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or o/ tfo oh systems would moyo ten times faster fo^^lowej lon lhan m aphelion, and for ten meteors »леэвош- riven small range close by perihelion

sc^-Ж! to ÓM b°' 100 along an equal range close by

Ьсл ex. ¿ion. For 10,000,000 meteors then close by ne letriheKon there would be 100,000,000 equally • aislóse by aphelion. But the latter set would be I t -?• spread nniformly over the surface of a sphere '! having a diameter ten times greater than that of the sphere over' which the latter set would be spread. The surface of the larger sphere would, therefore, be 100 times greater than that of the smaller sphere, while the number of meteors spread over it would be only ten times as great. It follows that meteors would be spread only onetenth as richly at the aphelion distance as at the perihelion.

On the average, the meteors belonging to such a system as the November one are spread eighteen tunes as richly {cubical space for cubical space) mar the point of their closest approach to the sun as near the orbit of Uranus, beyond which their aphelion lies. Giving to tho August meteors a period of about 100 years (the real period is certainly greater), we get a mean distance of somewhat less than twenty-two (the earth's as one), or an aphelion distance more than forty-three times exceeding the perihelion distance; so that the density with which these meteors are distributed in cubical space is, on the average, more than.forty-three times greater at the point of nearest approach to the sun than at aphelion. And the üke is true, mutatis mutandis, of every eccentric meteoric system, whether traversed by the earth or not.

To sum up then, we have—

1. Absolute certainty that the number of meteoric systems is enormous.

2. Very good reason for believing that meteoric systems aggregate as systems towards the sun's neighbourhood; and

3. Absolnte certainty that individual meteors in every elliptic system are, on the average, mach more thickly spread (cubical space for cubical space) near the perihelia than near the aplielia of their orbits.

The last relation, only true on the average as expressed for any given meteoric system, must be absolutely true when all the meteoric systems are considered together. For example, when the gem of the Novemlier raeteor-гтя—as Mrs. Wood ñnely called its richer portion—is travelling out in space beyond the orbit of Uranus, this system is, for the moment, richer out there than near perihelion, where the poorer pari is passing. But we cannot doubt that this temporary effect is much more than counterbalanced by the superior aggregation of the number* of comitless other meteoric systems near the sun—we cannot, I mean, imagine that any one system, or even several systems, can even temporarily disturb the preponderance of aggregation in the sun's neighbourhood.

Now. even giving up the second of the above conclusions as not absolutely demonstrated, the other two remain, and leave ns no manner of doubt whatever that the neighbourhood of the sun must be more abundantly crowded with meteors than the track through which the earth pursues her course. But it has been proved that within every space along that track equal in size to the earth there must, on the average, be some 13,000 large meteors, and forty times as many small ones. If the whole space enclosed by the earth's orbit (to consider no farther) is at least as richly supplied with meteors as this (and I see no escape from the conclusion), some rather remarkable results follow, which we shall do well to consider somewhat attentively.

Ц ÎÇ -i ]e

Here is one :—Let Eibe a cylinder enclosing the earth at E. passing pretty close by tho snn S at N,^ and extending to the earth's orbit again at e. The length of this cylinder would be about 180,000,000 miles, a length containing the earth's diameter some 22,800 times, and therefore the volume of the cylinder would exceed the earth's more than 34,000 times. The cylinderwould therefore contain more than 442,000,000 meteors such as become visiblo to the naked eye when traversing our atmosphere, and 17,680,000,000 smaller ones, or more than 18,000,000,000 meteors of one sort or another. These would be illuminated by the sun with more or less brightness—those near N with an inconceivable glory of light (these, too, would be so heated as to be inoandescent, if not vapourised), and they would turn more or less ol their illuminated portions towards the earth.

Is it conceivable that so tremendous an array of illuminated bodies, lot them be as minute as we can suppose them to be, would give no appreciable light when the sun is totally eclipsed? Is it an idea so utterly wild and fanciful that the light actually seen during eclipses—where this long array of illuminated bodies has been shown to be—the sun's corona, I mean,—does actually come from them? Or, if we were disposed still to be doubtful as to this interpretation, ought not all doubt to be removed when such a practised observer as Captain Noble tells us he has actually seen Venue (when placed somewhat as shown in the figure at V) projected as a black body on a relatively light background? When some one shall have shown me whence the light illuminating that background can have come, except from beyond Venus, or how, supposing it so to come, any doubt can exist that during total eclipse we ought to see some euch light, I shall prepare to admij; that there is no objection to Mr. Lockyer's theory that the corona is a phenomena of our own atmosgbwe, except "that it does not square with Mr. Prooior's opinions."

Bn* Uieve are other consequences to bo considered. I reserve them for a future paper, in which I shall, in the first placo, show how the results here deduced serve to explain the zodiacal light in a very satisfactory manner—even the phenomena hitherto considered [most perplexing; how the zodiacal light is brought into direct association with the corona; and, fnrther, how the peculiarities of comets, as distinguished from meteoric systems, find their counterpart in the peculiarities of the corona and zodiacal light. I would specially invite any readers of the English Mechanic who find my reasoning either obscure or unsound in any phice, to kindly point out their difficulties or objections. I have no wish to make out a case, but to interpret, if I can, the phenomena I have referred to. Let me add that I can see no reason for waiting because we hope to gain new information during the eclipse of next December. The more earnestly we try to educe the meaning of what we have already learned, the more significant will new observations become. There is a good .leal of affectation (to say nothing of downright laziness) in the continually repeated advice to wait for fresh observations. The warning addressed specially to me reminds me of Miss Lavinia Spenlow's remarks about " maturo affection." "Mature science," Professor Pritchard seems to say, "does not easily express itself. Its voice is low. It is modest and retiring; it lies in ambush, waits and waits. Snch is the mature fruit. Sometimes a life glides away and finds it still ripening in the shade.'' I confess I prefer a fruit of somewhat quicker growth.

(To be continued.)

THE WORLD: ITS FORMATION AND ANTIQUITY.

By Akthuk UsDEnim,!..

(Continued from page -111.)

Chapter V.

HAVING investigated tho nature of the igneous rocks, we now come to the consideration of those of an aqueous formation. The oldest, and in consequence the lowest, deposit of this species is that which is called the mctamorphic (from two Greek words, signifying changed in form) or primary class. The rocks of this series are termed metamorphic because they appear to have undergone considerable alterations since their deposition, and under the influence of pressure, heat, and chemical forces, to have assumed a semi-crystalline character, which is not possessed by the ordinary aqueous strata. They are also called non-fossil ¡ferons, hypozoic, ¡under life), or azoic (without life), because they contain no remains of plants or animals.

The primary, metamorphic, non-fossiliferous, hypozoic, or azoic class (for by all these names is it known) comprises three systems or groups— namely tho Gneiss, the Mica Schist, and the Clay Slate systems.

It will, perhaps, be noticed that in the list of rocks in order of superposition I have placed the clay state system in the class of secondary rocks. This was, however, a lajmts calami, which I mnst beg my readers to excuse. It should have stood at the head of the primary class, and the Cambrian system should have been inserted in its place at the bottom of the secondary class. The gneiss is the oldest and lowest of the three,

and I shall therefore proceed to the consideration of it first, and shall then take the others in order. In a previous chapter, I said that, after the first convulsion had taken place, the sea deposited a system composed of the detached particles of granite. This deposition formed the gneiss system, and so well was the character of tho original granite preserved that it is in many eases extremely difficult to tell the difference between the granite and gneiss rocks. The stratification of gneiss, however, is a sure test, and in most cases it is marked enough, although in others, on account of tho very contorted and flexured stratification of the primary rocks, it is a work of difficulty to follow it. Gneiss is, however, of a neater appearance than granite, if I may be allowed to use snch an expression.

The contorted appearance of the metamorphic strata is (when the flexures are large) generally accounted for by the supposition of an immense lateral and vertical pressure acting upon them while yet in a soft and yielding condition; and when the contortions are small, they are explained by the help of an analogous case, which presents itself to our notice at the present day— namely, the phenomenon of ripple marks, which is seen on the sandy beach of any of our many watering-places. The sea at the time of the. deposit of the gneiss was in an excessively troubled condition, and in consequence tho motion of the waves was communicated to the very bottom, instead of being confined, as now, to the shallow portions of the ocean. The first cause of contortion, namely, lateral and vertical pressure, has been experimentally demonstrated by Sir C. Lyell. He took some clay, and having made of it several slabs or cakes, ho placed them one upon another ou a table; ho then placed two pieces of board, one at each end, and upon the top he laid another board very heavily weighted. He then, by means of a press, forcibly contracted the space between the side boards. The result was that the slabs were bent and contorted in a similar way to tho strata of the primary rocks.

The strata of the gneiss system are gneiss proper, composed of quartz, felspar, and mica; syenitic and porphyritic gneiss, oí the same minerals as syenite and porphyry respectively; and quartz rock.

The next system in order of superposition is the mica schist. This has by many geologists been classed with the gneiss, both on account of the similarity of the characteristics of both systems, and also becauso their order of superposition, unlike any other groups, is somewhat uncertain. However, as for purposes of description it is more convenient to keep them apart, I have adopted that method. Mica schist difiera from gneiss in the entire absence of felspar, and has, therefore, anappoarance of a white glistening stone, which is for the most part laminated like slate. It is, as a rule, softer than gneiss, more distinct in its lines of stratification, and less crystalline. Its chief strata are mica schist proper, composed of mica and quartz; fuie schist, in which talc supplants the mica; chlorite schist, where chlorite takes the place of the mica and gives a greenish colour to the stone; hornblend and actynolite schist, of horublcnd and actynolite respectively with quartz; and primary limestone, such as the highly crystalline Carrara, and other pure marbles. The meaning of the word schist is somewhat similar to that of slate, and is used to signify that such rocks are laminated. Tho gneiss and mica schist systems are very plentifully distributed over Scotland, but are extremely rare in England. I may mention, as examples, the passes of Glencoe and Killiecrankio, and the mountains around Loch Katrine.

We now come to the clay slate group, specimens of which are so continually seen in the roofing of our houses. It is of various colours, from light grey to black, and its texture is also subject to considerable modification; it is, however, much finer than that of gneiss or mica schist, and the minerals of which it is composed appear to bo the finer and moro impalpable particles of water than matter. The lamination of this group is particularly marked, and renders it of the greatest use in the arts, as it splits up into plates of the most perfect thickness throughout. The causo of this property is very obscurely understood, but is thought to proceed from chemical and magnetic action combined with heat, acting whilst the strata were under great preseure. The line of lamination, or cleavage, is not generally the same as that of the strata, but lies at all angles to it.

Tho scenery of the clay slate system is very wild and abrupt, the strata being tilted np into the most fantastic shapes and forming precipices of tremendous depth.

I hare now reviewed the primary rocks, and in my next chapter shall commence the consideration of the secondary class, which is of far greater extent and of mnch more interest than the metamorphic or non-fossiliferous systems. ('To be continued.)

MICROSCOPICAL JOTTINGS IN TOWN AND COUNTRY.

No. IV. ППНЕ name of micro fungi is legion, there are

I at least 2,000 species for the study of which the microscope is essential, and, as I have before said, any person having good eyes and a fair amount of patience may collect a goodly number with little difficulty, from the beautiful "cluster cop" (.Ecidium) to the humble smut (Ustilago). He will find ample scope for real earnest work which is not without its reward.

Whilst upon the subject of fungi, I may touch upon the yeast fungus, concerning which enquiries have lately been made by correspondents in the English Mechanic. In John Quekett's "Lectures on Histology," and in Dr. Carpenter's "Microscope and its Revelations," drawings are given of the various stages of the development of this plant, accompanied by a lucid description, which we cannot do better than abridge. The initiatory etage is that of a simple cell, which we may regard аз the perfect plant. Place one of these in a saccharine fluid containing also albuminous matter, and each cell "rapidly puts out one or more projections which appear to be buds," that speedily become new and complete cells, themselves to increase in like manner, so that in a few hours a single cell will develop into several rows of cells, all remaining in continuity with the parent cell, but existing independently, and exercising all the functions of separate plants. If we check the process of fermentation these separate into eingle cells, and return to the isolated state we call yeast. Any of our readers can easily examine these for themselves if they be provided with a good ¿in. or iin. objective, and, by a little ingenuity, can devise means by which the process of development may be watched for a considerable period.

Various " insect preparations " are generally to be found in our microscopical cabinets, and usually attract a considerable amount of attention from the outside public, so that I am not surprised that "C. R. H." (<iy. 4328), requests me to give some information as to the best means of "putting them up." It will perhaps be more interesting to the readers of the English Mechanic generally if I give a few hints as I touch upon different kinds of insect preparations than if I give "C. R. H." a formal reply. Premising that he will require a few glass slips 3in. x lin., afew thin covers, either square or round, about Jin. across, a little balsam and gold size or asphalte varnish, I will for the present dismiss the subject. But if our readers wish a short paper on mounting I will try and meet their wishes as best I can.

The House Fly.—The proboscis is the favourite portion of this insect, and is really, when nicely prepared, a splendid object in the hands of a good manipulator, and furthermore affords a good test of the correctness of the lens used. We have to remove it from the head of the insect, souk it awhile in pure turpentine and mount it in balsam, paying great attention to its arrangement on the slide.

Balsam, when used in mounting, should be of medium thickness, and it is usually desirable to warm both slide and cover slightly, in order that the balsam may flow freely, and air bubbles be less likely to be included. When mounted, the slide must be placed awhile in a warm room, until the balsam becomes hardened, when the slide may be cleaned off. Under a good lin. objective we can make out the anatomy of the proboscis very well. Briefly we may describe it as consisting of the two lobes of the lingula, or the expanded portion which is pressed upon our hands when tho creature "bites" us, of the lancets formed by metamorphosis of the lesser pair of jaws (called the maxillne), and of the maxillary palpi, small appendages attached to the latter. Certain ring-like markings on tho lobes of the lingulre are really metamorphoses trachea, as may be made out by a good lens and careful focussing. I have often watched, with much interest, through an ordinary inch pocket lens, the creature at work upon a lump of sugar, and have seen it pump up

the dissolved sugar as though it were determined to lay in as much as possible in the least possible time.

The eyo of the fly is perhaps not so easily prepared. We must carefully remove it by cutting round it with a fine pair of scissors, lay it on a slip of glass and wash it freely with clean water. A few niiuutes' soaking in potass solution will improve it, but I have rarely found this to be necessary. So soon as we have made the eye perfectly clean by washing away all its pigment, we may remove it to a clean slide and lay a piece of thin glass over it, add a little pressure to ensure its flatness (it is often needful to notch the eye all round), and allow it to dry at its leisure. When quite dry, we may moisten it in balsam. Under a good iin. or Jin. we find that the eye is composed of a great number of hexagonal facets, of which there are as manyas 4,000 in the two eyes. Each facet is the "corneule" of a distinct "ocellus," and may be correctly regarded as a perfect eye. The question has often been asked whether a fly with its 4,000 eyes sees but one object or many at once. To this there can, I think, be but one answer—viz., that it receives but one image at once, and that one impression only is transmitted to its brain. The why and wherefore of this, our readers may profitably work out by the aid of their microscopes. To explain it here would require diagrams and more space than I can ask.

I must reserve further notes on the fly until my next, which I think ought now to be my last, as it is unfair for one contributor to monopolise space for too long a time together.

H. P., Hull.

TELESCOPIC WORK FOR MOONLIGHT
EVENINGS.
Вт W. R. Birt, F.R.A.S.

IT is well known that the finest views of lunar scenery are obtained about the times of the first and last quarters of the moon, when the boundary of light and darkness, which is technically called the terminator, divides the visible disc into two portions; in the first case, before the full, the western or day side, and the eastern or night side, which in the second case, after the full, are reversed. With such telescopes as those mentioned by Webb in his interesting work, " Celestial Objects for Common Telescopes," the irregular and rugged line separating the two is well brought out. On the west of the first lunar meridian (the line on Webb's map joining the letters S and N) may be detected, about the time of first quarter,the formations numbered on the map 288 (Hipparchm), 289 (Albategnim), and 290 (Parrot), and as the terminator moves eastward one of the finest chains of walled plains to be found on the moon, just eastward of the first meridian, comes into view—viz., 208 (Ptolemaus), 207 (Alplutmnui), 204 (ArzacM), 202 (Purbach), 201 (Regiomontanm), and 200 (Waller.) These formations are mentioned as being calculated, when beheld through a good glass, to arrest the attention of the observer by the magnificence of their appearance and the quantity of interesting detail to be found in their iinmediato neighbourhoods; it is, however, to a few of the characteristic foatures of Hipparchm that attention is solicited, as this formation exhibits in many respects, a marked difference from its neighbour Ptolemccm. Although the boundaries of each may be easily recognized when the sun has newly risen upon them,those of Hipparchm differ so greatlyfrom the usual boundaries of walled plains, which are more or less visible under every angle of illumination, as to remove Hipparchm from this class of lunar objects, its general outline being lost to view in about forty-eight hours after sunrise upon it, it is rather, as Beer and Mädler describe it, " an assemblage of diverse lunar forms than a general whole." Under suitable illuminations these diverse forms possess considerable interest for the explorer of the moon's surface.

If the observer be fortunate enough to catch the terminator on the eastern part of Hipparchm, there is little doubt of his being greatly interested in contemplating the high chain of mountains which separates Albategnim from Hipparchm. The summit of this chain, which is папок, appears at the time of sunrise upon it as a brilliant line of light, and he will soon detect upon its western portion three craterlets—the northern half of the middle one having been elevuted apparently by the upheaval of the narrow strip of mountain, while the southern half has remained at a lower level. Schmidt

first noticed this narrow mountain chain perforated in parts by craterlets, and which he calls a crater-rill, on February 3rd, 1805, although the eastern part of the same mountain wall he had known as early as August 17th, 1843.

The observer will not be long in ascertaining, under the oblique illumination at the time of first quarter, or a little biter, that the mountain wall separating A Wategnim from Hipparchm is but a small portion of a line of cliffs extending eastward to the junction of the borders of Ptolenutu» юи\А1р)шн*ш>, a very rugged and rocky region, and westward as far as the two craters on Webb's map 64 (Ritter), and 65 (Sabine). The faces of these cliffs are very steep towards Hipparchue, the depressed level of which appears to have resulted from subsidence. At the time of full moon, a ray from Tycho, the metropolitan crater of the moon, as it is called by Webb, crosses Hipparchm. This ray, by comparing lunar photograms taken at the full, and shortly after the first quarter, is found to traverse very uneven ground, which is sufficiently connected and linear in its direction to warrant the supposition that it has been dislocated and shattered in the line of the ray, and therefore that the ray and fault are mutually connected. At the point where this fault or ray crosses the mountain wall common to Albategnim and Hipparchm, the wall has been greatly disturbed, and from the manner in which this has been effected it is probable that the ray from Tyclu) is the most recent of the two. In Webb's map there are four small craters, three on the S.W. border of Hipparchm, and one within its enclosure north of them. The largest has been called Halley, and the one west of it Hind, the northern one within the enclosure of Hipparchm has been termed Horrox. The observer will find a small crater west of the three, on the S.W. border, forming a conspicuous row of four craters, which is well worth his study. From the three craterlets on the mountain wall between Albategnim and Hipparchm, the cliffs pass close to the N.E. border of Halley. An interesting feature connected with Halley is a peak common to its border and the cliff, which according to Beer and Madler rises to the height oí 3,543 English feet. The western foot of this peak is perceptible within the interior of Halley, and it sends out a spur towards the N.E. on to the floor of Hipparchm, which has a rapid declivity. As the sun rises upon the spur it appears as a fine line of light, and is a very interesting object,

There are similar peaks on many parts of the moon's surface well deserving attention. Of these mention may be made of Pico (Webb, 131) on the south border of the ancient plain called Newtvn bv Schröter. The plain is visible for a short time only, but Pico, with an altitude of nearly 8,000ft., may always be seen. There is also a fine peak on the east border of Plato (Webb, 132) named by the late Dr. Lee "Rapes Smythii," which Schmidt finds to be 9,000ft. high. Peaks of this kind should be well examined under every phase of illumination.

Mention of a feature connected with the mountain wall to which the attention of the observer was first directed must not be omitted; it is that the western of tho three craterlets is the brightest, and immediately below it, on the face of the cliff, is a shallow ravine, which appears on Rutherford's photogram, 1865, March 6th, as if it had been excavated by the flowing or descent of some material over it, and on the ûoor at the bottom of this ravine is a mound of apparently accumulated material. It is very desirable that further observations of craterlet, ravine, and mound, should be made, also that the rocky region in the intermediate neighbourhood should be weU examiued, for it is ш auch localities that discoveries are likely to be made. Schmidt says:—" As other objects of a rigorous and searching examination, I mention those little craters, crater rows, crater rills, thot, situated ш the interior of the ring mountains, form the limits of the plain and the beginning of the wall mountain. Here the eruptive forms have issued, as it were, out of cracks, and in parts of considerable and high mountains, where two mountain masses approaching each other form a narrow valley, or a sharp corner."—Report of the British Association for the Advancement of Science, 1865, p. 307. Craters are much more numerous on the rocky land filling the region between Albategnius and Ptolemaus than they are to the westward, bnt as yet no evidence of recent formations has been met with.

It is probable that on some future occasion the interesting features on the floor oí Hqiparchv-* may be described.

CHAPTERS ON CURIOUS CATERPILLARS.

AUGUST.

By J. R. S. Cliffohd.

AUGUST is very often a month of sunshine. and one also favoured with heavy showers of Tain. The first is agreeable enough to many of the caterpillars now feeding, though there are some so squeamish as to resort to various concealments during the heat of tho day, preferring to feed while the early dew studs the leaves, or at night, when they can come abroad with the additional advantage of not being in danger of thenlives from some vigilant bird intent on filling its own crop, or intently engaged on the more benevolent business of providing for the wants of a helpless brood. There are some caterpillars, too, which seem indifferent to the rainfall—in fact, perhaps rather enjoy a shower bath than otherwise ; while again, in many species, the dislike and avoidance of moisture isnotable. After a summer's rain, we shall find numerous caterpillars, especially young and naked ones (for the hairy and spiny individuals have tho best of it at those times), sadly bedrabbled, or even lying half dead, while a certain portion are actually killed; and there is no doubt the numbers of some destructive species are thus diminished by drenching showers or long rains, to the advantage of vegetation.

What are commonly called by collectors the Dagger moths (from peculiar markings found belonging to the very deficient family of the Bombyces. Some of them are amongst the earliest on the wings of some species) belonging to the genus Acronyeta, and the family of the Noctvuc, in the caterpillar state remind one rather of those captures made by the young seeker of caterpillars, who is surprised at the emergence of a moth or moths not at all resembling his expectations. The most common of all is tho Grey Dagger (A. Pei), which occurs all over the country, and even in the heart of towns. On the back of this caterpillar are two humps—the first being long and horn-like, on the fifth segment, and at the extremity of the body is another, shorter and broader; the former of these is deep-black, covered with hairs; a yellow stripe runs down the middle of the back from the third segment, ending at the anal lump, and on each side of this is a black stripe of the same breadth; enclosed in this stripe on every segment from the fifth there are two red spots and two white warts; beneath this black stripe again there is a grey one on each side, tinged with red, and hairy. The head is black and shiny, like that of the well-known Tiger caterpillars, often called "Woolly Bears." The caterpillar of this species ie by no means particular as to its food, roving about in gardens from plant to plant, and from tree to tree, sometimes continuing to feed until late in autumn. Closely allied to the preceding is the so-called Dark Dagger (A. trident), though not noticeably darker; indeed, in the perfect state the two species are so alike that our greatest entomologists find it no easy task to distinguish them. The caterpillars, however, are markedly distinct, and of tho two, trident is apparently the scarcer species, though widely dispersed. The body of the caterpillar is black, having numerous orange and white spots disposed in a regular manner ;there is a narrowish orange-yellow stripe along the back from the sixth to the eleventh segment. Thero is a hump, as in trident on the fifth segment, black on the top but grey behind ; and on the twelfth segment there is a slight hump, with a snow-white mark on its top; behind this is a horn pointing backwards. There is a stripe along the sides containing the spiracles which is mottled with yellow, not grey, as in the preceding. This caterpillar is most partial to the blackthorn and whitethorn, and remains out, like its relative, for some time; the cocoon is generally spun in a crevice of the bark of кото tree. The sycamore is not a tree favoured with many insect dwellers, but one of the «ievourers of its leaves is the caterpillar of the Sycamore Dagger (A. aceris), which generally prefers to feed on the higher branches, also eating occasionally the leaves of the horso chestnut. When alarmed it assumes one of tho positions shown in the figure, and remains unmoved for a good while. The body is of a dull flesh colour, but this is scarcely noticed, owing to the long hairs which clothe it, and which, though varying in tint, are usually yellowish-red; some of these hairs form a series of "faciclcs," or brashes, each series having nine. Along the back we find a series of white spots bordered with deep black. The head is black with a white mark like the letter V, the spiracles and legs are black and the

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be found sometimes in good condition, on a trunk or paling, making its way to the earth, where it usually spins its cocoon in some dry nook, not appearing as a moth till the spring, which is the case with others of the genus. Another hand some caterpillar, not very frequent, is the Coronet (A.ligustri). This refuses to roll itself up when alarmed, but moves off with some speed. The head is of a very light green tint, and appears almost transparent ; the general colour of the body is also green, while down the middle of the back is a narrow white stripe, and below this another broader stripe of yellowish-white, which docs not kowever reach to the spiracles; on each segment there are a few silky bristles. Though called after the privet in its Latin designation the caterpillar before us seems to prefer to feed on the ash, near the roots of which the chrysalis may be found in some slit in the bark or hidden in moss. The cocoon turns black after a certain time, and is somewhat of a gummy texture. On the alder there is sometimes detected, though very rarely, the caterpillar of the Alder Dagger (.1. Alni), and this is remarkable not only from its scarceness, but because it curiously diners from the other caterpillars of the genus. The head is very glossy, and as broad as the segment to which it is united, black in colour. The body is purplieh-black, and along the back are situated a series of yellowish-white markings, which are sometimes absent, wholly or partially. The most singular circumstance connected with its appearance is that on each segment there is what has been called a " process " or "appendage," black and flattened, and unlike anything seen in other British caterpillars. In confinement this caterpillar has been found to eat other leaves besides those of the alder. The cocoon is compact, and usually concealed.

Our largest native caterpillar is to be found of its full dimensions at the end of July or during August, and he who has once seen it will not easily forget its appearance and proportions. Though most partial to the potato, it has sometimes been detected on the privet, the jessamine, and several other plants. Whatever its food it usually hides from view during the day, going to the surface of the earth, or to the thicker portions of some bush or shrub. When at its greatest size, the caterpillar of the Death's Head is nearly five inches in length. It has long been noticed that the moth had the power of producing a peculiar sonnd, so stridulous as to be sometimes called a squeak, and somo of those who have reared the caterpillar aescrt that it has also а rather similar faculty, only the noise resembles more the snapping of electric sparks. Others have failed to perceive this, and have questioned the truth of the statement. This caterpillar, like so many others of the Sphinx family, has an anal horn, which is rather rough, and has a double bend downwards at its junction with the body and then upwards again close to the tip ; in colour it is yellow and black. The head, which is occasionally almost withdrawn beneath the second segment, is orange-yellow, with a brown stripe on each cheek, commencing at the crown and running down to the mouth; the colour of tho body is rather lighter, and the yellow passes into green on the under side; on the three segments immediately behind the head there are no spots; but the other segments are highly ornamented—first, with a number of oval deep purple spots, and

secondly, with markings in the shape of the letter V, and these are of a dull violet hue. The quantity of leaves consumed by these caterpillars when in their last stage is extraordinary, and having arrived at maturity they enter the earth to a considerable depth and there construct a oeil composed of a gummy substance mingled with enrth. Not unfrequeutly, when potato-helds are dug over, the caterpillars and chrysalides are t nrned np, the former being called " locusts" in tins midland and northern counties. The chrysalides thus got are sent sometimes to London or to other towns for sale, and вото years they may 1 ie purchased at a moderate rate by those who may be curious to see this magnificent moth emerge. The getting the moth out is no easy matter, for very often the chrysalis has received some unnoticed injury when unearthed, and afterwards the temperature and the moisture or dryness of its condition must be nicely adjusted in order to secure its emergence.

Considerably less in size, though still to be reckoned a large caterpillar, is that producing the Privet Hawk-moth (Sphinx ligustri) this is so iciaspicnous on the privet hedges that those not insect-hunters sometimes see it, and pause to admire its beauty, as I have myself noticed in the vicinity of London. This has also a horn, pointing backwards, black and shining above, and yellowish beneath. The ground colour is a delicate green, and along the sides aro seven stripes, which are purple and white. A few days before the caterpillar is adult, the colour of the stripes fades, and the green of tho rest of the body turns to a brown. Entering the earth, the caterpillar finally scoops out a cell, in which it becomes a chrysalis, on the front of which there is a sort of beak, which contains the proboscis of the future moth, whose appearance on the wing is usually in June. Feeding on the lime or the elm, and in some places not rare, we may discover during August the caterpillar of the Line Hawk-moth (Smerintlms Tilia:). It is rather partial to the higher branches of trees, whence a brisk wind occasionally dislodges it, and sends it to the ground, not advantaged by the fall. But, like others of the family to which it belongs, it grasps the branch or twig on which it rests with great tenacity, and may be injured if torn suddenly from its hold. This caterpillar is shagreened all over, and sprinkled with yellow* dots, the ground colour being green; on the sides are disposed the seven stripes so frequent amongst the Hawk-moth caterpillars. The anal horn is blue on the upper surface and yellow underneath, while close to it there is a very singular plate or circlet, purple, edged with yellow. This is not found in the two other caterpillars belonging to the вате genus (Smerinthut), and which are commonly known as the Eyed Hawk-moth, and the Poplar Hawk-moth, though in other points they are not dissimilar. The caterpillar of the Eyed Hawk is most partial to willow, occasionally visiting fruit trees, and in this the horn at the tail is blue, which at once distinguishes it. That of the Poplar Hawk is generally more of a yellowish cast, and along the sides close to the spiracles there runs a series of red spots.

Some curious caterpillars of butterflies arc feeding in the month of August, and several belonging to the Vanrtta genus are full grown at this time, or a little earlier. It is singular that several of these live exclusively on that apparently unpalatable and most abundant plant, the stinging nettle. Living in companionship almost throughout their caterpillar life (which only lasts from four to six weeks j we have the small tortoiseshell (V. Urtica), a beautiful insect as it sports from flower to flower. The caterpillars of this species vary much in colour, being all shades of grey, mingled with yellow, green, or black. Tho head is shiny and black, while the claspers are qnito pale. The whole body is covered with what are called compound spines. That of the peacock ( V. la) is also social until the last change of skin. Here the ground colour is a rich black, not variable, and freckled all over with white dots, which seem to be arranged in rows. The spines are long and compound. Rather hermit-like in its habits ie the caterpillar of the brilliant and fearless Red Admiral (V. Atalanta), and not only does it choose to live alone, lint draws the leaves elightly together with silken threads as an additional security. This is very dark grey, or sometimes reddish-black, slightly marked on some parts of the body with white, and with a wavy yellow line along each side. The spines are of a reddish-brown. Sometimes on the nettle, but more frequently on the thistle or the burdock, protected by a slight Bilkou web, dwells the Painted Lady caterpillar (V. Cardui), similar to the preceding, but darker, and having usually more stripes. Singular as this caterpillar is, like many others, it gives no indication of the splendidly adorned winged insect it is to produce. In some years the Painted Lady is scarce, and the cause is doubtless a mortality amongst the caterpillars, as they appear to be liable to severe attacks from insect enemies. The caterpillar of the large tortoiseshell is little known in this country. Unlike its brethren, it rejects low plants, and climbs tall trees, especially the elm and the sallow. This is also spiny, and of a dull yellow hue, with a black stripe on each Bide.

Some of the Geometric caterpillars to be seen this month ere large and singular. That of the Peppered Moth (Amphydasis betulpria), when reposing, stretches out its head in a peculiar manner, haviug almost invariably a silken thread passing from the month to some part of the branch, and thus securing it against a sudden shock. This caterpillar has the head notched on the crown. The ground colour varies much, even in individuals from the same batch of eggs, some being clay-coloured, others greenish or brownish. There are two conspicuous red spots on the back of the ninth aud twelfth segments, and six similar ones along each side. Th« food is a variety of trees; in the birch, whence it has its name, it is rarely found. The chrysalis is buried beneath the earth through the winter. The Great Oak Beauty (Boarmin roboraria) is developed from a rather handsome and stick-like caterpillar, having two humps on the sixth segment. The colour is a chequered tinge of black and white, and down the middle of the back there is a slender thread. Oak is the chief food of this choice caterpillar, which has been taken formerly in Richmond Park, and still occurs in the New Forest, and a few other places in the south of England.

PLATINISED MIRRORS.

THE cost of large mirrors, to whatever cause it may be due, is undoubtedly larger than what the nature and price of the materials of which they are composed would lead one to imagine. We are uot now alluding to a framed minor, but simply to a givtn area of glass and quicksilver. It has therefore been proposed, some years since, to dispense with the silvering and substitute a preparation of platinum. At Aisne, this system, which was introduced by M. Dode, is in full operation, the basis of the process being the chloride of platinum. After being thoroughly well cleaned, the glass receives the liquid, it is then moved about iu various directions, so as to ensure the layer or film being uniformly spread over its surface. The liquid has a slightly oily character, as it is mixed with a ^quantity of essenco of lavender. It spreads gradually, and dries without leaving behind the faintest tint of auy kind. The platiniferous compound is made as follows. About three and a half ounces, avoirdupois measure, of thin platinum ribbon are dissolved iu aqua regia, dried in a sandbath, care being taken to avoid the decomposition of the newly-dried chloride of the metal; fjpread out upon a glass surface, and tho rectified essence of lavender added, little by little. So soon as nearly fifty ounces of the essence has been poured upon the chloride, the mixture is placed in a porcelain vessel, and left completely undisturbed for eight days. At the expiration of this time it is decanted aud filtered, and after a further period of six days, it is again decanted. As a Hux for this mixture, certain proportions of litharge, borate of lead, and essence of lavender are employed. . These are all mixed up and thoroughly incorporated; and the liquid is then ready for application. Mirrors prepared in this manner are exceedingly brilliant, and the cost does not exceed one shilling per square yard of glass, a notable degree of cheapness compared with the price of the silver mirrors.

DOES ALCOHOL WARM THE BODY ?—Professor Bing has cmiio to tlie following conclusions on this subject:—1st. That alcohol loners the heat of the body, and that it preserves life in febrile affections, whore the temperature rises very high, by its antipyretic properties, tlnd. That extreme depression of the vital powers in febrile cases is most frequently dependent upon the temperature of the blood, and passes oil when at falls. 3rd. That the number und strength of the contractions of the heart always rise under the fuse of alcohol. Whenever, therefore, such an effect would be injurious, alcohol would be an improper remedy. 4th. That in all probability alcohol lowers the temperature by the retarding influence it exerts over the oxidizing process.

EE VIEWS.

Contribution* to tin' Mineralogy of Victoria. By Gkouoe H. F. Uleich, F.G.S. Melbourne: John Ferres. 1870.

THIS little pamphlet contains a list of the minerals hitherto found in the " richest goldbearing country in the world." Victoria possesses not only tho very essence of mineral riches, but it is likewise the home of several minerals which are new to science ; but taking into consideration the small number of different mineral species hitherto discovered in tho many hnndred of auriferous lodes opened up throughout the country, and comparing the result with the dozens of fine minerals occurring in the ore-lodes of Cornwall, Saxony, the Hartz, &c, the reward for miceralogiciil research appears rather a meagre one.

The list includes bismuth, stibnite, the valuable cassiterite, and magnetite; and among precious stones the sapphire and oriental ruby, topaz, garnet, and opals; while Selwynite, pyrophyllite, and talcosite are among the more recent minerals known to science. Speaking of the rubies hitherto discovered, the author says that several have been found of a size worth cutting, and one iu particular, presented to the National Museum, a small, but nearly perfect crystal, would, from its line \ iolet colour, be ealledby jewellers the oriental amethyst. It resembles the quartz amethyst, but its distinction from the latter is easily proved by its more acute pyramid, far superior hardness (scratching topaz), and its action npon the dichroscope. It shows before the blowpipe, on and after strong heating, a behaviour generally recorded for the spinel ruby, but which is also characteristic of the oriental ruby; it turns quite a dark opaque, but on cooling becomes green, then colourless, and finally resumes its original red colour.

This book will doubtless be of use to crystallographers, as correct figures of the more interesting crystals are given, together with accurate measurements of angles for the determination of the indices of the pianos of some of the new crystals. As a record of tho more recent discoveries of the minerals hidden in one of our most distant colonies, this little brochure must be of interest, if not of value.

Pcirtntr's Comprehensive Specifier. A Guide to the Practical Specification of every kind of Building-Artificers' Work. Edited by William Youno, Architect. London: Longmans. This handy work of reference will doubtless save the architect and builder some trouble and time, containing, as it docs, the various items necessary to form a specification, which are printed iu distinct paragraphs, and marked by consecutive numbers for facility of reference. There is also an appendix, which contains a specification for repairs and alterations, together with a short form of building conditions and agreements. Those of our readers who are aware of the disputes which often arise between architect aud builder, or between the former and his employer, through some item of a specification being insufficiently or wrongly described, will readily understand and fully appreciate the value of such a concise vade-mecum as this little volume.

The Manual of Colours and Dye-Wares; their Properties, Applications, Valuation, Impurities, and Sophistications. By J. W. Slater, Author of the "Handbook of Chemical Analysis for Practical Men." London: Lockwood & Co. The title of this book almost renders nnnecessary any elaborate review of its contents; and all we need say is that Mr. Slater appears to have done his work well, and has really made his handbook what its title asserts it to be. The object of this manual is to furnish an account of the chemical products and natural wares used in dyeing, printing, and the accessory arts, their properties and applications, the means of ascertaining their respective values, and of detecting the impurities which may be present. Recent years have been so fruitful in novelties, and have witnessed so great an enlargement of the resources of tinctorial art, as to render older authorities defective and, in some measure, obsolete. Mr. Slater's work is a strictly scientific manual, as he relies on the chemical methods of determining the nature and value of the different dye-wares, rather than upon the judgments formed by brokers aud consumers after a cursory examination of the article.

The Quarterly Journal of Education. London:

T. J. AUman. July, 1870. The latest number of this unpretending quarterly is now before us, and we are astonished at the amount of interesting matter it contains. That a journal devoted to the interests of schoolmasters should be well written cannot occasion surprise; but that it should contain such papers as are printed in this magazine is really more than could be expected. Thus we have an article on "Political Economy as a Means of Education," by Professor Rogers; a paper by A. R. Hope, the well-known author of the "Book about Boys," "Stories of School Life," &c.; and a short description of the '• State of Linguistic Studies in France," by J. K. Morell, LL.D. There are also some useful notes on " The Twelfth Night," which will interest all students of the language and afford some mental pabulum to lovers of Shukspeare. Several other interesting subjects are discussed, aud the columns devoted to correspondence are, as might be expected, replete with matter for thought, although naturally enough connected principally with schools aud schoolmasters. One letter in particular wo would commend to the attention of those of our readers who have any notion of sending their children to boarding school. There is no doubt that Dotheboys Hall has been greatly changed for the better, but the facts related in this communication show very clearly that there is still ample room for improvement. At the present time, while the education question is so fiercely debated, there is matter in tliisjoiirmd of Education to interest everybody, and we cordially commend to our readers a periodical so ably conducted.

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BOTH the local specific process and the fever have a tendency to terminate in the restoration of the sufferer to health, without any intervention of the medical art. But at the termination of these conditions a state o! health, often wretchedly below par, is left behind. Scarlet lever frequently destroys the drum of the ear, by extension of Uie sore throat backwards into the Eustachian tube, aud there sets up an ulceration by which the patient's life is in constant jeopardy: at any time, too, from the fading of the rash until a month afterwards, that fatal form of dropsy, called scarlatinal dropsy, may supervene on the slightest exposure to cold. Measles, chicken pox. and whooping-cough, very slight in themselves, leave behind a predisposition to a most fatal complaint, the deposit of tubercles in every part of the body. In grown-np people the brunt of the disease usually falls upon the lungs, and it is then called consumption; but in children the disease is spread more generally throughout the system, the brain auJ other organs suffering quite as much as the lungs. This disposition to tubercle arises after these three diseases without any previous hereditary taint or inclination whatever. The zymotic diseases, then, are not the harmless ailments which the public think them to be, but even the mildest may leave behind tho seeds of a malady which, sooner or later, will destroy life.

The circumstances under which zymotic diseases are enabled to spread ore the following. First of all, the zymotic principle itself must be present; next, a condition of the atmosphere or of the surroundings, favourable to the spread of disease; small-pox and scarlatina are always present in England, yet it is only occasionally that the sporadic cases multiply so greatly as to become epidemic. Thirdly, a medium for the conveyance of the contagious matter to the individual or some part of hiin, where it can easily enter Ms blood; iJ seems probable that niost of the zymotic poisons enter by the mouth. Lastly, an individual in a stak fit to receive the germ of the malady, and allow it to multiply.

Knowing that these four conditions are necessary for the spread of these contagions diseases, the means at our disposal for their prevention will be shortly alluded to. With regard to the zymotic substance, the agent which most effectively destroys it is heat. In Egypt, the spread of the plague is always arrested after St. John's day, from the intense heat which then arises. A temperature of 120° Fahr. will destroy the contagious material contained in clothes, papers, &c, thus most conveniently disinfected, the most delicate fabrics remaining uninjured after exposure to so low a te mperature. Several chemioal agents are said to have the power of altering or changing the composition of the contagious material Bo as to render it innocuous. Amongst these are especially to be mentioned carbolic acid, chlorine, and nitrous acid.

The state of the surroundings is very important, but unfortunately little is known, of the meteoro

* Written by J. WiCKiUH Lsoo, M.D., and extracted trom The Student.

logical changes which accompany an epidemic. A temperature of No Fahr, seems to check the spread of some contagious diseases, but the whole of our information on this point is most meagre. One of the surrounding conditions is known to be extremely important—the dilution of the contagious nmterial with fresh air—this is without doubt, the most important agent that we possess in checking the progress of a contagious disease. Free, efficient ventilation of a house will often protect its inmates from Wfection from without. The media for the conveyance of disease have been spoken of previously. A predisposition on the part of the individual who is exposed to the contagion ; for not every one exposed, is infected. Some persons seem quite incapable of receiving the zymotic diseases during the whole of their life; while, on the other hand, certain conditions of the system predispose to them; mental anxiety, worry,and trouble of any kind render a person peculiarlyliable. So do fear of taking the complaint, a poor state of health at the time, great bodily fatigue Anil exhausting labour, above all, the fasting state. A person who has not eaten for hours will be far more likely, other conditions being equal, to be infected, on exposure to contagion, than one who has just taken a meal of meat and wine. We cannot always control our emotions or secure it tranquil and happy frame of mind; but at the worst, most of us can afford a dinner add a dose of stimulant. After exposure to infection, a glass of sherry or brandy and water, is said to prevent the complaint from taking root; it would always be well to try this remedy when a person has been near a source of contagion.

Amongst the poor, the want of good food and clothing, the mdilferent'ligbt which does not allow them to see the dirt about them, aud which they therefore do not remove, the overcrowding and bad ventilation, all render them exceedingly predisposed to the acute specific disease. Accordingly we find that an outbreak of zymotic disease always makes head among the poor first ; amongst them it gathers its strength and multiplies its points of contagion before it attacks the rich man's family. Indeed, there is one disease—typhus fever—which is unknown except among the extremely destitute; clergymen and doctors occasionally die of it, their profession obliging them to visit the sick poor, but under no circumstances does it ever gpitad among people moderately well to do.

After a consideration of the preceding remarks, the question, "How may zymotic diseases be prevented?" may be more easily answered. Individual action can do little ; it is to the State that we must look for efficient interference for the suppression of these complaints. With our English notions about the liberty of the subject it will take years of active teaching and reiteration before any government will be sufficiently interested to make laws which will perhaps seriously interfere with the present prerogative of every English subject to spread infection. It has taken seventy years for the English Government to realize the value of Jenner's great discovery, and to take steps to protect the community against periodical outbreaks of small-pox. It is to be hoped that another seventy years will not elapse before something is done to stop the spread of scarlatina, measles, or typhoid fever. Laws compelling the drainage and water supply to be at least effective, and forbidding the frightful overcrowding of dwellings which now prevails in every large town, ought to be made; every case of zymotic disease ought to be watched by officers of health, since that one case may become the centre of extension to the whole town, country, or even kingdom.

Individuals may, however, do a little in preventing these complaints, especially in their own households, but their exertions can scarcely reach beyond this. In the first place, let the water that is used for drinking be most carefully seen to at all times. No one should buy water of a company the purity of whose source of supply is at all questioned, for water that looks, smells, and tastes perfectly good may convey the deadly poison of cholera or typhoid fever. The same consequences ought to follow the sale of unwholesome water to the public as follow the sale of unwholesome meat or vegetables ; or, rather, the punishment should be greater, because the effects are more widely spread.

One of the most important means of prevention is also within the reach of individuals ; it is quite simple, needing no apparatus or chemicals, and is the free and complete ventilation of all rooms aud passages by means of windows opening on the external air, assisted, where there are opportunities, by fires in open grates. This method yields to none in efficiency; it is of far more use than any chemical means of disinfection, useful though these may be; the only effectual plan is complete and thorough ventilation. When a member of a household has been seized with a zymotic disease it is most important that no communication should be held with the sick room other than is absolutely necessary; everything which comes from the sick bedside, or which has approached the sick man should be immediately destroyed with fire. When this is impossible from the nature of the article, as porcelain or glass, it should be placed in boiling water for several minutes, as soon as its contents

have been got rid of. The disposal of water and other fluids which have been used by the sick is a matter of воше difficulty. It is without doubt in the highest degree immoral to throw such refuse into a drain, whence it may easily pass on and infect others; the best plan seems to be to mix all these fluids with a solution of chloride of zinc, or carbolic acid, and then to have them deeply buried in the earth with a quantity of disinfectants, far away from any wells or sources of water supply to any human habitation. If the refuse materials are more solid than liquid, they should be completely destroyed by fire.

A low degree of civilization sets a low value upon individual human life. If we compare the thousands of pounds lavishly spent by Government, where cattle alone were concerned, with the small sums given grudgingly for the prevention and investigation—the first step in the prevention—of human disease, it will bo seen how hollow our boasted advance really is. The lives of cattle must be protected because they are valuable property; the lives of men are apparently of little or no account. So long чш 'the poor remain in their present wretched and Unhealthy condition—a very poor population »nay 'yet be healthy—aud so long as the death-rnte exhibits little or no decline in each succeeding year, so long are we on the moral level of barbarians in disregard for human life. This deep stain on modern civilization, the entire neglect of the sanitary condition of the poor, can only be wiped away by a great effort on the part of society in general, by the framing of laws, which shall be no half measures—the eiirse of English sanitary legislation—but which shall effectually and at once remove this evil from amongst us.

THE APPLICATION OF PHOTOGRAPHY TO MILITARY PURPOSES.

MODERN warfare may in many respects be considered as so many applications of science. Not only is war matériel designed and manufactured nowadays upon the most approved data, and according to theories worked out with mathematical accuracy, but a largo section of our soldiers are educated in such a manner as fully to appreciate the value of their resources, and so to overcome difficulties which years ago would have been regarded as impossibilities. No instance demonstrates this more satisfactorily than the recent Abyssinian expedition, which, whatever may be said of it as a campaign, cannot but be regarded as one of the most wonderful feats of engineering accomplished in modern times. The nearer warfare approaches perfection, the more decisive, and therefore less cruel it necessarily becomes, as witness the brief duration of the ware of late years on the Continent; and for this reason the improvements in warfare effected by science cannot by any means be regarded as a misapplication of knowledge.

Our present remarks bear reference to the applications made of a very modest branch of science, if science, indeed, it can be called, our object being to demonstrate the many uses made by the War De partment of photography. In the special applica tion of this art-science to military matters, our Government is certainly in advance of others, if we except, perhaps, that of Franco. No less than three establishments have been organized in connection with the army in which photography is extensively practised, the most important of them being the General Establishment at Woolwich; but, besides these, there are again many Royal Engineer stations, both at home and abroad, which are furnished with photographic requisites and employ the camera for divers purposes. At Chatham, the photographic establishment assumes the character of a school of instruction, at Southampton it forms an adjunct to the Ordnance Survey Office, while at Woolwich, of which department we desire more particularly to speak, the duties performed by aid of the camera are as various as they are numerous. For registering patterns, recording experimental results, imparting military instruction, and for other purposes too multifarious to enumerate, photography is extensively used, the faithful accuracy of sun pictures, as likewise the facility with which they are produced, causing the art to be eagerly employed in any way where it can be made available.

As an example of the value of photography in instruction, we would cite an interesting series of pictures taken to illustrate ordinance drill. This series comprises upwards of one hundred views, and demonstrates the practical working of the various kind of gnus, mortars, rockets, &c, in tho service. One picture, for instance, will illustrate the command " Prepare for action ;" a gun will be shown surrounded by a group of artillerymen in the positions they have been instructed to occupy on the issue of that order, each man having his respective number attached to his cap as a distinguishing mark. The next illustration in the series is probably that of '• Lead," and the next again "Fire," both of which will represent the change in position of the men, as one operation succeeds another, and the various duties performed in turn by each

gunner or number, for it must be remembered that in gun-drill every man is told off to a particular number and entrusted with a separate and distinct duty. Thus, on the promulgation of any new system of drill, or of any modification in the method of working, it is merely necessary for the military authorities to forward pictures of this kind to the different instructors, who cannot fail at once thoroughly to understand the new exercise; and even the rawest recruit who had assigned to him a certain number at a gun would see at a glance the exact position he is to occupy by a reference to the photographs.

Another not less striking instance of the importance of photography in this connection may be given. At the outset of the Abyssinian campaign it will be remembered that several thousands of packsaddlcB were required for transporting war materiel into the interior. These packsaddles Were made in and sent direct from England to Anuesley Bay, so that the troops coming from Bombay knew nothing of their construction, nor of the method in which they were to be packed. This ignorance in the hurry of affairs would have been of serious consequence (for the military packsaddle of the present pattern is a somewhat complicated contrivance) had not the authorities at home been fully alive to the subject and foreseen the threatening difficulty. A mule at Woolwich was harnessed and packed, after some experience had been acquired m the matter, in the most suitable and approved manner, and the animal then carefully depicted by the aid of the camera; the disposal of the harness and trappings and the correct way in which the packages were to be carried, were thus clearly shown in a photograph, numerous copies of which were immediately sent out to Annesley Bay and distributed among the officers of the QuarterMaster-Gencral's department.

In recording experimental results photography again fulfils a duty which could not be discharged so rapidly and impartially by any other means. The Moat iron-cased shields and armour targets built up of metal plates of different thicknesses, and then fired at by shot and shell of all descriptions, are carefully photographed after each decisive experiment, and record of indisputable accuracy thus obtained. With a picture before us of a target, constructed to represent the side of an armour-plated vessel which has been experimented on, we can at once form an accurate estimate of the impression made upon the iron wall by shot of different calibres, while rear and side views of the structure will show plainly the amount of damage which the backing or skin of the shield has suffered. As may be imagined these prints form important illustrations to tho written reports made from time to time to the War Office authorities.

The photographing of newly adopted government patterns, whether in the shape of guns, carriages, wagons, mantelets, tents, &c. is also an important section of the work undertaken at Woolwich, as likewise that of producing pictures relating to army equipment, such, for instance, as demonstrate the setting up of cooking apparatus, disposal of ambulances, refitting of ordnance in the field, Arc. There is, moreover, the pursuit of photo-lithography to be mentioned, by means of which designs and sketches are copied and transferred to stone for printing off in the ordinary manner.

The subject of working photography in the field is a matter to which much attention has been given at the general establishment, for it will be readily conceived that tho simplest and most effective methods of working, Rs likewise the different uses to which the camera may be put during warfare are questions of very serious study.

The photographic copies, many thousands of which are annually produced and distributed over all parts of Her Majesty's dominions, are not now printed upon silver paper in the ordinary way, but by the so-called carbon or autotj-pe process, a method which produces prints of an absolutely permanent character. Ordinary Bilver prints are always liable to become faded and drained after the lapse of a few years, owing to the presence in the paper itself, or in the atmosphere with which it comes into contact, of sulphur compounds which attack the metallic silver composing the image. In the carbon pictures, however, no silver at all is present, the composition of the image being a mineral pigment in combination with an insoluble chromium.

Our description of the General Photographic Establishment at Woolwich has been very brief indeed, but enough has been said to show to what an important extent the art is employed in connection with the War Office; the department which we have described is a branch of the chemical establishment of the War Department, which was first organised in 1854, by Mr. Abel, and has gradually become intimately and indispensably connected with every branch of the military service.—Nature.

THE VARNISH TREE.

THE beautiful black varnish which is so much admired the world over is the production of a tree which grows wild in Japan—and China as well.

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