whole face of this department of entomological science has undergone a wonderful change in the last twenty

years.

Under these circumstances many an entomologist has no doubt often wished that a new "Genera of Diurnal Lepidoptera" would make its appearance; but such works are not to be lightly undertaken, and it may be long before we can hope to see a good, general, systematic treatise upon this group of insects. In the meanwhile we welcome Mr. Kirby's catalogue as a most important aid to the study of the Diurnal Lepidoptera. It is a complete catalogue of the described species of the group, amounting, as an estimate, to about 9,600 in number, and gives the synonyms both of the genera and species in a clear and easilyintelligible form. With the assistance thus offered to him by Mr. Kirby, the entomologist may easily ascertain what has been done by former writers in this department of his science, and it will be his own fault if he does not keep himself au courant with its future progress.

Criticism upon a work of this nature would be out of place here, and we can only cordially recommend the results of Mr. Kirby's most conscientious labours to the attention of all entomologists.

A Class-book of Inorganic Chemistry, with Tables of Chemical Analysis, and Directions for their Use. By D. Morris. B.A. (London: G. Phillip and Son, pp. 157.) THIS work has been compiled for the use of students preparing for the Oxford and Cambridge Middle Class Examinations, and the Matriculation Examination of the University of London; it lays claim to no originality of treatment, and professes to be simply a collection of "" enlarged notes," "originally culled from the best modern books." Under these circumstances we are somewhat surprised that the author should have ventured to publish it; we are quite unable to detect any special merit in the book, and it is disfigured by many passages which show great want of exactness. Thus, we find 66 nitric acid, or nitric anhydride, N,O,;" "sulphate of potassium or dipotassic sulphate;" the formula of phosphate of calcium is written 3Ca2PO4, of chloride of lime CaOCI,O. We are told that "ammonium and sodium are distinguished by the smell of ammonia on the addition of caustic potash." "Pure water has no action upon the metal (lead), but water charged with air corrodes it, and the oxide of lead thus formed dissolves in the water." Among the redeeming qualities of the book may be mentioned the questions which are selected from various University examination papers, and the examples given worked out in the text; but with errors of the nature of those given above it is impossible to recommend the book to the student, or to regard it as a reliable source of information.

The Elements of Plane Geometry for the Use of Schools and Colleges. By Richard P. Wright, Teacher of Mathematics in University College School, London, formerly of Queenwood College, Hampshire. With a Preface by T. Archer Hirst, F.R.S., &c., late Professor of Mathematics in University College, London. Second Edition. (Longmans, 1871.)

THIS work would have been more correctly described as being "by Eugène Rouché and Ch. de Comberousse, translated and edited by Richard P. Wright," &c. But although Mr Wright can lay small claim to originality, he has shown judgment in the selection of an eminently logical and masterly treatise on geometry, and he has rendered it into clear and forcible English. The arrangement is excellent, and many of the conclusions for which Euclid found it necessary to reason geometrically on each particular case are treated generally by purely logical considerations. Many of the demonstrations, notably that of the pons asinorum, are far more simple and con

vincing than those in Euclid. The difficulty of the twelfth axiom is met by the easy axiom that through a point without a line only one parallel can be drawn to that line. In some points there seems to be an unnecessary alteration of the language of Euclid, as in the definition of a figure, "Surfaces and Lines or combinations of them." This definition seems to have been introduced to enable the authors to describe a locus as a figure; but it having been pointed out that a locus is not a figure, Mr. Wright has described it as a line, but has not restored the word figure to its ordinary acceptation. At the same time it is not quite correct to define a locus as a line, excluding such loci as a pair of parallel lines, the circumference of a circle with its centre, &c. Again, the word circumference is substituted for the word circle whenever the circumference only is intended. It is true that the word circle in Euclid is used in two different senses, but this leads to no ambiguity of ideas; while the use of the word circumference for the circumference of a circle only excludes its application to an ellipse or other closed curve. The word angle is not defined when first introduced, but we are told afterwards that it "may be regarded as the quantity of turning of a definite character around the vertex, which a movable line must receive in passing from the direction of one side to that of the other." We fail to see the force of the words "of a definite character," and would suggest the following definition: "When a straight line moves about a fixed point in itself so as to occupy a new position, the quantity of turning it has undergone is called the angle between the two positions." The exercises are ingenious and instructive, but those of the earlier chapters are much too difficult for mere beginners. The treatment of proportion is good, and the work as a whole is an admirable introduction to the higher mathematics, and a great help to independent investigation. We especially recommend it to students who have found themselves discouraged by the cumbrous form and initial difficulties of Euclid. The second edition contains the alterations suggested by a late eminent mathematician in the Athenæum on the appearance of the first edition, with the addition of the substance of the second book of Euclid, and in a few cases the demonstrations of Euclid have

been restored.

H. A. N.

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 Feb. 4th

AFTER a rather long absence of auroral displays, a brilliant and many coloured example was seen here last night, February 4, not quite so vivid as that of October 1870, but coming next to it so far as my own experience gos.

At about 8 P. M., when the maximum development was reached, all the heavens were more or less covered with pink ascending streamers, except towards the north, which was characteris ically dark and grey, first by means of a long low arch of blackness transparent to large stars, and then by the streamers which shot up from that and along its whole length, for they were green or grey only for several degre-s of their height, and only became pink as they neared the zenith, the region where the more precise phenomena occurred, as thus :

1. The focus of the vertical streamers coming up from all azimuths was very constant among the stars, but was not in the zenith itself, being nearly 18° south and 5° east thereof.

2. The red streamers varied from orange to rose-pink, redrose, and damask-rose, or from strontium a, through calcium a, lithium a, and on to and beyond potassium a, that is, they did reds amongst them; and I, having a very good referring specso to the naked eye, but the spectroscope knew no variety of trum in the lower part of the field of view, giving potassium a, lithium a, sodium a, citron acetylene and green acetylene, be

sides the blue and violet, saw Angström's green aurora line perpetually over citron acetylene at W.L. 5579, and the red aurora line between sodium a and lithium a, but nearer to the latter, say at W. L. 6350.

3. Now, W.L. 6350 in the solar spectrum is a pretty bright scarlet red, so that orange could easily be made of it by the green aurora mixing therewith, and the spectroscope separates each of the two kinds of light with perfect ease But how came potassium red or W. L. 7700, i.e., the blood red, lurid red, and tragedy red of painters to appear so markedly to the naked eye, and yet not be seen at all in the spectroscope, either as a new ingredient or an altered place of the red line? It would apparently be by the mixing up of rays and streamers of the blackness out of that long, low dark arch on the northern horizon. But when a spectroscope fails (as fail it must) to show a characteristic line for a region of blackness, what other instrument can we take to prove the case? Excessively faint greenish and bluish lines appeared at wave lengths 5300, 5100 and 4900 nearly; but the main light in the spectroscope was to the extent of 8-tenths of the whole, that of the green line 5579, and of 17-tenths the red line 6350; while to the naked eye the splendour of the display and its variety consisted in triple mixtures of 5579, 6350, and the unknown dark medium. Could something be ascertained about that, if those who have good telescopic star spectroscopes were to observe a star when shining through one of these inky black arches ?

At 9.30 P. M. when all the aurora had faded or passed away towards the south, where a few straggling pink patches still appeared, the northern horizon and its sky being now free from the black arch, as well as the green streamers, perfectly astonished me by the clear pellucid blue of a true starlight night-sky in a bright climate and clear atmosphere. Evidently the dark arch and streamers are as much a part of the aurora as the green and red lights, but how to investigate them-that is the question. C. PIAZZI SMYTH

15, Royal Terrace, Edinburgh, Feb. 5

LAST evening an aurora of rather unusual brilliancy was seen here. I happened to be out with a friend in the country about sunset, when the sky was completely overcast and fine rain was falling. We noticed that darkness did not come on so quick as usual, and at 7 o'clock it was so light as to lead my friend to believe that the moon was shining above the clouds. Later in the evening slight breaks began to appear in the clouds, through which the first magnitude stars were just visible, and through these openings an intense red illumination appeared. The spectroscope gave from every part of the heavens a very bright line in the green, and another fainter one nearer the blue, together with a diffused light over the green and blue parts of the spectrum. The brightest part of the aurora was towards the S.W. From the large amount of light, although it was raining at the time, it must have been one of the brightest auroras that have been witnessed for years. G. M. SEABROKE

Rugby, Feb. 5

COMING up the Channel on Sunday night last in the P. and O. screw-steamer Delta, about 9.40 P. M., I saw a very fine aurora. The sky was cloudy, which somewhat dimmed its brightness, but it was rather brilliant towards the N.

Having a Hoffman's direct vision spectroscope with me, I turned it towards the brightest red portion which lay towards the N. E., and with a moderate slit got a very sharp and distinct line in the green at or near the position of F in the solar spectrum. No other lines were vi-ible. But on removing the telescope, and observing the spectrum with the naked eye, a fine crimson line revealed itself near C; the colour of it was exactly that of hydrogen a, as seen in a vacuum tube.

I also thought that there were faint traces of structure visible in the blue and violet, but of this I cannot be sure.

There had been traces of auroral phenomena visible early in the same evening. The green line was so distinct that unpractised observers saw it easily. The red line, however, was much fainter, and appeared to flicker.

I much regret that I had no means of recording the position R. J. FRISWELL

of the lines.

ABOUT six o'clock on Sunday evening the ruddy appearance of the upper clouds gave warning of an aurora in prospect, but I was not prepared for the magnificent sight which appeared on

looking out an hour later. The higher part of the sky seemed covered with bright rose-coloured clouds, which, from the dark masses of clouds passing underneath, seemed continually to be shifting in position. Intervals of deep green appeared amongst the red, and these, when looked at with a spectroscope, gave a stronger light than their surroundings. Objects near were illuminated as if the moon had risen behind the clouds. I had a miniature spectroscope of Browning's, with which I examined the brightest parts, and obtained four lines-one very bright green, two very faint nebulous green bands, and one red line. Having a spirit lamp handy, in which were remnants of sodium, lithium, and sulphate of copper, I was able roughly to estimate the positions of the lines. The red was about a third from D towards the lithium line; the very bright green about a third from D to the copper line near b, the other faint green bands were more refrangible, and I should think their places were between 6 and F, and near F, but I could not get their positions so well as the other two; certainly the most refrangible was not so far as the violetpotassium line which I could see in the field.

The light green was present everywhere, the red only showed occasionally with very varying intensity, and the most refrangible green line was also continually varying, but it was brighter than the second green line.

The light around attained its maximum about a quarter to eight, and then very slowly diminished to about midnight, when it had nearly disappeared. A light drizzling rain was falling the whole time. J. P. MACLEAR

Shanklin, Feb. 5

THERE has been a magnificent red aurora here this evening. I saw it first before twilight had quite disappeared, and at first thought it was the crimson of sunset unusually late. It was at its finest between six and seven; at that time there were columns of light shooting up from the horizon almost to the zenith, and Occupying almost half the horizon from the E. of N. round by E. The crimson colour was variegated with bluish white in a way that I have not seen before. The barometer was at about 29.45 inches, with a strong breeze from the south. JOSEPH JOHN MURPHY Old Forge, Dunmurry, Co. Antrim, Feb. 4

THERE was a fine display of aurora here yesterday evening. I first observed it about 5. 30, just in the twilight, but it was then confused with the rays of the setting sun; as the darkness deepened the aurora came out alone, and was then extremely beautiful. It extended from the extreme N. E. to the extreme N. W., but from the reflection of the numerous clouds, appeared to have a much larger area. It was of a bright crimson colour, with the rays golden or orange, of which, however, only a very few were visible.

As the evening came on, about 8 o, the clouds gradually became thicker, and at last almost entirely covered the sky; the only effect then apparent was a deep red glow, which continued with unequal intensity until 11.45, and with all probability much later. At 9.35 there was a break in the clouds towards the E., when the aurora shone forth in all its splendour. The aurora was most certainly visible in daylight, just appearing as the twilight came on.

I have no doubt if the atmosphere had been clearer, we should have had a most magnificent display; as it was, the effect was really beautiful. J. S. H.

Gloucester, Feb. 5

THERE has been a magnificent and extensive auroral display this evening, of which I beg to send you the following account. After a very heavy fall of rain, which lasted in this part of the country from I o'clock P.M. until 5.30 o'clock, there were collected in the northern horizon numerous cirro-stratus clouds, which gradually at first, and afterwards rapidly, moved towards As these were passing the E., with the strata to the S. away, I saw, about midway between these clouds and the zenith a bright patch of pale red light, which became well defined by 6 o'clock. A few minutes after this appeared I saw in the N. W. another patch of red light, and by 6.15 there stretched from N., N. W., and N.E. three very broad streamers converging in the zenith, and forming a splendid crimson canopy, the streamers being quite separated, until meeting, by dark spaces. These slowly disappeared, and of a sudden there appeared a bluish-white streamer stretching N.E. to and passing the zenith by about 10°.

At this time I could see that the Pleiades were partly covered, although not hidden, by a part of this streamer. At 6.35 it faded away. At 6.40 light clouds began to rise in the W. and S. W., and as I recognised this phenomenon as auroral, having seen similar clouds on other occasions of auroral displays, I carefully watched them, and saw at 6.50, in the S. W., a crimsoncoloured patch, undefined in shape, originating from the light clouds. At 6.55 there shot up from the S. beautiful red, crimson, and blue streamers, which converged in the zenith. At 6.58 other bands of crimson and blue arose due S., and joined the others in the zenith. At 7.0 I was quite astonished to see the aurora appear in the S. S. E., by which time the previous brilliant display in the S. had dimmed, and the whole of them formed a southern canopy. During this southern display, the northern parts were quite dark, with heavy looking clouds; but at 7.5 the clouds slightly broke up, and I saw a faint redness in the N.E., about 45° above the horizon. By this time the southern streamers and patches began to spread and assume a mottled appearance, which reached by 7.10 the N. W. At 7.15 the N. W. and E. were quite dark and cloudy, and there remained only slight traces of the aurora in the S. W. high up in the heavens, and by 8.35 it had entirely disappeared. JOHN JEREMIAH

Park, Tottenham, Feb. 4

DOUBTLESS many of your readers witnessed the magnificent aurora which occurred on Sunday, February 4. If any one else has noted the position of the radiant point, as seen from this station, the following observations, made somewhat roughly, from this place (lat. 53° 17' 8" N., long. 6° 10' 22" W., nearly) may be of use in determining approximately the height of that point above the earth.

At 7.15 (Greenwich time) its zenith distance was 23°; its bearing in azimuth 4 E. of S. At 7.30 its zenith distance was the same; its azimuth 15° E. of S. At 9.10 its zenith distance was 13°; its azimuth 1° W. of S. M. H. CLOSE Newton Park, Blackrock, Dublin, Feb. 5

LAST evening (Sunday, Feb. 4) there was a brilliant display of aurora visible in North Devon with some unusual features. At 6 o'clock the sky was clear, except a cloud of deep rose aurora over Orion, and another detached portion toward the west. This soon developed into a cloudy arch of the same colour stretching from east to west; then, a little south of the zenith between the Pleiades and Aldebaran, this arch culminated to an obtuse point of white cloud, something like a broad gothic arch. The northern half of the heavens was quite clear, but a series of radiations towards the south, and spreading east and west, issued from this point. For some time it seemed doubtful whether it was aurora, or a peculiar appearance of the clouds caused by high air currents, and a refraction of light from the sun's rays in the higher regions of the atmosphere. At one time there was some appearance of spiral radiations, or drift of cloud from this point near the zenith, with a distinct but irregular gap of clear sky, somewhat similar to the Coalhole in the galaxy near the Southern Cross; but this did not last long, although the general appearance was continued for more than half an hour, with varying play of light, over a space of about 140° of the southern heavens, with pretty well-defined eastern and western boundaries of deep rose colour, culminating in the white focus near the Pleiades, which appeared the centre of action. rose colour was chiefly confined to the eastern and western boundaries, with intermitting starts of whitish radiation toward the south. Occasionally well-defined streaks of a lighter tint crossed the western portion of the rosy cloud, which appeared to originate from the light of the sun, now, of course, far below the horizon. At length the eastern portion became less brilliant, but still Orion was enveloped in a steady rosy haze, although it gradually became fainter, until, a little before 7 o'clock, the rosy colour below Orion toward the eastern horizon became as brilliant as ever, and soon a straight broad ray of rose colour started up from the horizon. This was not curved or arched, like the whiter radiations which seemed to originate from near the zenith; nor was it, like them, intermittent and wavy; but had the appearance of a broad beam of rosy light originating below the horizon, and darting straight upward in a diagonal direction, proceeding over Castor and Pollux and Jupiter. Then the north side of this became of a peculiar light bluish green; if I may be allowed to coin a word, it was of a moonshiny colour. If the moon had been a few days younger, I should have thought it originated from the

The

moon. This very peculiar and distinct broad beam or bar of light almost developed prismatic colours from its southern rosy edge to its northern bluish-green well defined border. There was also a somewhat indistinct tendency to the same prismatic appearance, spreading some little distance over the heavens on the south side of this beam near the zenith. The northern segment of the sky from Castor and Pollux to about direct west was still perfectly clear, both from cloud and aurora, right down to the horizon; there was a bank of cloud along the southern horizon. About 7 o'clock there was an appearance of rosy tint to the north of the peculiar straight bank spoken of, and this reached as far as the pointers in the Great Bear. About the same time there was a peculiar development of white cloud from the zenith toward the north-west, streaked and fringed with well defined radiations, and this gradually increased until the northern portion of the heavens, which had hitherto been quite clear, was covered to within 30° of the horizon, the border of this cloud being very distinctly and deeply serrated with fan-like shapes radiating from near the zenith. The phenomena I have described occupied more than an hour, and my attention was now drawn from it until after 8 o'clock, when the whole heavens were cloudy, but behind and between the clouds the rosy tint was still visible as an irregular arch stretching from north to west. As the clouds broke off the whitish wavy radiation could be occasionally seen still issuing from near the zenith, and across the western part of the rosy arch were occasionally seen the straight diagonal bars of a brighter shade, apparently caused by the light of the sun, but the clouds obscured most of the phenomena. At a last look near 9 o'clock the clouds had somewhat cleared, and there were two brilliant arches, more like the regular aurora from the northwest horizon towards the zenith, at right angles to the more cloudy arch, which had been visible for some time stretching from the north to the west. W. SYMONS Barnstaple, Feb. 5

LAST evening (Sunday, February 4) the sky presented a weird and unusual aspect which at once struck the eye. A lurid tinge upon the clouds which hung around suggested the reflection of a distant fire, while scattered among these torn and broken masses of vapour having a white and phosphorescent appearance, and quickly altering and changing their forms, reminded me of a similar appearance preceding the great aurora of October 1870. Shortly some of these shining white clouds or vapours partly arranged themselves in columns from east to west, and at the same time appeared the characteristic patches of rosecoloured light which are seen in an auroral display.

About 8 o'clock the clouds had to a certain extent broken away, and the aurora shone out from behind heavy banks of clouds which rested on the western horizon, the north-eastern horizon being free from cloud and shining brightly with red light. And now, at about 8.15, was presented a most beautiful phenomenon. While looking upwards I saw a stellar-shaped mass of white light form in the clear blue sky immediately above my head, not by small clouds collecting, but apparently forming itself in the same way as a cloud forms by condensation in a clear sky on a mountain top, or a crystal shoots out in a transparent liquid, leaving, as I fancied, an almost traceable nucleus or centre with spear-like rays projecting from it; and from this in a few seconds shot forth diverging streamers of golden light, which descending met and mingled with the rosy patches of the aurora hanging about the horizon. The spaces of sky between the streamers were of a deep purple (the effect of contrast), and the display, though lasting a few minutes only, was equal if not excelling in beauty, though not in brilliancy, the grand display in 1870, before alluded to, in which latter case, however, the converging rays met in a ring or disc of white light of considerable size.

What struck me particularly was the aurora developing itself as from a centre in the clear sky, and the diverging streamers apparently shooting downwards, whereas in the ordinary way the streamers are seen to shoot up from the horizon and converge overhead. The effect may have been an illusion, but if so it was a very remarkable one. Examined with one of Mr. Browning's direct seven-prism spectroscopes, I saw the principal bright line in the green everywhere (the other lines were not visible), and noticed the peculiar flickering in that line which I noticed in 1870, and which has also I think been remarked by Sir John Herschel. The general aurora lasted for some time till lost in a clouded sky, and in fact rain was descending at one time while the aurora was quite bright. Strong wind prevailed during the

night. The aurora was probably extensive, as the evening, notwithstanding the clouds, was nearly as bright as moonlight. Guildford, Feb. 5 T. RAND CAPRON

The Floods

Two of the largest districts which are most constantly flooded are, perhaps, Oxford and "The Plain of York." The same cause floods both these districts, namely, what Mr. Mackintosh has called "Colonel Greenwood's hard gorge and soft valley theory." Both these districts have been worn down by rain and rivers in the soft oolitic strata; and the Humber and the Thames have ever had, and have now, to force outlets through comparatively hard chalk gorges. The rain-flood waters, checked at these gorges, overflows and deposits alluvium behind the gorges. The same takes place in the soft strata of the Weald, behind the nine comparatively hard chalk gorges of the North and South Downs. GEORGE GREENWOOD

Brookwood Park, Alresford, Feb. 3

Zodiacal Light

THE evening of Feb. 2 being clear, after a long persistence of rainy cloud for many days, about 6.5 P.M.I began to notice the existence of a zodiacal light. Some time later, probably about 6.40, it was considerably brighter than any portion of the galaxy in sight at the time, though this might not have been the impression of an inattentive spectator, as the gradual melting away of its edges produced much less contrast with the ground of the sky than the better defined outline of the Milky Way. Its light was, in fact, so imperceptibly diffused that it was impossible to fix its boundaries or extent with any accuracy. Its general position was, however, undoubtedly a little below the square of Pegasus (where its upper edge fell short of a and 7), and beneath the three stars of Aries; but its light was here so enfeebled that its termination was quite uncertain, and it could only be said that the direction of its axis was towards the Pleiades. Its breadth where most brilliant, near Pegasus, might probably be estimated at 8° or 9°, from comparison with the distance from a to 8, and with the length of the belt of Orion; but this determination was liable to great uncertainty. It was thought to show a ruddy tinge, not unlike the commencement of a crimson Aurora Borealis; this may have been a deception, but it was certainly redder or yellower than the galaxy. At 7 I examined it with a little pocket spectroscope, which shows very distinctly the greenish band of the aurora; but nothing of the kind was visible, nor could anything be traced beyond a slight increase of general light, which, in closing the slit, was extinguished long before the auroral band would have become imperceptible. still visible at 8.30. The phenomenon had been previously noticed, but with less distinctness, on Dec. 30 and Jan. 11. T. W. WEBB Hardwick Vicarage, Herefordshire

It was

Magnetic Disturbance during Solar Eclipse WITH the known relation existing between the sun and terrestrial magnetic disturbance, it is not surprising that some indication of a change in the earth's magnetism might be expected during a solar eclipse; and the case cited by the Rev. S. J. Perry, of its supposed observation by M. Lion, is not the first instance of the kind.

Shortly after the eclipse of 1870, Signor Diamilla Müller, of Florence, published a paper in the Gazzetta Ufficiale, No. 17, describing some magnetic observations made in Italy during the 21st, 22nd, and 23rd December, and from which it appeared that there was a slight variation in the curve of the 22nd, at the time of the eclipse, which did not appear in the curves of the preceding and subsequent days. Signor Müller at once concluded that the variation was produced by the eclipse; but it was pointed out by Senhor Capello, of the Lisbon Observatory, that the same disturbance was recorded by his self-recording instruments, but it occurred there some time before the totality. It was also recorded by the instruments here, and proved to be insignificant when compared with other disturbances continually observed.

A careful examination of the curves for the time of the 1860 eclipse has also failed to show any trace of a similar movement then occurring. G. MATHUS WHIPPLE

Kew Observatory, Feb 5

Circumpolar Lands

MR. HAMILTON, in NATURE of January 25, refers to a paper in which "the rising of the land at the poles is inferred as a ne. cessary result of the cooling and contracting of the earth." He then goes on to give the substance of part of the paper, beginning as follows:

"If a spheroid of equilibrium, in motion about an axis, contract uniformly in the direction of lines perpendicular to its surface, a new spheroid is produced, having a greater degree of eccentricity, because if equal portions are taken off the two diameters, the ratio of the equatorial diameter is increased. This is equivalent to a heaping up of matter around the equator."

The reasoning of this latter passage appears sound, but it con tradicts the former one. As I have shown in my letter to which Mr. Hamilton replies, the facts, so far as known, appear to point to a relative increase of the polar diameter; he admits this, and then gives reasons for expecting a relative increase of the equatorial one. He must have made some oversight.

Old Forge, Dunmurry, Jan. 27 JOSEPH JOHN MURPHY

THE HISTORY OF PHOTOGRAPHY

TRUST you will kindly allow me space for a few lines on the subject of some rare specimens connected with the History of Photography, now in the possession of Madame Niépce de St. Victor, whose husband it will be remembered was the first to employ glass, and a transparent medium (albumen) for the purposes of photography, thus discovering, to a great extent, the process of Photography as it exists at the present day. The first glass negative, or rather cliché, Madame Nièpce possesses, as likewise prints executed in 1848.

Niépce de St. Victor was likewise one of those who have worked hard to secure natural colours in the camera, some very perfect specimens-photographs of coloured dolls-which prove distinctly that the solution of the problem is not impossible, as many believe, are also included in the Niépce collection, together with some results of early photo-engraving.

Madame Niépce and family have been left, I regret to say, in very straitened circumstances, for the busy philosopher in his lifetime had but the pay of a subordinate officer in the French Army to subsist on. She has placed in the possession of the Photographic Society this valuable collection of her late husband, and it is proposed to exhibit it at the next meeting of the Society on the 13th inst., and any institution or individual desiring to become possessed of some of the specimens will be readily furnished with information by H. BADEN PRITCHARD

GANOT'S PHYSICS*

GANOT'S Physics is so well known in this country

that our task is very different from that of reviewing

a new work, and we can do little more than compare this edition with the previous. It is unusual for any large scientific work to pass through five editions in about ten years, and the value of the book may be estimated by this fact. It has passed through more than twice the above number of editions in France, and has been translated into various European languages. In the present edition the type has been altered, and the size of the page somewhat increased, while twenty-eight new illustrations have been added, and the text has been augmented.

The doctrine of energy has of late been so largely developed that we are surprised to find so small an amount of space given to the subject. No more than two pages are devoted to it, while the term "transmutation of energy," does not appear in the index. Neither do we find the terms "Kinetics" and "Kinematics;" yet we imagine that the student who presented himself as a candidate for a Science Scholarship at any of our Uni

* An Elementary Treatise on Physics, Experimental and Applied. Translated and Edited from Ganot's "Eléments de Physique," by E. Atkinson, Ph.D., F.C S. Fifth Edition, Revised and Enlarged. 828 pp. 8vo. (Lon don: Longmans and Co. 1872.)

versities, not knowing the meaning of these terms, might find himself quite at sea in some of the questions. In

gretted; for just as the philosophy of Francis Bacon used to be called the "New Philosophy," so might the Natural Philosophy developed in the treatise of Tait and Thomson be called the "New Physics." The experimental science of the future must be based, we conceive, upon the system therein elaborated.

We are glad to notice a very good account of Morin's apparatus for demonstrating the laws of falling bodies (p. 49), which does not appear in the 1868 edition. The principle of this, it will be remembered, is to cause a falling body to trace its own path upon a rotating cylinder. The accompanying diagram (Figs. 1, 2) needs no explanation. The vanes are for the purpose of producing uniformity of motion in the revolving cylinder; the falling weight is a mass of iron, P, furnished with a pencil, which presses against the paper on the revolving cylinder. The curve traced can be proved to be a parabola, and the paths

X

n

Y

Ꮓ

FIG. 2.

deed we do not find much introduction of the terms of the Thomsonian Physics, and this is surely to be re

FIG. 3.

FIG. 4.

traversed in the direction of the descent are shown to vary directly as the squares of the lines in the direction of rotation.

Under the head of "Endosmose of Gases" (p. 97) we find no account of the cause of diffusion of gases, the experiments of Graham, the determination of the relative velocity of atoms by Clausius, and the explanation of such facts as the rate of diffusion of hydrogen being four times greater than that of oxygen. But it may be argued that this rather belongs to Chemistry.

We are glad to see that the law which relates to the volume of gases under varying pressures is now called after its true discoverer, "Boyle's Law," but the experiment, demonstrating at once the incompressibility of fluids and the porosity of dense bodies, is, as usual, attributed to the members of the Accademia del Cimento, while it was in reality proved twenty years earlier with