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THE DEFENCES OF

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PARIS.

HERE is probably no subject connected with the war which is more interesting than the power possessed by Paris of standing a siege. We have, therefore, thought it well to place before our readers the accompanying map of Paris, showing its fortifications. The drawing has been prepared from the latest maps which can be obtained, and is as accurate as is consistent with the scale.

Paris is situated, to use a military term, à cheval on the Seine, near the junction of this river with the Marne, the latter river covering the city on the east, while a bend of the former protects the western side. The fortifications consist, first, of a chain of detached forts or fortresses command

ing the rivers, and, secondly, by an enceinte continué running right round the city. The bastion system of Vauban is adopted throughout.

The exterior line of defence commences at St. Denis on the north, and extends to the Marne at Nogent, a distance of about eight miles. It consists of nine fortresses, and opposes the direct advance of troops from Germany. On the south Paris is covered by a line of six forts, reaching from the Marne to the Seine, a distance of about seven miles. These complete the defence of the south; four are pentagonal and two quadrilateral. They are built of substantial materials, and contain bomb-proof barracks, and have casemated curtains. The third exterior line of defence is eight miles long. It does not consist of a chain of forts, but of the great citadel, Mont Valérien, which

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serves as a tête-du-pont to the bend of the Seine, which covers Paris to the east. Mont Valerien is supported on one side by Fort d'Issy, and on the other by St. Denis. It is the most the river is 460 yards long, and the other four faces average 328 yards each. There is bombproof accommodation for stores and 4,500 men. The ring of detached forts, all of which will be casily found in our map, extends over 22

important work of the whole. The front toward

miles.

Within this is seen the enceinte continué, or continuous line of fortifications. This consists of no fewer than ninety-four bastions. The exterior sides average 328 yards per bastion, forming an enceinte of 30,840 yards, or nearly seventeen miles, probably the largest work of the kind ever executed. The cost was enormous-to judge from Marshal Marmont's opinion, was well spent. Marmont considered the fortifications of Paris "an event the most useful and important in the defence of France." The escarp of the enceinte is 33ft. high, the ditch being 82ft. wide. The distance from the boulevard to the enceinte continué averages about 1,093 yards, and that from the enceinte to the forts is about the same. So long as the forts are unconquered it will be impossible to bombard Paris from a less distance than about 7,000 yards, and even then the siege train will be under fire at a range rather too close to be pleasant.

In addition to these defences it is stated that earthworks are being raised from fort to fort, but we learn from private letters that these are of a very insignificant description, affording good cover, it is true, for riflemen, but not safe against even 6-pounder guns. It is stated that more than 1,000 guns can be placed in position; but this estimate, no doubt, includes a very large number of weapons which, however effective at close quarters, will be practically useless at long ranges.

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deductions from them; and whenever a violent adductor muscle, by snapping together its light storm was in progress, to decide in what direction valves, thus forcibly ejecting the water within and with what velocity it was travelling; determine against the water without, flits through, and somewhat places it would visit, and at what hour it would times even skips upon its native element, like an arrive and finally transmit the announcement aquatic butterfly. But no pedestrian does so in all immediately by telegraph to those places especially Mollusca-dom. Why then should not these pedate interested. Such a system could not be expected bivalves, the mussels, walk as others of their own to attain satisfactory results without a pretty large people do? "For want of brains!" says one. You number of well-selected stations, and especially are mistaken, sir. They have brains, the right without the service of a competent meteorologist kind too, and in the right place, a real pedal to superintend the entire system. The superin- nervemass, or ganglion; a little bilobed brain tendent should be well informed respecting the at the very base of the "understanding" itself, progress which has been already made in this that is, exactly nuder the foot, as was fabled of department of science; he should have strong a very agile dancer, that his brains were in his faith in the practicability of attaining useful results heels." by a system of storm-warnings; and he should have no other engagements which would prevent him from giving his whole attention to this subject, especially whenever a violent storm was raging in any part of the United States."

norning, and Pittsburgh at noon of the 17th,aving traversed the distance from St. Louis to Pittsburgh in some 18 hours, or at the rate of about 30 miles per hour. From the newspapers of the Following day it might have been quite as easy to race the storm on to the sea-coast, and perhaps to rather particulars of the damage to shipping which t caused. For several years the Smithsonian Institution aas been collecting meteorological observations from all parts of the country, and labouring to deduce rom the facts thus gathered the laws governing he phenomena of the weather and the climate; and the valuable results so gained can now be drawn ipon in inaugurating the new system of storm preliction and reporting. "The determination of the full details of this system will be arrived at," says General Myer, in a communication to the Secretary of War, "only after careful study of the modes already tested in other countries, and consultation with experienced observers, telegraph companies, boards of commerce, and business men, as to their application or improvement in our own. There will need to be the study and determination of the points for observation; the supply of instruments, and the facilities for their use; the exact observations to be made; the exact form and times in which, when made, they are to be reported; the points at which reports are to be collected and deductions from them had; the places at which and the modes by which these deductions shall finally be announced, by telegraph and signal, and so made useful to the public, for the benefit of commerce, by the warning they may give or the aids they may offer. It is a wise provision of the act," he adds, "that it enables the army to be thus extensively utilized in the interest of commerce, by the exercise of duties already established, and which will require but little additional outlay. It would be needless and unwise to enter upon large expenditures by attempting at the beginning too extended a scope for the endeavour. I would suggest, therefore, that action under the resolution be limited, until the best modes for its execution shall have been wisely determined."

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In accordance with this view, he asks for an ap

propriation, for carrying out the law, of the modest sum of 15,000 dollars, for the current fiscal year, ending June 30, and 25,000 dollars, for the next fiscal year, ending June 30, 1871. As showing that the scheme is regarded with prompt favour by the interests it is designed to benefit, General Myer mentions the fact that the favourable proceedings upon the subject of six boards of commerce had, at the date of his communication, and within little more than a week after the approval of the joint resolution, been received at the office of the chief signal officer.

Professor Joseph Henry, of the Smithsonian Institution, writing to General Paine in approval of the objects of his joint resolution, points out the following conditions as essential to the success of the proposed system:

"Ist. The points from which the telegrams are to be sent must be carefully selected and furnished with reliable instruments. 2nd. These instruments must be in charge of persons properly trained to make the observations. 3rd. The telegrams must be transmitted regularly to some central point at fixed hours of the day. 4th. They must at this centre be collated and their indications interpreted by persons having a competent knowledge of the laws to which the motions of the storms are subjected. 5th. I do not think the military posts as now established will be sufficient to fully carry out the plan; additional stations would be required. 6th. An appropriation would be necessary for the pay of the telegrams, furnishing the instruments, and the necessary superintendence."

And Professor Elias Loomis, of Yale College, author of a valuable text-book upon Meteorology, writes to General Paine upon the same subject at length. He says:

"It is believed that our knowledge of storms is already sufficiently precise to enable a competent meteorologist to furnish information which would be of great value to commerce, provided he had at his command a sufficient corps of observers scattered over a considerable area to the west and southwest, and also had the means of transmitting his warnings immediately by telegraph; and if such a system were pursued for several years, it could scarcely fail to conduce to more precise knowledge, which would render it possible to give more reliable and definite warning of the approach of dangerous storms.

Now, if seeing is believing, mussels can walk. We once saw a young brown mussel, of the species Modiola plicatula, about five-eighths of an inch in length, turn his foot to most excellent account. We had pulled the youngster's beard off, and then had deposited him at the bottom of a deep aquarium. The water was probably but poorly aërated, hence he was evidently ill at ease, and to our astonishment he at once began travelling over the pebbly bottom, then up the glass side, with the utmost facility and grace. The foot moved precisely as any univalve gasteropod would do, and with the same easy gliding motion. The movement was continued without interruption until it had reached the surface of the water, a distance of not less than 10in., which, added to the distance travelled over the bottom, was probably equal to 14in. At the surface it lost no time in spinning its byssus, which it fixed to the side for a permanent abode.

These coincident views of the two highest authorities in the United States upon all matters relating to meteorological science doubtless foreshadow substantially the actual working of the system when it shall have been fully established. In due time we may reasonably expect to see every lighthouse and other prominent and sightly point upon the borders of the great lakes and the Atlantic coast connected by telegraph with a central meteorological bureau, to which intelligence of an approaching storm can be simultaneously and speedily conveyed-to be in turn communicated, by means of a uniform system of signals, to all vessels within reach, in ample time to enable them to prepare for the coming danger.

That the results of the operation of this system will be in the highest degree valuable, both as regards the immediate practical object of protecting our commerce from disaster, and as furnishing an aid to scientific investigation in a most important direction, there can be no reasonable doubt.

MUSSEL CLIMBING.*

AN any one see a snail travel, and not ask

C mentally, "how it does it?" The method certainly is curious. A fleshy disc is protruded, and caused to project in the direction of locomotion; it is then spread out flatly, and while slightly adhering to the object over which it is passing, a contractile energy is exerted, and the little animal bearing its house is drawn onward. Thus by the repeated protrusion, expansion, and contraction of this soft organ, in due time its journey is accomplished. Because of this method of progression on ventral disc, all those shell-fish, or, properly speaking, molluscan animals, so constituted, are called by the systematists, gasteropods, a term which means ventral-footed. And in rank these gasteropods stand

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next to the most highly organized of the mollusca. But some of these shell-encased creatures do not travel at all. Take, for instance, the oyster, called a monomyary, because the valves are held together by a single muscle. This sedate bivalve once settled, probably never moves from that spot. But all the dimyaries, or two-muscled bivalves, well represented by the common edible mussels, possess a foot, which is not greatly unlike that of the snails. The mussel's foot, however, presents, in its class, the least developed condition of this organ, for it is a spinner rather than a walker; or, as Owen says, it is subservient to the function of a gland, which secretes a glutinous material analogous to silk, the filaments of which are termed the byssus," which often serves for attachment to rocks. He farther says, "in most dimyary bivalves the foot is an organ of locomotion." Some of the river mussels in babyhood spin a byssus with which to moor themselves against the currents of the stream. When "In order to secure the objects here contem- older grown this necessity is overcome, and the plated, it would be indispensable to have observa- capacity just mentioned is lost. Then the adult tions from a pretty large number of stations, at turns its foot into a ploughshare, and is dragged along intervals not exceeding one or two hundred miles, in the furrow it makes in the mud. The razor-shell and scattered over a region to the west and south- alternately bores downwards and propels upward, west of those points for which the warnings were the foot doing all the work. With the foot as an regarded as specially important. These observa- elastic spring the heart-shell leaps along. But the tions should include all the usual meteorological common black mussel, Mitylus edulis, and its deinstruments, but more particularly the barometer, spised neighbour, the brown horse-mussel, Modiola with the direction and force of the wind. The ob- plicatula, who ever saw them walk? Propulsion is servations should be made daily at fixed hours, and not always walking. The scallop with its large should be reported by telegraph to some competent meteorologist, whose business it should be to compare the reports without delay, and make the proper Naturalist.

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By Rev. S. LOCKWOOD, Ph.D. in the American

For its lively colours, perhaps ruthlessly, we had picked this little fellow out of a large family cluster, snugly packed in a hole in one of the piles of the dock. It was a large group of all sizes, literally bound together by the silken cords of-attachment shall we say?

A fellow captive was a full grown, black, edible mussel, torn from its anchorage, a stone near by, at low tide. We afterwards found ensconed in this black shell an amount of intelligence which filled us with astonishment. If his youthful fellow-prisoner could beat him at walking, he was about to accomplish the feat of climbing to the same position by means of a species of engineering of a very high

order.

In order the better to understand this singular feat, let us introduce it by the narration of some spider tactics we once witnessed. The insect had captured a large beetle, but could not get it to its web, and seemed indisposed to prey upon it away from its den. It had dragged the prey under the web, which was about two feet above. It ran up to a point close by its web; there it attached a thread by which it speedily descended, and then attached the other end to its booty. Again it ascended, affixed another thread, then descended and affixed to the prey as before. Each thread, in sailor phrase, was made taut. After a good many threads had been in this manner attached, each being stretched tightly, and each pulling a little, the weight was seen to ascend a small fraction of an inch. Again the threads were increased, and again the weight ascended a little more; until at last, after incredible labour, perseverance and skill, the little engineer had the satisfaction of success; for its well-earned booty, with one final, tiny jerk "brought up "at the desired spot. The explanation of all this is simple. Suppose we take a cord of the material known by the ladies under the name elastic, and attach it to an ounce weight. If but very moderately stretched it would certainly pull at least a grain. Supposing it to do that, a second one would pull with equal force, and it would be but a simple estimate to determine how many threads would be required to raise the entire weight. But enough of this. Now for the mussel.

Placed at the bottom of the aquarium, where it had been for a couple of days, it had succeeded in wriggling itself up to one of the glass sides of the tank. This accomplished it protruded its large foot, stretching it up as high on the glass as it could reach, this organ seemingly adhering very tightly. A little hole opened near the extreme forward end of the foot. This tiny hole was really the extremity of a folded or closed groove. Out of this a drop of white gluten, or mucus, not larger than the head of a pin, was exuded and pressed against the glass. There was then a slight withdrawing of the foot, simultaneously with an unfolding or opening of the groove, which contained, as if moulded there, the already completed delicate thread. This done, the partly contracted foot (not drawn into its shell at all, be it understood) was again extended, this time a little higher than before. The groove or spinneret was again closed, except the little opening on the surface of the foot, whence another little drop of mucus appeared, which also was pressed against the glass. Again the foot was withdrawn a little, the lips of the groove unfolded, and the moulded thread set free. This gave thread number two. Each was evidently set at considerable tension. And in this wise, thread after thread was formed and set. I regret that I did not record the exact number, but am sure that it was about twelve or sixteen, and the time occupied was between two and three hours, when loup went the mussel,

about three-eighths of an inch high. Yes, he was drawn up by his own cords. He was literally lifted from terra firma. Not at all suspecting what was to follow I mentally exclaimed "This little fellow knows the ropes."

There was next a period of rest. Whether it was due to exhaustion of material, and was meant to allow the secreting gland time to evolve a fresh supply or not, I cannot affirm; but may say that such was my belief, for after an hour or so it set to work again precisely as before, attaching a new cluster of threads. This cluster was set about gin. higher than the previous one. When this new group of filaments was finished, the same result followed, another lift of a fraction of an inch, but not quite so high as the first. I now suspected its motive-the animal was actually in this singular manner attempting to reach the surface. It wanted to take an airing, and was really in a fair way to bring it about.

While setting its third cluster of threads, I foresaw a serious difficulty in the way, and one against which the spider never has to contend. It was this: after the third lift had been achieved the threads which had accomplished the first lift had changed direction; that is, the ends of the threads, which had pointed downward when pulling up the mussel, were now pointing upward, and were actually pulling it down. Of course the lowermost thread or threads would exert the most retrograde traction. Thought I, "Sir Mussel-man, you will have to exercise your wits now." I rejoice to say that the ingenious little engineer was complete master of the situation. The difficulty was overcome in this way-as each lowest thread became taut in an adverse direction, it was snapped off at the end attached to the animal. This, as I think, was done by two processes; the one by softening that end of the thread by the animal's own juices, purposely applied, as the pupa in the cocoon moistens its silk envelope, when wishing to soften the fibres, so that it can break a hole through which the imago may emerge; the other by a moderate upward pulling, thus breaking the filament at its weakest point.

proceeded to declare I was nothing more nor less than one which had cooled down from a fused condition, something like iron slag; nay, it was even urged that I was older than any other rock, and the theorists mapped out an idea-which existed for many years after, chiefly owing to its remarkable novelty-showing how the whole universe was for. merly one great cosmical fog; that this diffused matter was condensed into snus, planets, and satel lites, each of which existed for ages in a molten condition, owing to the heat evolved during the process of condensation; that the exterior of each planet cooled during the time which followed, and that granite formed part or whole of this cooled envelope! Such in brief was the orthodox notion of my birth, little more than a quarter of a century ago. Shall I enlighten my readers a little as to the nature of my mineralogical composition? I feel sure that most of them are acquainted with it already, but, if only for form's sake, I must go through with it again. My name is of Latin derivation, and was given me on account of the grannlar character presented by my different minerals. Generally speaking, these are four in numberquartz, felspar, mica, and hornblende. Very frequently there are also traces of other minerals; but these are the commonest, and those in fact which make up my bulk. The quartz portion you may tell by its glassy appearance, and usually milkwhite colour; whilst another good test is its superior hardness. This mineral is almost pure silica, and is one of the most refrangible of known substances. It can with difficulty be slightly dissolved in hot water, under great pressure; whilst it requires a great deal of heat to melt it, and, generally speaking, some sort of flux to set it a-going. The next most abundant mineral in the constitution of myself and relatives (for our name is legion) is that called felspar. Your eye may detect it in any mass, by its pink or flesh-colour, whilst it is so soft that you may scratch it with your finger nail. It is owing to the unusual abundance of this mineral that I am sometimes so friable or "rotten," as the felspar decomThe next day our little engineer had accomplished poses, and then causes the other minerals to fall the wonderful feat of climbing to the surface by asunder, just as the bricks of a wall would if all ropes fabricated during the ascent. Without delay the cementing mortar were to decompose away, it moored itself securely by a cluster of silken lines In many districts, as in Cornwall, where granite at the boundary where sky and water met, and was comes to the surface and has been subjected to atthere allowed to enjoy the airing it had so deser-mospheric wear-and-tear for hundreds of ages, it is vingly won. Bravo! my little Mussel-man! No not uncommon to find the fine felspar washed into acrobat can beat thee on the ropes. a newer deposit. Such is the well-known" kaolin," or China clay of commerce. The chemical composition of felspar is more complex than that of quartz. For instance, although its commonest elements are silica and alumina,-the former the base of common sand, and the latter of clay, there are also contained in it more or less of soda and potash, lime, magnesia, and iron. Mica, the next commonest mineral I possess, is so well known as hardly to need description. All my readers are surely familiar with the small, thin, silvery-looking scales contained in almost every piece of granite. Its ingredients are much like those of felspar, only differently mixed. Frequently hornblende is a mineral entering into our composition, and my listeners will readily remember it from its black or dark olive-green colour. When it is very abundant, it produces a rock vary. ing from dark grey to black. A great number of what may be termed varieties of hornblende are known to mineralogists. Its chemical composition, generally speaking, is about one-half silica, more than a quarter magnesia, and little more than half a quarter lime: besides these, there are usually traces of iron, alumina, and fluoric acid.

And what are we to say to all this? Blind instinct, forsooth! Who believes it? The wise men of the ages have written as the tradition of the elders-byssus-bound," of our Mytilus. But it can make of its bonds mooring lines of safety against the storm, and with consummate skill can build a silken stairway into its own wished-for elysium of delight. It is some three years since the writer witnessed the facts here recorded, and to this day the sight of a mussel inspires him with profound reflection on the ways of Him who made these creeping things of the sea.

NOTE. It has seemed to the writer, that in the perfection of movement shown by the Modiola plicatula, as given above, a high stage of foot development is indicated, such as would hint at a grade out-ranking Mytilus e dulis. The figure inserted is that of M. edulis; but the

process of climbing is the same.-S. L.

THE STORY OF A PIECE OF GRANITE.
BY J. E. TAYLOR, F.G.S.

TH

HERE are few rock substances on the surface of the globe which have received more discussion and been more investigated than myself. I am somewhat proud of the attention I have received in this respect, for most of the leading geologists of every country, for the last century, have devoted themselves to the task of seeking out my antecedents. I am acquainted with a whole library of books, all most learnedly written, and various of them proving the reverse of the other, which have been penned on this inexhaustible subject. Even yet the question can hardly be regarded as finally settled. Every now and then some moot point or another crops up to engage the attention of philosophers, but, thanks to the progress of other sciences, the investigation of these is no longer confined to verbal expressions. It is not a little amusing to remember the hot discussions which were held over me at the beginning of the present century. Philosophers though they professed to be, the disputants resembled political squabblers more than anything else. One set declared I was born amid fire, the other that I was of purely watery origin. Each believed in their own ipse dixit, and, as nothing could be absolutely proved, backed their own opinions by personalities. Somehow or other the former sect, who were called Plutonists, got the better of the latter, who were termed Neptunists. (The origin of these phrases my readers will not find it difficult to understand.) But my Plutonic commentators carried their victory too far. Not content with proving that I was not a mere aqueous rock, they

I mentioned above that I had many relatives,
who were more or less nearly connected (I cannot
say by blood, but by mineralogical similarity of
composition). These take various names, on
account of their leading peculiarities. Among
these the commonest is porphyry, which takes its
name from the purple variety used by the ancients
in making vases, &c. This my hearer may know
from the large and distinct crystals, usually of
felspar or quartz, which are embedded in the
granular matrix. Through porphyry granite passes
into all sorts of allied igneous rocks, such as clay-
stone porphyry, clinkstone porphyry, felspar por-
phyry, and so on. When hornblende takes the
place of mica in the composition of granite, the
latter goes by the name of syenite; when tale
supplants mica, the result is called protogine. A
fine-grained compound of felspar and granite, with
equally minute scales of mica, gives to us the
varictal name of pegmatite. According to the
number of minerals entering into our composition,
I and my relatives are roughly classed as binary,
ternary, and quaternary granites. All this detail
of structure may sound very dry and tedious; but
it is absolutely necessary to go through with it, if
my listeners wish to be more intimate with me.
Although I have not a distinct recollection of my
birth (as indeed, who has?), yet I have more than
a suspicion that such elements as soda, potash,
lime, &c., greatly assisted as fluxes in bringing me
into my original molten condition. I have men-
tioned the great number of relatives which claim
near or distant kinship with me, and I have now

only to remark that their affinity to stud
been determined solely by the fe
stances attending their origin. I do thi
terly refute the idea that the first fo
the globe was a granitic one! I t
suaded it could not possibly have ta
I will give you my reasons by-and-by fee
ingly bold assertion. What that cos

doubt if science will ever be ali- %
But the fact that it was not granite das s
least invalidate the theory that every
and satellite was so condensed Ime
matter. This theory must rest on ette
and, singularly enough, additional fact: •
to its support every day. We have not:
idea of what the primitive rock or e
globe was. The antiquated notion t
have been granitic arose out of mist-
tions. It was found that, however d
stratified rock, whether containing fo
some variety or another of granite wa
Hence followed the hasty deduction, ti
one granitic crust encircled the fluid m
interior of the earth. It was show
quent rocks were themselves formed
wear-and-tear of this granite, how the
in many places covered up by its own driz
the so-called metamorphic rocks were the
formed as stratified deposits, but altere
present appearance through the intens
newly-created seas, along whose bottens-
been elaborated.

All this is wrong, and it behoves nie. descend from the region of pure hypothesis : of pure fact. It is just possible, speaking pa of all the varieties of my family, tast Pre may be oldest. This, however, has never to thoroughly determined. One of ET reasons t believing I could not have required any vET EX heat to reduce me to the molten condition, and the in this process the agency of water, as well as si heat, was necessary, is as follows-Many of the larger quartz crystals entering to my composition are hollow. Frequently the bons are best of less filled with water. Now, it is a known fact that molten matter at a white beat rectims its tempera. ture to be considerably lewe bere it can ena evaporate the water mecha urth it. It has been recently show that crystal matter which has undergone pare impoy fusha, has usually cavities in its crystals, natamne atd. but either stony matter or a kind e gas, and, in many cases, even a perfect vacuna Be the conclusion is arrived at that in the case of coursegrained granite, containing much quartz, there is actually more proof of the action of ester than d dry, ingneous fusion. It is more than prosle therefore, that pressure, heat, and water combed in the deeply-seated parts of the earths res would cause the rocks to be reduced to a kind paste, and that this paste would be some variety granite. I can hardly enter into the abstruse detai of the deductions which have been made from chemical and microscopical examinations of my and relatives. Suffice it to say they result 2 μ ing that pressure, and this, generally speaki overlying rocks stratified or otherwise, is a p liminary and indispensable necessity to the fam of granite; that, if pressure be absent or less that required, notwithstanding all the other? quirements may be present-such as heat, s of mineral ingredients, &c.-such a resulting BSKÝ rock would not be granite! It might be a 7277 of porphyry, or basalt, or greenstone, af pressure were removed, and the moltes allowed to cool in the open air, simply lava! From a microscopical examinati various granites, it has been shown that the the Highlands of Scotland indicate their b been formed under no less a pressure than of overlying rocks more than were the gro Cornwall. There is good reason for belie latter to have required at least 40,000, SÓ • pressure; so, in that case, the granites of th lands must have been formed when 669 overlying rocks were piled above them!

#5

these operations, but I assure my hearer
One is naturally astounded by the ma
little doubt as to the general correctn
deductions. In this way the minerale
struction of myself and others supplem
teaching of organic remains as to the in
antiquity of the globe! Nothing short of an
of time would have sufficed for all the cha
which have been rung upon it.
believe many of my granitic relations are noth
There is reas
more or less than re-melted stratified rocks.
their enclosed fossils! As these have been sh
depressed or submerged, so as to bring the lowe
seated portions within the influence of the earth
internal heat, they have been first metamorphos
into a similar condition to gneiss and mica-sch
and, if the sinking went on, have passed throu
this stage into that pasty condition which deprive
them of all stratified structure, and converted the
into what I am myself! Then succeeded a revers
of the movement: so that this granite would b
thrust slowly upwards with all the overlying strat
piled above it. The movement went
these were tilted into a continuous mountain-chain

on unt

r high and extensive table-lands. Meantime the ranite nucleus would form the heart of such Contains, the strata dipping away, as in the Himalayas.

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appear at her dark limb 6m. afterwards. On the
16th, Tauri will disappear at the bright limb at

I fancy I hear some of my listeners remarking-10h. 11m., reappearing at the dark limb at 11h. 7m. But if granite can only be formed under such Lastly, Saturn will disappear at the dark limb of the moon at 6h. 4m. p.m. on the 30th, and will emerge mmense pressure, how is it we find such large from behind the bright limb at 7h. 18m. reas of country where nothing else is to be seen?" Mercury is an evening star during September, atn the answer to this we have the gist of the argu-taining his greatest eastern elongation at 4h. 33m. in nent, and I would respectfully ask the special the early morning of the 8th. Having passed this he attention of my audience to it. Let them ask them- becomes apparently stationary on the 21st. On the selves where the materials came from to form the 16th, at 4h. 54m. p.m., he will be in conjunction with Laurentian, Cambrian, Silurian, Devonian, and, in the bright star a (Spica) Virginis. He continues in short, all the other subsequent formations? They the constellation Virgo all this month. He rises not could only have been formed out of the waste of long before 8 o'clock in the morning at the beginning still older and already solidified rocks. Each of the month, and soon after 7 at the end of it; setting t: formation, therefore, represents the amount of those periods soon after 7 p.m., and about -wear-and-tear which went on during the period 5h. 80m. p.m. respectively. He souths on the 1st at when it was deposited. If there had been no 1h. 33.n. p.m., and on the 80th at 14m. past noon. Venus is a morning star throughout the month, rising compensation against this levelling process, all on the 1st about 2h. 50m. a.m., and on the 30th about the prominences would soon have been worn down 4h. 17m. a.m., southing at 10h. 25m. a.m., and common level, and the elaboration of more 10h. 49m. a.m., and setting about 6h. and 5h. 20m. p.m. recent deposits been self-checked. But each sucon those days respectively. She travels from Cancer oceeding formation shows that this was not the case, into Leo during September, and is in conjunction with but indicates that the physical arrangements of our Regulus at 4h. 48m. a.m. on the 14th. She is in planet have been much the same through all time perihelion at 4 in the afternoon of the 20th. Mars is to what they are at present; that atmospherical also a morning star, and a little more favourably and marine wear-and-tear were counterbalanced by situated for observation than he has been; albeit he is upheaval from beneath; that the exterior force still an exceedingly minute and insignificant object. emanating from the sun and resulting in all these He rises somewhere about 3m. past 1 a.m. on the 1st, atmospherical effects, was exactly adjusted by the souths at 8m. past 9 a.m., and sets about 5h. 16m. native force of the earth, exerted from the interior p.m. On the 30th he rises about 0h. 48m. a.m., souths outwards. These two have been in equable counter-at Sh. 27m. a.m., and sets about 4h. 9m. p.m. He is in poise from the beginning, otherwise the great the constellation Cancer during the entire month; and life-scheme of our globle would never have had time in conjunction with 2 Caneri at 3 o'clock in the afternoon of the 1st. Jupiter rises on the 1st, about for its development! 10h. 31m. p.m., and about Sh. 53m. p.m. on the 30th; after which he is visible all night long. He souths on the 1st at 6h. 51m. a.m. and on the last day of the month at 5h. 8m. a.m. He still remains in Gemini.

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ASTRONOMICAL NOTES FOR SEPTEMBER. BY A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY. THE right ascension of the sun on September 1st, at Greenwich mean noon is 10h. 41m. 41-22s., and his declination north, 8^16′ 21-3"; he is consequently to the W. of the star x Leonis (map, Vol. X, p. 545). He is now approaching the equator; and at 9m. past 6 on the

night of the 26th satellite 1 will reappear from occultation at 10h. 27m. The shadow of satellite 2 will come on to Jupiter's disc at 10h. 46m., and pass off again at 1h. 20m. the next morning. Eight minutes afterwards satellite 2 itself will commence its transit and leave the face of the planet at 4h. 4m. This same moon will reappear from occultation at 11 o'clock on the night of the 28th. Finally, on the night of the 30th, satellite 3 will reappear from eclipse at 11h. 36m. 32s.; will be occulted at 2h. 35m. the next morning, and come out from behind the planet at 5h. 8m.; while 5m. later the shadow of satellite 1 will appear on the disc.

Saturn is still an evening star, but must be looked for early, as he sets between 10 and 11 at the beginning of the month, and between 8 and 9 at the end of it. He is on the meridian at 6h. 42m. in the evening of the 1st, and at 4h. 52m. in the afternoon

of the 30th. The time has practically past for favour-
He remains on the confines of
ably observing him.
Ophiuchus. Uranus is a morning star, rising about
6m. past 1 a.m. on the 1st, and about 11h. 10m.
on the last days of the month respectively. He comes
on to the meridian in broad daylight all through Sep-
tember, and can only be observed during the hour or
two which precede the morning twilight. He is
situated throughout September on the confines of
Gemini and Cancer. Neptune is not on the meridian
until 88m. past 2 on the night of the 1st, but
rises about 8 o'clock. He will be a little way to the
N.W. of μ Piscium during the entire month, his motion
being so exceedingly slow.

Shooting stars are rare in September. There is just a suspicion thongh of the existence of two periodical showers-one at the beginning of the month, the other in the interval between the 18th and the 25th.

LETTERS TO THE EDITOR.

[We do not hold ourselves responsible for the opinions of our correspondents. The EDITOR respectfully requests that all communications should be drawn up as briefly as possible.]

All communications should be addressed to the

EDITOR of the ENGLISH MECHANIC, 31, Tavistockstreet, Covent Garden, W.C.

All Cheques and Post Office Orders to be made payable to J. PASSMORE EDWARDS.

"I would have every one write what he knows, and this only, but in all other subjects: For such a person as much as he knows, but no more; and that not in may have some particular knowledge and experience of the nature of such a person or such a fountain, that as to other things, knows no more than what everybody does, and yet to keep a clutter with this little pittance of his, will undertake to write the whole body of physicks: a vice from whence great inconveniences derive their original."—Montaigne's Essays.

In order to facilitate reference, correspondents when speaking of any Letter previously inserted will oblige by mentioning the number of the Letter, as

well as the page on which it appears.

I hope I have been successful in explaining a
great difficulty, and that my listeners now see the
reason why I and my relatives come to the surface.
It is because the rocks which overlay me at my The visible phenomena of his satellites during the
birth have since been stripped off and slowly re- month of September will be as follows. On the 1st
moved by atmospheric agencies. All the formations day of the month, the first satellite will be eclipsed at
which were then piled above me, are to be found in 12h. 18m. 22s. The shadow of the second will pass on to
stratified rocks of later date; therefore, the period Jupiter's disc at 48m. past 1 in the early morning of
of my birth is not limited to any particular geological the 2nd; the first reappear from behind the planet's
epoch. I am found at the surface, surrounded by body at 3h. 49m., and the shadow of the second will pass
rocks of every age, even including those of the off Jupiter's limb at 4h. 20m.; 8m. afterwards this
Tertiary. Wherever the pent-up force of the earth's second satellite will commence its own transit. This, as
interior has thrust us up, there have we slowly ele-referable to the relative position of the Sun, Earth,
most of the readers of this column are aware, is
vated the rocks lying upon us. In many cases this
and Jupiter: in fact, on the 18th of this month, just
elevation has been so slow that it has hardly ex-371a. before noon, Jupiter will be in quadrature with
ceeded the rapidity with which these overlying rocks the Sun; that is to say, a line drawn from Jupiter to
have been denuded away! Think of the vast the Sun will form a right angle with one drawn to the
antiquity of our earth's crust, as indicated by these sun from the earth. Any one who will make a diagram
facts alone! Since the granites of the Highlands of this upon a piece of paper, will see how very
of Scotland were formed, twelve miles of over- obliquely the shadows of Jupiter's satellites will fall upon
lying material must have been removed! Where his disc relatively to our line of sight, and hence how
has it all gone to?
Ask the nineteen miles in it is that their shadows may traverse the whole width
vertical thickness of the known stratified rocks, of that disc before the moons which cast them come on
all of which have probably been formed since to it at all. On the night of the 2nd, at 11h. 46m., the
the granite itself. We scarcely need be afraid egress of the shadow of satellite 1 will take place. The
of Time, when we have Eternity to draw upon! satellite itself will not pass off the disc until 5m. past
Science Gossip.
1 the next morning. At 1h. 51m. in the early morning of
the 4th, the second satellite will reappear from occulta-
tion. On the night of the 5th, at 46m. after midnight, the
third satellite will begin to transit Jupiter's disc, and
will pass off afterwards at 3h. 12m. On the early
morning of the 9th the first satellite will be eclipsed at
2h. 11m. 45s., and the shadow of the second come on
to the planet's limb at 4h. 22m. On the 9th the in-
11h. 26m.; the satellite will come on an hour and
gress of the shadow of satellite 1 will take place at
twenty minutes later. The shadow will pass off at
1h. 40m. a.m. on the 10th, and the moon itself at 1m.
eclipsed at 11h. 12m. 23s., and satellite 1 reappear
On the night of the 10th satellite 2 will be
past 3.
from occultation at 13m. after midnight. The second
satellite will reappear from eclipse at 1h. 41m. 27s.
a.m. on the 11th, only to be occulted by the body of
the planet at 1h. 54m. It will reappear from this
occultation at half past 4. On the 12th the ingress
and its egress at 48m. past 1 in the next morning. An
of the shadow of satellite 3 will occur at 11h. 25m.,
eclipse of the first satellite will take place at
4h. 5m. 8s. a.m. on the 16th of the month. At
1h. 20m. a.m., on the 17th, the ingress of the shadow of
its shadow at 2h. 40m.
the same satellite will take place, the satellite following
The shadow will pass off at
3h. 84m. Satellite 2 will be eclipsed at 1h. 49m. 3s.
a.m. on the 18th, and the first reappear from occulta-
tion at 6m. past 2; the second will reappear from
its eclipse at 4h. 18m. 29s., and be occulted by
the planet at 4h. 32m. a.m. At 11h. 24m., on the
night of the same day, the first satellite will pass off
Jupiter's disc. On the night of the 19th, the egress of
the shadow of satellite 2 will occur at 10h. 46m.;
the moon casting it will come on 10m. after-
wards, and pass off at 1h. 33m. the next morning. The
ingress of the shadow of satellite 3 will take place
at 3h. 25m. Satellite 3 will be occulted at 10h.
42m. on the 23rd, and reappear from occultation at
1h. 10m. the next morning. The ingress of the shadow
of satellite 1 will take place at 3h. 14m. a.m. on the
24th, and the moon itself follow it at 4h. 34m. At
26m. 52s. past midnight on the 24th, the first satellite
will disappear in eclipse, and afterwards reappear from
occultation at 3h. 59m. a.m. on the 25th; the second
satellite will be eclipsed at 4h. 25m. 38s. At 11h. 2m.
at night, on the same day, the first satellite will begin
to transit Jupiter; its shadow will pass off at
54m. later, the satellite itself leaving the planet's
limb at 17m. past 1 the next morning. On the

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morning of the 23rd, crosses it; when autumn com-
mences. This is, of course, the period of one of the
equinoxes, so called from the approximate equality in
length of the day and night. The nearest approach to
such equality will, however, occur on the 25th, when the
day will be about 12h. 1m. long; and the length of the
night obviously 11h. 59m. The equation of time to be
subtracted from that indicated by any instrument con-
structed to show the sun's meridian passage, is on the
1st day of the month, Om. 6'1s., and on the last
day, 9m. 59'46s.

The moon enters her first quarter at 58m. past 1 in
the afternoon of the 2nd; is full about 12m. past 10 on
the night of the 9th; enters her last quarter at past
1 a.m. on the 18th; and is new at Ch. 34m. a.m. on the
25th. At noon on the 1st she is 5'6 days old; at the
same hour on the 2nd, 6-6 days old; and so on. On
the afternoon of the 6th, at 3 o'clock, libration will
bring an additional portion of her S.W. surface into
view, and the same cause will operate in rendering
more of her S.E. region visible at 1 o'clock in the
morning of the 21st. She will be in conjunction with
Saturn at 10h. 43m. a.m. on the 3rd; with Jupiter at
9m. past 2 in the early morning of the 18th; with
Uranus at 53m. after noon on the 20th; with Mars at
10h. 36m. the next morning; with Venus at 7h. 13m.
in the evening of the 23rd; with Mercury at 3h. 11m.
a.m. on the 26th; and finally, with Saturn again at
12m. past 6 in the evening of the 30th. She will have
occulted him (as will be mentioned immediately) 8m.
previously. Three fixed stars and-as we have just said-
Saturn will be occulted this month. Firstly, B.A.C.
6448 will disappear at the moon's dark limb at 8h. 7m.
on the night of the 4th, and reappear at her bright

THE HERSCHELIAN TELESCOPE. [289] SIR,-In my reply to Mr. White there is an error. A picture in Nichol's "Cyclopædia of the Physical adopted by Herschel. In this picture the axis of the Sciences," deceived me as to the arrangement actually eye-piece is not directed as it should be to the centre of the speculum, but parallel to the axis of the tube. This is the arrangement corresponding to the theoretically just way of making a Herschelian telescope, the vertex of the paraboloidal surface to which the to the eye-piece. Herschel in reality only tilted his mirror belongs falling on the edge of the mirror nearest mirror, an arrangement obviously imperfect. But he did not tilt it so that its optical axis passed through the centre of the eye-piece, as in Mr. White's arrangement. Had he done so, he would have had no field of view. He so tilted the mirror that its optical axis had a posi tion mid-way between the axis of the tube and the axis of the eye-piece (regarded as an indefinitely long straight line). In this way the image formed by the mirror was formed by oblique pencils. RICHARD A. PROCTOR.

MR. FIRTH AND "F.R.A.S." [290] SIR,-I really think that it is too bad of Mr. Firth to continue his absurd comments on the valuable Astronomical Notes by "F.R.A.S." All the readers of the ENGLISH MECHANIC owe a debt of gratitude to "F.R.A.S." for the preparation of these most useful notes. But we cannot expect him to contribute so much of his time for our advantage if his labours are to be continually carped at by some who seem unable to appreciate their value.

Mr. Firth's last letter reminds me of an episode in "David Copperfield." Mr. Dick has been installed into apartments somewhat limited in extent, but sufficient for his requirements; Mrs. Crupp, however, remarks that "there's not room to swing a cat," to which Mr Dick makes the apt rejoinder, that "he doesn't want

to swing a cat, so what can that matter to him?" We have been supplied by "F.R.A.S." with information true for the present time, but not for all time. Mr. Firth, however, remarks that thousands of years hence the state of the case will be different; may not we readers of the ENGLISH MECHANIC rejoin (not inaptly) that "we don't want to know what will happen thousands of years hence, so what can that matter to us ?"

The fact is that when the Nautical Almanac says that a celestial object at a given date and hour will have a certain longitude and latitude, it in effect asserts, as "F.R.A.S." has said, that that object will be in a certain part of such and such a constellation, the date and the hour are as truly parts of the statement as the longitude and the latitude. If it were not so, Mr. Firth would not be justified in rudely telling "F.R.A.S." that he is talking nonsense, because it would at least be obvious that "F.R.A.S." had been trying to render us a service, and therefore that any error he might unwittingly have made could not be too courteously and kindly corrected. But as a matter of fact "F.R.A.S." was wholly in the right.

Mr. Firth should endeavour to understand that men of "F.R.A.S.'s" calibre do not write in our columns to raise discussion, nor because of any pleasure it gives them to see their views in print (those who so write cannot be too severely handled): "F.R.A.S." writes, we all feel, from a disinterested desire to impart useful information. Nothing is more likely to discourage him in his exertions than to see his communications made a reason for twaddling comments by those who cannot appreciate the spirit in which he writes.

"F.R.A.S." has suggested that Mr. Firth had better do the astronomical notes himself. We are all interested in loudly protesting against any such arrangement. But I have a proposal to make which will no doubt suit all parties. Let Mr. Firth devote his energies to describing the state of the heavens 10,000 years hence; and let him give directions that his papers shall be reserved until the epoch they refer to.

RICHARD A. PROCTOR.

THE NATURE AND CAUSE OF LIGHT. [291] SIR,-I am sorry to see that "T. A." has not taken in good part my suggestion that his views about light are unsound. I did not make that suggestion without a purpose. Those who "confuse counsel by words without knowledge" must not complain if they meet with a check. "T. A." should remember how large a proportion of our readers trust only to these who know to save them from being misled and confused by those who do not know. In saying this I am not claiming anything on my own account; I have not found out for myself what I know about light, but have learned it from the careful study of the work (the observations, experiments, writings, and so on) of other men; and I knew that most of "T. A.'s" views were opposed altogether to the whole series of results obtained by the scientific students of the subject he treated of. I held it to be important that the readers of our journal should also know this; and therefore, without any ill-feeling at all towards " T. A.," I said

as much.

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Let me add that he had been very blunt himself in contradicting me about the "crepuscular curve,' whose existence he abruptly denied. It turned out that he was simply unfamiliar with the meaning of that well-known expression. But I may take this opportunity of admitting the justice of his subsequent criticism. Since the words "twilight curve" express exactly the same as "crepuscular curve," and are much less likely to be misunderstood, I ought to have used them. I make a rule of using the simplest words I can find; but in this case, by inadvertence used the less familiar expression.

17.6

MONCRIEFF'S HYDRO-PNEUMATIC GUN-CARRIAGE.

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MOUNTING INSECTS FOR THE MICROSCOPE.

[293] SIR,-Allow me to recommend #Q. Sea" to catch every insect that comes in his way, to eat the same to his death-bottle, and to afterwards The fact is, "a list of objects easily obtained occupy two or three numbers of our MECHINE, space which I think would hardly be allowed, ena ti so discerning a body as the microscopists.

Perhaps "Q. Sea" would say that such a proce would doubtless give him a large supply of subjec mounting, but how about the names of the i caught? These can easily be learnt by means d book on entomology; and, indeed, not only the but also the various organs, &c., by which the ch which the insects under examination belong i tinguished; and thus the operator knows whethe look for a gizzard, or a padded, or a hooked foot or not. And, last but not least, a considerable as of scientific knowledge of entomology is gained.

Concerning the mode of mounting (I say " because I have as yet spoken only of insects, and of these as should be mounted by the mode unde cussion would be quite enough to fully occupy the of a beginner for some time to come; and there prefer classifying objects according to their mos preparation, not necessarily of mounting and treat of them separately), the following I find very effi both for very large whole insects, and for min sects, or only parts of them.

[292] SIR, I send you a drawing, taken from Engineering, showing Captain Moncrieff's improved gun carriage in all its details, and indicating both the loading and firing position of the gun, which is mounted upon a revolving carriage. The circular travel described by the wheels upon the lower deck is Now as to the first question "T. A." asks, I must re- 12ft. 9in., and at the upper deck the framework is mind him that it belongs rather to the subject of che-free to turn round an inclined path 17ft. 6in. diameter, mistry than of light considered in the abstract. But upon which rollers set at an angle take their bearing, apart from this, we do not yet know why light from the the revolving motion being effected by bevel gearing, as violet end of the spectrum should have the power of shown. Under the carriage is placed an hydraulic producing chemical action (of causing the combination cylinder, the ram of which has a T-shaped head, and or decomposition of certain substances), while light is provided with small rollers which bear upon the The insect having been caught, is introduced in from the red end has no such power. How, or why, under side of the moving part of the carriage. In the "death-bottle" (the modus operandi of which was g then, should I be expected to explain a well-known but lower part of the carriage, that which has no move in a previous number), and when dead is diss still more recondite phenomenon? "T. A." might ment except a circular one, a vertical opening is left according to what parts are wished to be presen as reasonably say, "Mr. Proctor professes to have some one each side, as shown, and these serve as guides for and then put into a rather weak solution of ass knowledge of the laws of light and colour, let him tell the ascending or descending ram, the end of the T-potash, made by adding to the liquor potasse d me, then, why some people have red hair, others black, head, projecting through the openings on either side. chemist about its own bulk of water. In this solai and yet others brown or flaxen." "T. A." some time Parallel links, the position of which, when the gun is in the future object must be allowed to remain t back called on me and on our "F.R.A.S." par excellence, firing position, is vertical, are secured at the lower end fortnight to three months, according to the textu to answer two questions of similar profundity. He was to the bottom of the fixed part of the carriage, and at size of subject. When the object has been consi invited to reflect on an old proverb about questions and the upper end to the movable part, their motion being to have remained long enough in the caustic (and answers as related to wisdom and folly. Truly, with- the same as the links in a parallel ruler, as the gun this point a little consideration will be quite suffe out reflecting on "T. A.'s" wisdom in asking this parti- rises or falls. Connected with the hydraulic cylinder guide, and, indeed, it does not matter if an object cular question, I must admit that I should be but foolish is a pipe leading to an air vessel, and having a valve left a matter of two or three days beyond the necessar did I pretend to answer it. That it will be answered chamber containing a spherical valve. A bye-pass time, more especially if to this solution of potash some day I make no question, but years of patient la- pipe, which can be opened or closed by a lever from about one half its bulk of methylated spirit be added bour must I believe come first. At present let us con- the gun platform, establishes an independent communi- it should be taken out and thrown into water (as pare tent ourselves with stating what the experiment shows. cation between the air chamber and that portion of the as possible) and allowed to remain there for four-andFirst of all, light, passing through an orange-yellow main pipe between the valve chamber and the hydrau- twenty hours, the water being changed at least one glass will not affect a sensitized collodion plate. That lic cylinder. In the rear of the air chamber is a small during this period. Taken out of the water, the objec was to be expected, because little or no light from the pipe for supplying water deficiencies by leakage. The must be brushed clean with a camel's-hair brush and violet end of the spectrum can pass through such glass action of the mechanism is as follows:-Water is a plentiful supply of clean water; it is then arranged (as we know from the absorption spectra of orange- pumped into the apparatus until the air in the air on a glass slide according to taste; another slide is pat yellow glasses). Light waves of more than a certain chamber is placed under a considerable pressure. on the top, and the whole squeezed firmly between a length cannot produce the required chemical action, When the gun is loaded, and it is desired to raise it, strong-springed American clothes-peg, or a letter-claw, then, it appears. But after the collodion film has been the opening of the bye-pass establishes a communica- and in this position is allowed to dry for a few days or subjected to the action of actinic light, orange-yellow tion with the hydraulic cylinder, the ram of which a week, according to texture, size, &c., of object. When light has the power of destroying the impression and rises carrying with it the gun. The valve is then dry, the object is carefully removed from the slide, and fogging the plate all over. A most interesting fact, closed, and when the piece is fired the recoil throws it immersed in strong methylated spirit, to extract the serving to show that after the arrangement of the mole- back with a constantly decreasing velocity, due partly last trace of moisture, and there left for a period cules of the film has been affected in a certain way, by to the increasing resistance of the coupling links and varying according to circumstances. From the spirit the shorter actinic waves, the longer light waves have partly to the increasing pressure within the air the object should go into ether (methylated will do) the power of further influencing the arrangement of chamber КАРРА. and should be left there for three or four days. At the

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