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diminished tbeir consumption of imported commodities*. The increase of £478,681, as shown above, has, therefore, overstocked onr markets. Tin articles which chiefly make np this increase are all subject to the new duties imposed by the present tariff, and the increase of £447,109 which the figures exhibit must be very bewildering and disappointing to those politicians who imposed the duties for the purpose of restricting importations and encouraging local industries. With reference to onr export trade, it appears that contemporaneously with the increase in imports there was a considerable diminution in the value of exports. The decline of wool last year was somewhat compensated for by a material increase in uthor products of our pAstoral industry—viz., tallow, skins, leather, bonedust, and preserved meats, the last-named article contributing i'SO,835 to the value of exports, as compared with £28,565 the previous year."

Addenda III. (From the Times.) The following extract, relating to the state of the labour-market, is from the Argut of April 33rd. It disposes of the foolish and selfish " mechanic cry " raised from tune to time here against the continuance of assisted immigration:—

The Labour Market. "Tho long-continued drought baring now fairly broken up, farming operations have beou resumed with great activity throughout the country, and there has been a corresponding demand created'for farm labourer-. All descriptions of tradesmen are able to obtain full work at tho current rate of wages. In many parts of the country tho rates rule higher than those quoted. On one Government contract tho bricklayers employed were receiving 12s. per day, and an attempt was made to extort 14s. per day by means of a strike. For domestic servants tho demand is as great and as badjv supplied as ever. Since last mail, the immigrant ship Trrrg has arrived with 366 passengers; but, owing to sickness on board, the vessel has been detained at the quarantine ground. As most of these passengers will go to their Wends, tho market will be but jjightly relieved."

Addenda IV. The reform agitation is still fresh in onr memories, and agitations are still in progress relating to education and other matters. Would dt not be advisable to "agitate" that the Government supply information, more especially adapted to the wants of immigrants, relating to every •' colony" under British rule. This information could be supplied in pamphlet form at a remunerative price of (say) Cd.

MEDICAL EXPERIMENT.

ON Monday, July 4th, n large gathering of the medical profession, numbering very nearly '2,000, and embracing the ilitt of the metropolitan and surburban practitioners and some distinguished foreign visitors, assembled at the invitation of one of their fraternity, at the Royal Polytechnic Institution, to witness the trial of anewmode of conveying practical instruction in a department of surgery which has long been considered as one of the opprnliria vuxticinw. For some time past efforts have been inude to improve in various ways the means of imparting clinical information, as distiiiguished from mere book-knowledge, to the students of medicine in this country. The University of London has of late taken the lead amongst examining bodies, by requiring of its graduates in medicine tLi;it they should pass a practical examination, in addition to the previous theoretical examination, in order to obtain its much-coveted degrees; and tho 'ate Sir James Clark was a steadfast advocate of 'he necessity of improvement iu this most important branch of medical education. Tho large theatre and effective optical apparatus of tho Institution having been placed for this purpose by the directors at the disposal of the profession, i)r. Bahnanuo Squire proceeded to demonstrate to his audience some of the more important cases of cutaneous disease that had lately occurred iu the practice of the British Hospital for Diseases of the Skin hi Great Marlborough-street, ami also in Finsbnrysquaro, of which institution Dr. Squire is one of the honorary sturgeons. The room having been darkened, magnified images of the patients themselves were thrown, considerably larger than life-size, on the spacious screen of the theatre, by means of the dissolving-view apparatus, so that all the details of the various eruptions were plainly visible even from the most distant parts of the theatre. Dr. Balinauno Squire, after given a rtmime of the acknowledged difficulties of imparting a practical knowledge of the medical art to stadents, proceeded to show how the method he submitted would dispose at least of the more serious of these difficulties, and explained that it was not only applicable to the department of practice that he himself followed, but was capable of wide extension to the subject of medical education generally. Students of medicine at every hospital persisted hi docking round the most popular teacher; consequently, but a few could get anything like a satisfactory view of the patient concerning whose case instruction was being given. Again, it was by no means an easy thing, even at our largest hospitals, to find wit'du a limited space of time a sufficient variety of illustrative cases to enable the members of any given class to go forth from the hospital with a comprehensive practical knowledge of the subject treated. The plau he proposed wonld, by magnifying the object to be demonstrated, enable every detail to be seen by every member of a large class, and to be pointed out to

all of them by the lecturer at the time he was describing it. By the method proposed, the patient might be instantaneously photographed before either the natural progress of his disease or its amelioration under the resources of art had impaired its utility as a means of conveying instruction; and at the same time in cases where colour formed an important feature of it, this could be added to the photograph itself by an expert artist, working tinder the eye of the teacher himself. In the case of cutaneous disease—the most difficult of all subjects to illustrate bytbese means—colour was certainly a most important feature. But he appealed to those he saw around hini, many of whom he knew to be well versed in this special subject, whether the illustrations he had brought before them were not in colour as well as in form and shadow sufficiently life-like to afford a lecturer ample opportunity for pointing out to a class of students all the essential peculiarities of each disease, and to enable thosestudentswhen they entered upon private practice to recognize at once the nature of similar cases whenever they might meet with them. He trusted to see at the next medical session this important aid to tuition, as he would take leave to call it, utilized at all of our great medical schools, not only in the matter of cutaneous diseases, which might be taken as a crowning test of its efficacy, but also in the matter of tumours, dislocations, deformities, fractures, characteristic alterations of the countenance, and in short, all occasions to winch this process is applicable.

WHAT IS ENERGY ?•
In Two Parts.Pakt H.

IN our first article it was shown that energy, or the power of doingwork, is of two kinds—namely, energy due to actual motion, and that due to position. We ended by supposing that a stone shot vertically upwards had been caught at the summit of its flight and lodged on the top of a house; and this gave rise to the question, What has become of the energy of the stone'! To answer this we must learn to regard energy, not ns a analili/, but rather as a thing.

The chemist has always taught ns to regard quantity or mass of matter as unchangeable, so that amid the many bewildering transformations of form and quality which take place in the chemical world, we can always consult our balance with a certainty that it will not play us false. But now the physical philosopher steps hi and tells us that energy is quite as unchangeable as mass, and that the conservation of both is equally complete. There is, however, this difference between the two tilings—the same particle of matter will always retains the same mass, but it will not always retain the same energy. As a whole, energy is invariable, but it is always shifting about from particle to particle, and it is hence more difficult to grasp the conception of an invariability of energy than of an invariability of mass. For instance, the mass of our luminary always remains the same, but its energy is always getting less.

And now to return to our question,—What has become of the energy of the stone'! Has this disappeared? Far from it; the energy with which the stone begun its flight has no more disappeared from the universe of energy, than the coal, when we have burned it in our fire, disappears from the universe of matter. But this has taken place:—the energy has changed its form and become spent, or has disappeared as energy of actual motion, in gaining for the stone a position of advantage with regard to the force of gravity.

If we study this particular instance more niinntely, we shall see that during the upward flight of the stone its energy of actual motion becomes gradually changed into energy of position, while the reverse will take place during its downward flight if we now suppose it dislodged from the top of the house. Li this latter case the energy of position with which it begins its downward flight is gradually reconverted into energy of actual motion, until at last, when the stone reaches the ground, it has the same amount of velocity, anil therefore of actual energy, which it hod at first.

Let us now revert for a moment to the definition of energy, which means the power of doing work, and we shall see at once bow we may gauge numerically the quantity of energy which the stone possesses ; and in order to simplify matters, let us suppose that this stone weighs exactly one pound. If therefore, it has velocity enough to carry it up one foot, it may be said to hare energy enough to do one unit of work, inasmuch as we have defined one pound raised one foot high to be one unit of work; and in like manner if it has velocity sthBcient to carry it 16ft. high, it may be said to have an energy equivalent to 16 units of work or foot-pounds, as those units are sometimes called. Now, if the stone be discharged upwards with an initial velocity of 32ft. per second, it will rise to ltift. high, and it has therefore an energy represented by 16. But if its initial velocity be 64ft. per second it will rise 04ft. high before it turns, and will therefore have

By Balvour Stewart, in Nature.

energy represented by 64. Hence we see that liy doubling the velocity the energy is qnadrriple-d. siut we might show that by tripling the velocity tht energy is increased nine times. This is exprvss«>j in general terms by saying that the energy <.c quantity of work which a moving body can acton.plish varies as the square of its velocity. This, fact is well known to artillerymen, for a ball wit h a double velocity will penetrate much more thm twice as far into an obstacle opposing its progrei**.

Let ns now take the stone or pound weight., bar ing an initial velocity of 64ft. per second, urul cocsider the state of things at the precise moment wki it is 48ft. high. It will at that moment have as actual velocity of 32ft. per second, which, as ** have seen, will represent i6 units of work. lint c started from the ground with 64 units of work in it What, therefore, has become of the difference—<? 48 units? Evidently it has disappeared as acta,' energy; but the stone, being 18ft. high, has * energy of position represented by 48 units; so tii at this precise moment of its flight its actual energy |16J plus its energy of position (481, are together equal to the whole energy with which it startMi (04).

Here, then, we have no annihilation, of energy, but merely the transformation of it from actnaj energy into that implied by position; nor have we any creation of energy when the stone is on it* downward flight, but merely the rv-transforraatk-u of the energy of position into the original fonn of actual energy.

We shall presently discuss what becomes of this actual energy after the stone has struck the ground, but hi the meantime we would repeat our remark how intimate is the analogy between the piivjDx-aJ and the social world. In both cases we have actual energy and energy of position, the only difference being tliat in the social world it is impossible in measure energy with exactness, while in the mechanical world we can gauge it with the utmost precision.

Proteus-like, this element energy is always changing its form; and hence arises the extreme difficulty of the subject; for we cannot easily retain a sufficient grasp of the ever-changing element to argue experimentally regarding it. All the varieties of physical energy may, however, be embraced under the two heads already mentioned, namely, energy of actual motion and ot position. We havo chosen the force of gravity, acting uy»n a stone shot up into the air, as our example; but there are other forces besides gravity. Thus, a watch newly wound up is in a condition of visible advantage with respect to the force of the main-spring; and as it continues to go it gradually loses this energy of position, converting it into energy of motion. A crossbow bent is likewise in a position of advantage with respect to the spring of the bow; and when its bolt is ilischarged, this energy of position is converted into that of motion. Thus aguin, a meteor, a railway train, a mouutoin torrent, the wind, all represent energy of actual visible motion; while a head of w-ater may be classed along with a stone at the top of a house as representing energy of positiouThe list wliich represents visible energy of motion and of position might lie extended indefinitely,- but we must remember that there are also invisible molecular motions, which do not the less exist because they are invisible.

One of the best known of these molecular-cnergies is radiant light and teat—a species which can traverse space with the enormous velocity of 160,OAM1 miles u second.

Although itself eminently silent and gentle, iu its action, it is nevertheless the parent of mosi-of the work which is done- in the world, as we shall presently see when we proceed to another divisiou of our subject. In the mean time we may state that radiant light and heat are supposed to consist of a certain uudulatory motion traversing an ethereal medium which pervades all space.

Now, when this radiant energy fulls upon a substance, part of it is absorbed, andin the process- of absorption is converted into urtlinary Imat. The oudulutory motion which had previously tru«cr»I the thin ether of space has now become linked with gross palpable mutter, and uwaiifests itself iu & motion which it produces ill the particles of thht matter. The violence of this rotatory or vortex-like motion will thus form a measure of the heat which the matter contains.

Another species of molecular energy consists of electricity in motion. When an electric current is moving along a wire, we have therein the progress of a power moving like light with 'incvriuous velocity, and, like light, silent in its operation. Silcut,.we say, if it meets with no resistance, but exceedingly formidable if it be opposed; for the awe-inspiring flash is not so much the eloctricityitself as the visible punishment which it has infnetod on the air for daring to impede its progress. Had there beau a set of stout wires between the thunder-cloud and tue earth, the fluid would hnv* passed into the ground, without disturbance.

The molecular energies which we have now described may be imagined to represent motion of some sort not perceived by the oiitward.eye, but present nevertheless to the eve of the understanding; they may th«refore be compared to th-uuiifctgy of a budy in. visible motion, or actual eiiergy, as we have termed it.

But we have also molecular energies which are more analogous to the energy of position of a stone at the top of a cliff.

For instance, two bodies near one another may I»e endowed with a species of energy of position itae to opposite electrical slates, in which case they have a tendency to rash together, just as a stone at the tori of a cliff has a tendency to rush to the earth. If the two bodies be allowed to rush together, this «wergy of position will be converted into that of ■visible motion, just as when the stone is allowed to «a\rop from the cliff, its energy of position is concerted into that of visible motion.

There is finally a species of molecular energy caused by chemical separation. When we carry a tstoue to the top of a cliff, we violently separate two bodies that attract one another, and these two bodies are the earth and the stone. In like manner when we decompose carbonic acid gas into its constituents we violently separate two bodies that attract one another, and these are carbon and oxygeu. When, therefore, we have obtained in a Be-parate state two bodies, the atoms of which are prepared to rush together and combine with one another, we have at the same time obtained a kind of energy of molecular position analogous on the small scale to the energy of a stone resting upon the top of a house, or on the edge of u cliff ou the 'large or cosmical scale.

MOTIVE POWER FROM DEEP WELLS.

THE value of the hydraulic ram for raising w»tcr to the top ef country mansions, by utilizing the power of a neighbouring stream, has already been proved by experience; but to raise water from wells, the pfflap has hitherto been considered the most convenient apparatus. But if the invention of Mr. Hanreau, of Meaux, France, succeed according to his anticipations, pumps will no longer be necessary. Take a case in which it is proposed to raise a certain height the water of a spring or stream rising in an ordinary well. This well is extended to the necessary depth for affording a fall below the level of the spring or stream sufficient for actuating u hydraulic ram placed a short distance from the bottom of the well. At the bottom of the well a bori ng is effected until the absorbent bed is reached. The characteristic feature of this arrangement consists in intercepting the water of the spring or stream by means of an annular trough communicating with a reservoir, from which the water descends into the hydraulic ram through a conduit. One portion of the water escapes through the valve of the ram and flows away through the tubing into the bed which absorbs it. The other portion is raised by the action of the ram through the pipe into a reservoir, where it is employed for any desired purpose. The opening of the tubing is covered by a grating for preventing the entrance of foreign matter, which might eventually choke the tnbicg, and also destroy tiio absorbent properties of the feed. If the yield -of water in the well is too small, a second rcserveir may be connected to the .first by means of a siphon with intermittent action.

THE LEAF AS A 'WORKER.

T\R. J. S. SEW ALL, in the American Entomolo-L' gist nnd Botanist, says, f.et us consider the leaf as a worker. Let us lean* irhat it decs, ami Jww it does it. In the first place, let us fully understand what we moan by wortir—or let us agree as to the definition ef the term. To illustrate, we sny of the locomotive, that it performs a certain amount of labour, it turns so many wheels, drives so many looms, draws so many cars so many miles an hour— we speak of it as a worker. So, too, of man—we speak of him as a worker. He performs so much labour, physical or ineutfJ. Yet the locomotive, with all its penderous bars, its mysterieas valves, its great levers, its hidden springs, can do nothing. It is dead, inert metal. True, too, of man—that wouderful combination of bones and muscles and nerves and tissues can do nothing, but decay, and be resolved to dust again. The brain cannot think, the eye cannot see, the ear cannot hear, the nerves cannot thrill, the muscle cannot contract.

Ill the some sense the leaf can do nething. Yet in the same sense thi.t a locomotive can draw a train, ortbat man canSshink and labour, is the leaf a labourer .that outworks them alL The locomotive is a combination of material things st- arranged that through or by them we discover the operations of force. Man himself ds nothing more. The leaf is the same. Better, j-erhaps, that *c say that these aretheieorkshop wherein force exhibits itself, and produces results. When did the leaf begin its work? It was the first to rise on creation's morn and g» forth to labour. Ere the almost shoreless ocean dashed upon the low Silurian plain, theleaf was atiits work. And through all the long ages it has worked—worked to develop I ettcr and higher forms of life. And the earth's bread face is written all over with the erndences of its faithfulness. Xew -what doe* a do? It jumps water iron

the ground, through the thousands of tubes in the stem of the tree (the tubes which itself has made), and sends it into the atmosphere in the form of unseen mist, to be condensed and fall in showers— the very water that, were it not for the leaf, would sink in the earth, and find its way perchance through subterranean channels to the sea. And thus it is that we see it works to give us the " early and the latter rain." It works to send the rills and streams, like lines of silver, adown the mountain and across the plain. It works to pour down the larger brooks which turn the wheel that energizes machinery, which gives employment to millions. And thus a thousand wants are supplied—commerce stimulated—wealth accumulated—and intelligence disseminated through the agency of this wealth. The leaf does it all.

It has been demonstrated that every square inch of leaf lifts three flve-hundredths of an ounce every twenty-four hours. Now, a large forest tree has about five acres of foliage, or six million two hundred and seventy-two thousand six hundred and forty square inches. This being multiplied by three five-hundredths (the amount pumped by every inch) gives us the result—two thousand three hundred and fifty-two ounces, or one thousand one humlrod and seventy-six quarts, or two hundred and ninetyfour gallons, or eight barrels. A medium sized forest tree, about five barrels. The trees on an acre give eight hundred barrels in twenty-four hours. An acre of grass, or clover, or grain, would yield about the same result.

The leaf is a worker, too, in another field of labour, where we seldom look—where it exlubibs its unselfishness—where it works for the good of man in a most wonderful manner. It carries immense quantities of electricity from the earth to the clouds, and from the clouds to the earth. Rather dangerous business transporting lightning. I think it would be considered contraband by the "U.S," or "Merchant's Union,' or any common carriers: but it is particularly fitted for this work. Did you ever see a leaf entire us to its edges? It is always pointed, and these.points, whether they he large or small, tire just fitted to handle this dangerous agent. These tiny fingers seize upon and carry it away with ease and wonderful despatch. There must bo no delay; it is "time freight." True, sometimes it gathers up more than the trunk can carry, and in the attempt to crowd nnd pack the baggage the trunk gets terribly shuttered, and we say that lightning struck the tree. But it had been struck a thousand times before. This time it was overworked.

As we rub a stick of sealing-wax or a glass tube with a warm silk handkerchief, so the air is always rubbing over the face of the earth with greater or less rapidity. And what a huge electrical machine I But be not afraid, the leaf will see that it is taken care of. As we guard our roofs from the destructive action of lightning—dashing to the earth— crashing, rending, burning on its way—by erecting the lightning rod, whose bristling points quietly drain the clouds, or failing to do this, receive the charge and bear it harmless to the earth—so God has made a living conductor in every pointed leaf, in every blade of grass. It is said that a common blade of grass, pointed by nature's exquisite workmanship, is three times as effectual as the finest cambric needle; and a single twig of leaves is far more efficient than the metallic point of the best constructed rod. What, then, must be the agency of a single ferest in disarming the forces of the storm of their terror. Nature furnishes the lightning, and it furnishes the lightning rods. Take a hint, then, and plant trees.

SHE HALFPENNY POSTAGE.

THE (bill for further regulation of duties of pestage, and for other purposes relating to the Poet-office, has just been published. For the purposes of the Act, the Channel Islands and the Isle of Man are to fee deemed parts of the United Kingdom. The Act will come in force on Oct. 1st. Alio* ance will be made for stamps to those who at that time may bu in possession of them. Any publication coming witliiu the following description shall, for the purposes of the Act, be deemed a newspaper—that is to say, any publication consisting wholly or in great part of political or other news, or of articles relating thereto, or to other current topics, with or without advertisements, subject to these conditions :—That it shall be published in the United Kingdom; that it shall be published in numbers at intervals of not more than seven days; that it be printed on a sheet or sheets unstitched; that it have the title and date of publication printed at the top of every page. The proprietor or printer of any newspaper may register it at the General Post-office in London, at such time in each year, and in s«ch form, and with such particulars! as the Postmaster-General from time to time direct s, paying on each registration such fee, not exeeeSing five shilKngs, as the PostmasterGeneral, with the approval of the Treasury, from time to time directs. On and after the 1st of October, 1*70. registered rewspapers, book packets, pattern or sample packets, and post cards, may be

sent by post in the United Kingdom at the following rates of postage :—On a registered newspaper, not exceeding, with any supplement, and with any cover, six ounces in weight, one halfpenny. On a book packet, or pattern or sample packet, if not exceeding two ounces in weight, one halfpenny; if exceeding two ounces in weight, for every additional two ounces, or fractional part of two ounces, one halfpenny. On a post cold, one halfpenny. The Treasury may, from time to time, by Treasury warrant, allow any newspapers and periodical publications, British, Colonial, and foreign, to be sent between the United Kingdom and places out of the United Kingdom, whether through the United Kingdom or not, nt such rates of postage not exceeding twopence for each newspaper or publication, irrespectively of any colonial or foreign postage, and on such conditions as they think tit, and according to Post-office regulations to be from timeto time made in that behalf.

CARMINE.

THIS beautiful red pigment is obtained from the cochineal insects, which were natives of Mexico originally, but are now raised with success in many other countries, and particularly in India, Spain, and Algeria. They feed upon the Nopal cactus or prickly pear, on which the females fix themselves, being wingless, and from which they never move. At a certain time in the year they ore gathered from the pear by means of a brush, and they are then plunged in hot water and exposed in the sun to dry. When dried they have the appearance of small berries or seeds, being of a grayish purple colour, and in this state they form the cochineal of commerce, and are exported to this and other countries for making carmine. It takes 70,000 of the dried cochineals to weigh a pound.

Carmiue is tho most brilliant of all red colours, but its beauty depends materially upon the method of manufacturing. It was first prepared by a Franciscan monk at Pisa, who discovered it accidentally while compounding medicines containing cochineal, and in 1656 it began to be manufactured. A great many experiments have been made to extract it in a state of absolute purity, but repeated trials have proved this to be a most delicate operation, and one requiring great skill, as well as very carefnl attention.

There are several modes of manufacturing it. One process is to digest lib. of cochineal in 3 gallons of water for fifteen minutes; then add 1 ounce of cream of tartar; heat gently for ten minutes; add half an ounce of alum; boil for two or three minutes; and, after allowing the impurities to settle, the clear liquid is placed in clean glass pans, when the carmine is slowly deposited. After a time the liquid is drained off, and the carmine, dried in the shade. Roret, in his well-known encyclopedia of colours, gives the following as all old method: —20 grammes (310 grams) of cochineal, 2 grammes of the seed of chouau, an Oriental tree, 10 grammes of the bark of the autonr, another Oriental tree, and 1 gramme of alum are pulverized, each hi a separate mortar. 2 litres (2J quarts) of veryclear river or rain water is inado boiling in a clean vessel. When it boils, the chouan is thrown into the vessel, and after boiling very fast the liquid is poured cautiously through tine white linen into another well cleansed vessel. This liquid is again made to boil, and when it commences boding the. cochineal is added: next autour, and nt last the alum, at which moment the vessel is taken away from the fire. The liquid is poured into a porcelain plate, and left there for seven or eight hours in order to subside. Then the clear liquid which flows uppermost is cautiously discharged, and the sediment is exposed to the sun to dry. When dried it is gathered from the plate with a fine brush or a feather, and this very fine and very beautifully coloured powder is the carmine of cochineal.

In the preparation of carmine, aiuch depends on a clear atmosphere and bright, sunny day, during the process, as the beautiful colour is in no case nearly so good when it is prepared in dull weather. This "accounts in a great part for the superiority of French carmine over that made in England. Moreover, carmine cannot be made during cold weather, because in such case it will not precipitate to the bottom of the liquid, but will form into a sort of jelly, and in this condition will soon spoil.

Pure carmine is very expensive, aud this has led to the manufacture and sale of many substitutes. All of them are inferior, however, and for finest work only the pure article should be employed.

THE SCHOOL OF MINES' SCHOLARSHIPS—At a meeting of the Council of the Roral School of'Mmes held on Saturdnv, .Tulv 2nd. the following awards were made :—Two Roval Scholarships of £\o each for llrst Year's students, to W. H. Greenwood and F. C. Mifoord; H.K.H. the Duke of Cornwall's Scholarship to V. C. GUlehrist; the Royal Scholarship of £25 to K. I.. Atkinson: the De la Beene Medal nnd prize of books to W. Gowlnnd; and the Director's Medal and prise of books to P. C. GUlehrist. The Edward Forbes Mclal and prize of books were not competed lot this year..

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MECHANICAL MOVEMENTS.

MECHANICAL MOVEMENTS.*
(Continuedfrom jKiyc 366.)

Q Afl Proportional compasses used in copying rC\JOt drawings on a given larger or smaller scale. The pivot of compasses is secured in a slide which is adjustable in the longitudinal slots of legs, and capable of being secured by a set screw. The dimensions are taken between one pair of points and transferred with the other pair, and thus enlarged or diminished in proportion to the relative <li*tances of the points from the pivot. A scale is provided on one or both legs to indicate the proportion.

210. Bisecting gauge. Of two parallel cheeks on the cross-bar one is fixed and the other ailjustable and held by thumb screw. In either cheek is centred one of two short bars of equal length, united by a pivot, having a sharp point for marking, 'libis point is always in a central position between the cheeks, whatever their distance apart, so that any parallel sided solid to which the cheeks are adjusted may be bisected from end to end by drawing the gauge along it. Solids not parallel sided may be bisected in like manner, by leaving one cjieek loose, but keeping it in contact with solid.

211. SoLf-rccording level for surveyors. Consists of a carriage, the shape of wliich is governed by an isosceles triangle having horizontal base. The circumference of each wheel equals the base of the triangle. A pendulum, when the instrument is on level ground, bisects the base, and when on an inclination gravitates to right or left from centre accordingly. A drum, rotated by gearing from one of the carriage wheels, carries sectionally ruled paper, upon which pencil on pendulum traces profile corresponding with that of ground travelled over. The drum can be shifted vertically to accord with any given scale, and horizontally, to avoid removal of filled paper.

212. Wheel-work in the base of capstan. Thus prpvided, the capstan can be used as n simple or compound machine, single or triple purchase. The drumhead and barrel rotate independently; the former, being fixed on spindle, turns it round, and when locked to barrel turns it also, forming single purchase ; but when unlocked, wheel-work acts, and drumhead and barrel rotate in opposite directions, and velocities as three to one.

213. J. W. Howlett's patent adjustable frictional gearing. The upper wheel, A, shown in section, is composed of a rubber disk with V-edge, clamped between two metal plates. By screwing up the nut, B, which holds the parts together, the rubber (Use is made to expand radially, and greater tractive power may be produced between the two wheels.

214. Scroll gear and sliding pinion, to produce an increasing velocity of scroll-plate, A, in one direction, and a decreasing velocity when the motion is reversed. Pinion B, moves on a feather on the shaft.

216. P. Dickson's patent device for converting an oscillating motion into intermittent circular, in either direction. Oscillating motion communicated

to lever, A, wliich is provided with two pawls, B and C, hinged to its upper side, near shaft of wheel, D. Small crank, E, on upper side of lever. A, is attached by cord to each of pawls, so that when pawl C is let into contact with interior of rim of wheel D it moves in one direction, and pawl B is out of gear. Motion of wheel D may be reversed by lifting pawl C which was in gear, and letting opposite one into gear by crank E.

216. A device for assisting the crank of a treadle motion over the dead-centres. The helical spring, A, has a tendency to move the crank, B, in direction at right-angles to dead-centres.

217. Continuous circular motion into a rectilinear reciprocating. The shaft, A, working in a fixed bearing, D, is bent on one end, and fitted to turn in a socket at the upper end of a rod, B, the lower end of which works in a socket in the slide, C. Dotted lines show the position of the rod, B, and slide, when the shaft has made half a revolution from the position shown in bold lines.

218. Buchanan nnd Righter's patent slide-valve motion. Vidvc A is attached to lower end of tod B, and free to slide horizontally on valve-seat. Upper end of rod B, is attached to a pin which slides in vertical slots; and a roller, C, attached to the said rod, slides in two suspended and vertically adjustable arcs, D. This arraugemeu t is intended to prevent the valve from being pressed with too great force against its seat by the.pressure of steam, and to relieve it of friction.

219. Continuous circular motion converted into a rocking motion. Used in self-rocking cradles. Wheel, A, revolves, and is connected to a wheel, B, of greater radius, which receives an oscillating motion; and wheel B is provided with two flexible bands, C, D, which connect each to a standard or post attached to the rocker, E, of the cradle.

220. Arrangement of hammer for striking bells. Spring below the hammer raises it out of contact with the bell after striking, and so prevents it from interfering with the vibration of the metal in the bell.

221. Trunk engine used for marine purposes. The piston has attached to it a trunk at the lower end of which the pitman is connected directly with the piston. The trunk works through a stufliug-box in cylinder-head. The effective area of the upper side of the piston is greatly reduced by the trunk. To equalise the power on both sides of piston, high-pressure steam has been first used on the upper side and afterwards exhausted into and used expansively in the part of cylinder below.

222. Oscillating piston engine. The profile of the cylinder A, is of the form of a sector. The piston, B, is attached to a rock-shaft, C, and steam is admitted to the cylinder to operate on one nnd the other side of piston alternately, by means of a slide-valve, D, substantially like that of an ordinary reciprocating engine. The rock-shaft is connected with a crank to produce rotary motion.

223. Boot's patent double-quadrant engine.

This is on the game principle as 222; bat two single-acting pistons. B, B, are used, nod both connected with one creak, D. The steam is admitted to act on the outei sides of the two pistons alternately by means ot one induction valve, «; and is exhausted through the space between the pistons. The piston and crank connections are such that the steam acts on each piste* ^n"*."*1 , two-thirds of the revolution of the crank, ana hence there are no dead points.

(To be continued.)

THE MANUFACTURE OF SUGAR FROM

BEETS."

II/TTHIN the last fifty years the manufacture

VV of sugar from beet-roots has made rspui

strides, not only in France and Germany, but also

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.... Russia, Belgium, ..,..,*.m, —- European countries. The harvest of l"»-b m France yielded no fewer than 276,000 tons TM TMw sugar, in addition to which there were »*» 10,000,000 gallons of strong spirits, extracted puu from roots and partly from molasses. The valu this sugar and spirit amounted in round nuai to £7,500,000; but besides this *here *«••"?.£ products of 20,000 tons of potash, value U*'' and 1,600,000 tons of pulp, after extraction «" juice, wliich was valued at .t'l ,000.000, and •" eagerlv bonght by fanners for fattening cattle: that the produce of that year's liarvest VTM?K'T" sented in round numbers by ±'9,0< H>,000. **,J~ cess of manufacture usually adopted in Franc* complete to the minutest particular, and so l*jR tageously is each product turned to account B*j there is literally nothing wasted. As the w»ff""' conveying the roots arrive at the manufactory .•*• are carefully weighed, and an account kept of quantity of the raw material received, ft* * waggons the roots pass to the washer. •JjjS sists of a long, cylindrical dram, construct*1', parallel rods of iron, and slightly inclined as revolves in a tank of water. At its lower end is inclined plane, on which the beets fall, •j'jjl passed to the first pulper, where they are cor"" small pieces by revolving knife-blades. *jjj" fragments are then passed into the second P'yPV where, by means of saws, the pulp is nuej comminuted and put into bags made of sui*P, wool, a small quantity only being placed in *8' bag. These sucks are piled one over anotW • separated by trays made of sheet-iron, and so mitted to the action of a press, which extracts great portion of the juice; alter which they arc tat* to the hydraulic press, where the remain"TM squeezed out. The juice is then run through pip into an iron reservoir, connected by means <* valve with the monte-jus, a cylindrical vessel m»

• We are indebted for the tacts of this article to SCrookcj'a recent work "On the Manufacture ol! J» root Sugnr in England and Ireland." Longmans « » •

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of strong boiler plate. By the pressure of Bteom, admitted at the top of this monte-yiu, the juice is forced through a pipe into the defecating pans, where it is rapidly raised to about 180° Fahr., and •' dosed" with milk of lime. It is then brought to the boiling point, when the scum is removed, and submitted to the action of powerful presses, for the purpose of obtaining what juice may be still conI Mined in it. The whole of the juice is then transferred to the carbonatation pan, and carbonic acid gas forced through it. After undergoing this process it is conveyed to the filters, upright cylindrical -vessels, tilled with grauulated bone-black, a section of one of which is seen at Fig. 1. M is a cover, fitting tightly on the top, for the purpose of introducing the bone-black. N is a man-hole for drawiug out the spent bone black, and also for admitting a sieve, covered by a cloth, which is introduced into the bottom of the filter before the bone-black is admitted. S is a pipe for the introduction of steam, pure water, beet-root juice, and syrups into the filter, by means of the pipes F, E, D, C, which are in connection with S, through which the passage of either of these fluids is regulated at will, by means of special taps. The pipe S is also fitted with a small connecting pipe, L, through which the air escapes from the filter, as it gradually fills with liquid. Tho juice, after having traversed the whole Iwdy of bone-black in the filter from top to bottom, is not allowed to run out at the bottom through the pipes W and Y, the cock, V, being kept close, so as to force it to ascend through the upright pipe, U, whence it is allowed to flow out through the open cock, H. The juice is received in a movable funnel, T, which fits on the upright pipes, R and A. If juice is being run through the filter, the funnel is placed on li, and the liquid is thus couveyed either ilirectly to a tank or to the evaporating pans. If syrup is being passed through the filters the funnel is placed on Q, and run to the concentrating pans. V is used for running water into the pipe, Y, which •arrieB it off as waste. After leaving the filters, the clear juice is couveyed to the evaporating pans, where it is reduced to a certain degree of consistency, " syrup," after which it has to be filtered a second time. The old-fashioned evaporating pans have given place to the " triple effect" vacuum pans, a side view of which is given at Fig. 2. The three pans, or bodies, arc marked I., II., III., the three intermediate vapour columns are numbered 1, 2, 8. A is the pipe whieh carries the juice into the first body; B C, is a pipe which carries the juice from the first body to the second, and ti F another which conveys it from tho second to the third body, from whence the pipe F takes it to the montt-jim; K is a pipe and valve for introducing the steam for heating into the first body; E1 is a pipe for running off condensed water; It II is a pipe for conveying spent steam and condensed water to the condenser; Q is the outlet for the hot water of condensation; I' is a glass indicator for the height of the juice in the pan; B is the apparatus for sampling, in

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order to learn the density of the juice; S represents the glass bull's eye for observing tho progress of ebullition ; T is a small funnel for the introduction of melted fat to arrest too violent ebullition; Ti is the small cock for admission of air ; U is a thermometer indicating the temperature of the boiling juice ; V is a special barometer for low pressures for determining the degree of vacuum: X is an indicator of the water accidentally collected in the columns; and Z the pipe for running it out.

Fig. 3 shows a section through the last body of the apparatus represented in Fig. 2, and gives a view of the internal arrangement of a vacuum pan. Tho lower portion of the body, HI., Buowb the disposition of the tubes, around which the stenm for beating the juice circulates. These tubes are insei ted at both extremities into the perforated end-plates. The space above the top plate is the sttnui or vapour chest, where the vacuum is formed, and the steam of the boiling juice collects befor- hein;j carried off. N is the condenser, 0 its injection pipe; M t In- exit pipe for heated condensation water, which is drawn off by an air-pump; A is an upright pipe surrounded by an empty space, B, in which accidental water and liquid collects. The theory of the vacuum pan is very simple, being based on the fact that the juice boils, under the ordinary pressure of the atmosphere, at 212° Fahr., and as this pressure is reduced so the boiling point is proportionately lowered. Now, waste steam, with a teiujieraturo of 212° Fahr. will boil the sugar in the first pan without any vacuum, and passing to the next, in which is a partial vacuum, will boil that at a temperature say, of 19()°; and finally going to the third will cause the BUgar to boil at 150", under the influence of a more perfect vacuum. Thus the concentration of the juice costs nothing for fuel, being all accomplished by the exhaust steam.

The synip, after being boiled and filtered till it reaches the proper consistency, is distributed into a number of crystallizers, and left quiet in a room the temperature of which is kept at 96° Fahr. When crystallization has taken place the contents of the crystallizers are emptied into centrifugal turbines, the outer surface of which is covered with metallic tissue, through the ineshes of which the syrups flow, by tho action of the centrifugal force, while the crystals of sugar arc retained within. In a very short time the sugar may be scooped out of from the inside of the centrifugal, and after being broken up in a " lump-breaking " machine and passed through a screen it is ready for market.

THE MANUFACTURE OF CHLOROFORM.—Accord Ing to the late Jas. Y. Simpson, there is a single manufactory of chloroform, located in Edinburgh, which makes as manv fts eight thousand doses a day, or letwoon two millions and three millions of doses every year—evidence to what an extent tho practice is now carried of wrapping men, women, and children in a painless sleep during some of the most trying moments and hours of human existence.

ON ZYMOTICS.*

ON referring to the Registrar-Generals reports for the last ten years, we find that in England and Wales abont 500,000 peo]ile die every year • of which 600,000, 100,000 die of Uymotic diseases; that is, 20 out of every 100 people who die. die, usually at an early age, of disease which can and ou>;b,t to be prevented. These so-called zymotic diseases have been chosen for the subject of this article, because, they best illustrate what has been said about the prevention and the cure of disease. No approach to any means of curing them has been discovered ■ but of all the complaints known, they are the most easily preventable; in no other group of diseases is there a something which can almost be handled— which is the essence of the complaint, without which the complaint would not exist. It is to the destruction of tliis substance that our efforts in the suppression of these diseases are directed ; for could all the contagious material in the universe be destroyed, these diseases would cease to have a place in the nosology. A knowledge of their natural history is necessary to a comprehension of the means to be employed in preventing their occurrence, and a slight sketch will therefore be given of their course when attacking the individual, and of the circumstances under winch they spread.

The diseases called zymotic—a name which is bad, because bused upon a false theory, but which has become sanctioned from long use—are, in systematic medicine, known as the acute specific diseases; acute, because always of short duration, tending spontaneously to cease at a fixed date from the attack, and never extending over mouths and years like chronic diseases; specific, because they are accompanied by a process peculiar to each one of the group, a process quite mi yentrit, and unknown in the course of other acute complaints. Amongst thorn stand measles, scarlet fever, hooping cough, diphtheria, mumps, typhoid fever, typhus fever, and ftmall pox. Measles may be regarded as a type of this class of complaints. It has a greater tendency to spare the life of the individual than most of the others; it is very widely distributed, and few people reach adult age without having suffered from an attack. The history of the complaint, and of those associated to it, is therefore personally interesting to almost every one.

The acute specific diseases are distinguished by fi ve peculiarities. 1. They occur but once in the life of an individual, who thenceforth is secured from u second attack. 2. They always result from contagion or infection, never arising <lc novo from exposure to cold, or other causes of disease, as bronchitis or rheumatism does. 3. There is always an interval, longer or shorter, between the date when the individual receives the contagion into his system, and the date when he first begins to feel ill. 4. There is an interval between the first feelings of illness and the first appearance of the specific process, the rash on the skin, or the sore throat. 5. The specific disease always runs a sharp well-defined course lasting a certain number of days, and tending to end in the recovery of the patient, at the termination of the specific process. These live characters will now be considered more in detail.

Each disease, as a general rule—and only as a general rule—occurs but once during life. Every mother, for example, knows that when her child has had the measles, or the hooping cough, it will be secure against a second attack. It not unfrequeutly happens, however, that a second attack of measles or smallpox occurs; in these cases, especially the latter, the complaint runs a much less severe course than in the first. In the great majority of individuals, the protection afforded by one of this group of diseases against its recurrence is complete. This immunity from a second attack is one of the most curious problems in medicine. Everyone knows how a part, onee affected with a complaint, is liable to a return on the slightest causes, e. y. a common cold, or a sore throat. With the acute specific, or zymotic diseases, the case is exactly the reverse; and at the present moment there is of this no satisfactory explanation whatever.

• • « « »

Another striking feature in the natural history of these disorders is that they are never known to arise spontaneously, as other complaints do; but their origin is always due to a certain contagious matter. There is no properly authenticated case on record of a person having suffered from an acute spjcific disease without having been in some way infected from another person suffering from the same complaint. Recent discoveries seem to suggest that this contagious matter is a vegetable growth—a fungus. Some observers, especially in Germany, aver that they have been enabled to detect under the microscope the little plant which is the cause of cholera; others assert, that certain fungi found in mouldy straw will produce measles in less than forty-eight hours after inoculation. Sir Henry Holland has thrown out the idea that these diseases are produced by clouds of animalcules passing over a country; and he considers that the way in which an epidemic or contagious fever ad

vanccs. supports this view. The zymotic theory has j ust beeu Btated These opinions are introduced only to show how little is really known about the nature or composition of the contagions material Of its existence, there can be no doubt, but of its form, whether animal or vegetable, whether a ferment, or simply some organic chemical combination, nothing is known. With regard to the mode m which this contagious material is conveyed to individuals, it is a common idea that it is carried through the air, or even that it is produced ik nvro where there are bad suiells, defective drainage, and in low, damp situations. The notion that the air carnes the contagious matter is singularly devoid ot any support from the manner in which these complaints usually spread. When, for example an infectious disease passes from one place to another it moves along the line of traffic, not in the direction nf the wind, but along the course taken by travellers. V* hen a contagious disease leaves a continent for an island, it always makes its first appearance in n seaport. In fact, the contagious material seems capublo of being curried but u very short distance, probably only a few feet, bv the movement of the air; one of the best means of dislnfcctiou is to scud a free current of air through the room or space, fresh air seeming to have the power of destroying or weakening, perhaps by dilution, tho coutagious material. Nor is there any evidence to prove that bad smells, &c, produce these specific diseases anew. There is no doubt that defective drainage, and crowding of people together, predispose to the reception of these specific complaints, and are themselves the direct causes of many and serious illnesses ; but bud sanitary arrangements in a house or a town never generate these epidemic disorders—they must be brought from without, and then, under these bad sanitary conditions, they spread with frightful rupiditv, and cause immense mortality. An instance in proof of this may be found in the hygienic condition of England before the time when the cholera first visited us. Then the sanitary condition wus probahly us bud us could be, yet the cholera did not exist until it was brought over from the continent of Europe, when it spreud rapidly and decimated the country. (To be continued.)

* Written by J. Wickham Legg.M.D., and extracted from The Student.

THE ECONOMICAL PURIFICATION OP
COAL GAS.

MR. F. C. HTLL8, of Deptford, makes the ammoiuacol liquor of the gasworks of sufficient purity to become acheup and effectivepurifyiug agent for depriving gas of its sulphurettedhydrogeu and carbonic acid. The gas liquor, when purified, is run through the common scrubber, and the gas allowed to puss up through the scrubber. It then comes into contact with purified nmmoiiiucul liquor, which deprives it of its impurities, and thus the desired result is obtained and nil the expense of excessive lubour is avoided. The mode of purifying the gas liquor is as follows :—A series of stills or vessels are placed one above another, partly filled with gas liquor to be purified, which runs through these vessels by means of connecting pipes from the top to the bottom, where it is made to boil. By this boiling the carbonic acid and sulphuretted hydrogen mid also a little ammonia are driven off, and pass into the liquor in the next vessel above, by which the ammonia vapour is mostly nbsorbed, but not the curbonic ucid or sulphuretted hydrogen. By pussing these products in like manner through the whole series of vessels, the ammoniacal vnpour driven off from the boiling gas liquor is absorbed by the gas liquor in the higher vessels, and the carbonic acid and sulphuretted hydrogen are left free to pass away whenever desired. If wished, the whole of the gas may be purified entirely by this gus liquor; but us the quantity required would bo considerable! it is perhaps best to purify the gas aliout two-thirds by this process, and then to finish the purification with oxide of iron.

SCIENTIFIC SOCIETIES.

GEOLOGISTS' ASSOCIATION.

AT the meeting of this association, held at University College on Friday the 1st Jnlv, Professor Tennant, F.G.S. (in the absence of the President, Professor Morris), in the chair, the following pnpers were read by Mr. J. Logan Lobley, F.G.S.:—

"Two Days in a .Mining District," " On the Distribution of the British Fossil Brachiopoda."

Adam Murray, Esq., F.G.8., exhibited a eollection'of specimens of ores and other minerals from East Cornwall, us well as :plan and soction of a coppermine.

The first paper contained an account of a brief visit paid to the mining district of east Cornwall, in which both copper und tin miues are very numerous. The author dwelt with evident pleasure on the beautiful scenery of the river Tarnar, which meanders through tho richly wooded valleys on the eastern side of this district, to which the river is of very great service, as it fucibtatos the conveyance of tho ores to the localities where they arc smelted.

From the little town of Calstoek a very large quantity of " dressed " copper and tin ore is annually "shipped.

The first mine visited was a copper-mine at a little distance from the town just mentioned, and here the process of dressing the ore was going on briskly. The dressing is effected by means of washing, era.kink, and "jigging," which operations were fullv described." A largo tin-mine was then visited. The oxide of tin being usually associated with quartz, tnngstate of iron, or wolfram, and other minerals harder and of greater specific gravity than those with which eopperore is generally found, a more elaborate process for dmuicg the ore of tiu is requisite than is necessary for that of copper. It is especially worthy of remark that th<copper lodes are met with in the " kiliag " or Lower Devonian rock, while tiu ore is found only when granite is reached. This is strikingly exampUtted *i Kit's Hill, a bold elevation forming the highest land in east 'Cornwall. The upper part only of this hill U granite, the flanks and base being lower Devonian. Accordingly we find copper-mines around the lower portion of the hill, while the engine-house of a tin-mine crowns the summit.

In this district mines are descended by means of vertical ladders placed in short shafts or " winze* " connecting the "levels "which are worked at regular distances below each other.

One nf these mines, worked to a depth of upwards of 400ft. below the Tamar, wus explored by the author, and the description of the mine uud mode of working out tile lode concluded the paper.

In the second paper Mr. Lobley gave the results of un investigation into the range and distribution of the genera and families of Fossil Brachiopoda in British strata, and exhibited a series of diagrammatic tables embodying the results arrived at, and intended to show by a peculiar orraugeuieut the increment, decrement, and maximum development of each gennu and famih/. The genera and families were arranged in the order of their incoming or earliest appearance in Brit; Ii strata, uud every species occurring in each geological formatiou was separately and distinctly indicated. The number of species indicated in the tables and catalogued in the lists accompanying the paper was upwards of eight hundred. A great number ol these are, however, recurrent species.

On the conclusion of the paper, which was of too detailed and technical a character to he condensed with success, Mr. Henry Woodward, F.Z.S., pointed oat the difficulty that exists in assigning to the genus Calceola its true zoological place. The presence of a so-called uiirrculum seems to be an insuperable objection to this remarkable genus being included in the Cfi-lenterataMr. Woodward expressed his opinion that it was probuhle further research will lead to the condtudon that Calceola is allied to the Hipparitidee.

Professor J. Rupert Jones said the tables would have been more complete had they embraced the results of foreign as well as British research, the area of these islands being too small for satisfactory conclusions respecting the life of any one geological epoch to be drawn from a study of British fossils merely.

Mr. Bath, F.G.S., thought the indication in the tableof the continuance of certain geuera to the present time from evidence obtained from the existence of living species in any of the seas of the globe, while the fossd species indicated were from the British Islands einly. was, unless fully explained ou the tables, calculated to confuse the student. The tables and paper were, however, of such value that he moved that they should be printed by tho association. This w as seconded by III. J. Hopkinson, F.G.S., and carried unanimously.

Mr. Lobley replied to tho objections that had been made, and the chairman, after paying a well merited tribute of praise to the great work ou the Brachiopoda by Mr. Davidson, concluded the proceedings by urging the members of tho association to take advantage of the facilities afforded by the railways for visiting interesting geological localities, and to record their observations iu such papers as the former of the two that had been read that evening. He called for a vote of thanks to the author of the two papers, and toe meeting separated.

Tins was the concluding meeting of the sssaoa 1863—70.

TRACTION.—Mr. A. Thomas savs:—"It Is stated thsl the resistance to draught on a well macadamised road U about 661b. tothe ton, on a good granite pavement 831b. tc. the ton and on a rail abont 81b. to the ton. Now, of course, these figures are calculated for a dead level, a very small gradieut altering the proportion which they bear to each other altogether, and this leads me to aak some of your correspondents to inform me whether where the roads are hilly any advantage results from the use of tramways. Iioes not this want of bite make it harder work for horsesto draw a load up hill on a tramway tlxan on a macadamised road?"

FOWLS v. WORMS.—M. Giot, a French Entomologist, has lately found new employment for fowls. He says that French farmers have, during the past year, complained bitterly of the prevalence of worms, which infest corn and other crops, the highest cultivated fields being the most infested. Fowls are known to be tile most indefatigable worm destroyers, pursuing their prey with extraordinary instinct and tenacity. But fowls cannot conveniently be kept upon every field, xior are tbey_ wanted there at all seasons. Therefore M. Giot has invented a perambulating fowl-house, which is described as follows: "Ho has large omnibuses, fitted up with perches above, the nest beneath. The fowls are shut in at night, and the vehicle is drawn to the required spot, and, the doors being opened every morning, tho fowls are let out to feed during the day in the fields. Knowing their habitation, they enter it at nightfall without hesitation, roost and lay their eggs there.

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