpest, and other diseases, the flesh in these instances being, so asserts M. Fud, capable of use as food, if only cooked in a suitable manner.

More important, however, than all, is M. Fremy's attempt to bring forward osseine as an article of food. Osseine is essentially different from gelatine, which has recently been asserted by chemists-erroneously, so M: Fremy thinks-to be not only unnutritious, but positively injurious to the human system. Leaving, however, the question of gelatine on one side, M. Fremy proceeds to advance the qualifications of osseine as an alimentary substance. Although gelatine and osseine are isomeric, in the same way as starch and dextrine are isomeric, they