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It is cultivated in plantations, and is so mnch improved by the treatment it receives that a cultivated tree affords three times more of this valuable prodnct thau the wild one. The tree has some resemblance to the ash, with leaves shaped like those of the laurel, of a light green colour, and feels downy to the touch. It is of no great beauty, but is valuable as the source of a very lucrative manufacture.

These trees are capable of supplying the varnish when they have attaiued the age of seven or eight years. The varnish is gathered in the following manner:—About the middle of summer a number of labourers proceed to the plantations of these trees, each furnished with a crooked kuife and a large number of hollow shells, larger thau oyster shells. With their knives they make many incisions in the bark of the trees about two inches in length, and under each incision they force the edge of the shell, which easily penetrates the soft bark and remains in the tree. This operation is performed in the evening, as the varnish flows only in the night. The next morning the workmen proceed again to the plantation; each shell is either wholly or partially tilled with the varnish; this they scrape out carefully with their knives, depositing it in a vessel which they carry with them, and throw the shells into a basket at the foot of the tree. In the evening the shells are replaced, and the varnish again collected in the morning. This process is repeated throughout the summer, or until the varnish ceases to flow. It is computed that the fifty trees, which can be attended by a single workman, will yield a pound of varnish every night. When the gathering is over, the varnish is strained through a thin cloth loosely suspended over an earthen vessel.

MECHANICAL MOVEMBNTS.
(Continued from page 418.)

4JOQ A method of obtaining a reciprocating 40Jt motion from a continuous fall of water, by means of a valve in the bottom of the bucket, which opens by striking the ground and thereby emptying the bucket, which is caused to rise again by the action of a counter-weight on the other side of the pulley over which it is suspended.

240. Represents a trough divided transversely into equal parts and supported on an axis by a frame beneath. The fall of water filling one side of the division, the trough is vibrated on its axis, and at the same time that it delivers the water the opposite side is brought under the stream and filled, which in like manner produces the vibration of the trough back agaiu. This has been used as a water meter.

211. Persian wheel, used in Eastern countries for irrigation. It has a hollow shaft and curved floats, at the extremities of which are suspended buckets or tubs. The wheel is partly immersed in a stream acting on the convex surface of its floats, and as it is thus caused to revolve, a quantity of water will be elevated by each float at each revolu

MECHANICAL MOVEMENTS.

tion, and conducted to the hollow shaft at the same time that one of the buckets carries its fill of water to a higher level, where it is emptied by coming in contact with a stationary pin placed in a convenient position for tilting it.

212. Machine of ancient origin, still employed on the river Eisach, in the Tyrol, for raising water. A current keeping the wheel in motion, the pots on its periphery are successively immersed, filled, and emptied into a trough above the stream.

243. • Application of Archimedes' screw to raising water, the supply stream being the motive power. The oblique shaft of the wheel has extending through it a spiral passage, the lower end of which is immersed in water, and the stream acting upon the wheel at its lower end, produces its revolution, by which the water is conveyed upward continuously through the spiral passage and discharged at the top.

241. Montgolfier's hydraulic ram. Small fall of water made to throw a jet to a great height or furnish a supply at high level. The right-hand .valve being kept open by a weight or spring, the current flowing through the pipe in the direction of the arrow escapes thereby till its pressure, overcoming the resistance of weight or spring, closes it. On the closing of this valve the momentum of the current overcomes the pressure on the other valve, opens it, and throws a quantity of water into the globular air-chamber by the expansive force of the air in which the upward stream from the nozzle is maintained. On equilibrium taking place, the right-hand valve openB and left-hand one shuts. Thus, by the alternate action of the valves, a quantity of water is raised into the air-chamber at every stroke, and the elasticity of the air gives uniformity to the efflux.

215 and 246. D'Ectol's oscillating column, for elevating a portion of a given fall of water above the level of the reservoir or head, by means of a machine all the parts of which are absolutely fixed. It consists of an upper and smaller tube, which is constantly supplied with water, and a lower and larger tube, provided with a circular plate below concentric with the orifice which receives the stream from the tube above. Upon allowing the water to descend as shown in 245, it forms itself gradually into a cone on the circular plate, as shown in 246, which cone protrudes into the smaller tube so as to check the fiow of water downward ; and the regular supply continuing from above, the column in the upper tube rises until the cone on the circular plate gives way. This action is renewed periodically and is regulated by the supply of water.

247. This method of passing a boat from one shore of a river to the other is common on the Rhine and elsewhere, and is effected by the action of the stream on the rudder, which carries the boat across the stream in the arc of a circle, the centre of which is the anchor which holds the boat from floating down the stream.

248. Common lift pump. In the upstroke of piston or bucket the lower valve opens and the valve in piston shuts; air is exhausted out of suction-pipe, and water rushes up to fill the vacuum. In dowustroke, lower valve is shut and valvo iu

piston opens, and the water simply passes through the piston. The water above piston is lifted up. and runs over out of spont at each upstroke. This pump cannot raise water over thirty feet high.

249. Modern lifting pomp. This pump operates in same manner as one in previous figure, except that piston-rod passes through stuffing-box, and outlet is closed by a flap-valve opening up*"4Water can be lifted to any height above this pump. ,

250. Ordinary force pump, with two valves. The cylinder is above water, and is fitted witn solid piston; one valve closes outlet-pip*, andouier closes suction-pipe. When piston is rising suctiouvalve is open, and water rushes into cylinder, onueivalve being closed. On descent of piston sucnonvalve closes, and water is forced up through ouueivalve to any distance or elevation. „

251. Force pump, same a» above, with addition of air-chamber to the outlet, to produce a consum flow. The outlet from air-chamber is shown « two places, from either of which water may * taken. The air is compressed by the water duns, the dowustroke of the piston, and expands m presses out the water from the chamber during tat up-stroke. , (

252. Double-acting pamp. Cylinder closed at each end, and piston-rod passes through stufluig-uo5 on one end, and the cylinder has four openmss covered by valves, two for admitting water and WK number for discharge. A is s»ction-pipe, and c discharge-pipe. When piston moves on, w»teJ rushes in at suction-valve 1 on upper end oi cylinder, and that below piston is forced throng11 valve 3 and discharge-pipe B; on the piston »»• cending again, water is forced through dischargevalve 4, on upper end of cylindor, and water enter* lower suction-valve 2.

253. Double lantern-bellows pump- ^9(e bellows is distended by lever, air is rarefied with111 it, and water passes up suction-pipe to fill space; »| same time other bellows is compressed, and exPe its contents through discharge-pipe; valves working the same as in the ordinary force pump.

[To be continued.)

WEIGHTS AND MEASURES.

THE following is an abstract from the report of a joint-committee of the International Decimal Association, and one of the Central Chamber ol Agriculture has been issued, signed by kord Fortescue, chairman :—" From evidence brought before your committee, it appears that the extreme difference of practice in the weights and measures used in different markets of the United Kingdom, for the sale of grain and other agricultural prodncts and manures, is the cause of considerable inconvenience aud loss. The Banbury, Devonshire. Essex, Howdenslrire, Kincardineshire, Leicestershire, Malton, Monmouthshire, Norfolk, North ot England, North Riding of Yorkshire, Scottish. Warwickshire, and Worcestershire Chambers W

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standard be decided upon* the same should be made compulsory throughout the country.' Besides, however, a general testimony in favour of uniformity of weights and measures iti the United Kingdom, your committee find that a movement has been gaining ground for extending such uniformity among all conntries. And your committee are strongly impressed with the conviction that, dependent as we are upon foreign countries for the supply of grain, other agricultural products, and manures, great advantage would be derived if, in making the necessary change, we could contribute to the realisation of this larger object. It would save time, it would prevent errors, it would greatly facilitate commercial transactions, if grain were quoted in the same manner in every market of the world, and if our merchants and corngrowers could understand the ordinary quotations from Stettin and Odessa as readily as those from their own home markets. Nor is the object far from practical attainment. Your committee have learned that considerable progress has already been made in the great work; that a large number of countries, having an aggregate population of more than two hnndred millions, ¡">th on the Baltic and the Mediterranean seas, and on the Atlantic and Pacific oceans, have agreed in adopting, and are already using, the metric system; that this system has just been established throughout our Indian Empire; and that, in this kingdom, and in the United States of America, the use of the same weights and measures has been made legal and permissive. Under such circumstances—and believing that, if a change is to be made, it is best to endeavour to secure a system ns perfect as possible, one not likely to be again altered, and one equally suitable to the general wants of all classes of the community—yotir committee have come to the conclusion that the best mode of obtaining a real and permanent uniformity in weights and measures applicable to the sale of grain and other agricultural products aud manures, is by adapting our present practice to the metric system.

GOUGHS PRINTING AND ARMING PBESS.

GOUGH'S PRINTING AND ARMING PRESS.

Agriculture are unanimous in their opinion that | voluntary or permissive legislation, and that no steps should be taken for obtaining a uniform ¡ local arrangement or understanding, will enable us »ystem as speedily as possible; and, from louï | to realize the object in view. In the language used experience, your committee are convinced that no by more than one of such Chambers, 'Whatever

THE arming press illustrated in the annexed engraving, and which supersedes band labonr by the use of steam, is the invention of Mr. Gough, of Kirbystreet. Hatten Garden. It is of the rotary class, and as far as we can bear is already working satisfactorily in many places in London and elsewhere.

This press is fitted in such a manner that it can be used for blind blocking, gold blocking, or /0r printing in ink and colours. The method of feed., „g is a very great advance upon the old system. I^e table A, following the action of a cam, is'caused о work to and fro, the case to be blocked or printe'd is placed upon the table to gauges while it is in its outward position, the motion of the press then draws the table inwards, which at the end of the stroke, is caused to stop while the ease is blocked : it then returns the case to the attendant, the table being ready for successive feeding. This round of mechanical movements takes place at the rate of 600 per hour, and in a vast number of instances the entire case — sides and back—can be worked at once, which, in the ordinary arming presses, could not TOP VIEW by any possibility be accomplished.

The inking arrangements employed INKINC TA in this press are also exceedingly simple. Ink used in cloth binding has necessitated somewhat special provisions, owing to its want of ease in working. For its thorough distribution, Mr. Gough places it in a flat metal box B, with a perforated bottom, which tits in an aperture in the inverted ink table C, part of which is circular, and caused to rise and fall with the engraved block. The plane of the block and table being the same, the rollers are free to pass from the table over the block, during its upward and downward movement. There are three rollers: one, the feci! roller, is caused to pass over the perforated bottom of the ink box; it then becomes speckled with ink. which it distributes over the circular table 1). and the movement imparted to this portion by means of the spring catch E becoming locked in the vertical pins F F causes it to be most effectually distributed, the circular portion moving the distance of one pin at inch stroke.

and animal tissues, spiral vessels from dried horsedung, hairs, wings, and legs of insects, detrita of dress, and the like. The results were, in fact, entirely negative of any peculiar bodies to which the epidemic disease could be referred. One general result arrived at at that time, however, agrees with

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SPONTANEOUS GENERATION OF LIVING THINGS.

IN relation to the controversy on this interesting question. Dr. Gull, in his Harveiau oration at the Royal College of Physicians, on June -24 last, said :—" The dogma * omne vivum ex ovo,'for the truth of which Harvey so justly contended against the fanciful notions of his age, cannot perhaps be now maintained in its integrity. Whether, to use an expression of that day, living things are ever produced automatically—that is dr. novo—through putrefaction or otherwise, is, like the question of the limitation or universality of the germ power, still a matter upon which opinion is divided; and as it is my duty on this occasion to exhort you to investigate nature by way of experiment, I must ask you not readily to accept negative conclusions which impose limits where none may really exist. . . . . The time is passing in which the human mind can remain satisfied to rest under the fetters it has imposed upon itself, or to cherish its own phantasms, as if its very existence derwuded upon them. 'Man knows only what he has observed of the course of nature' is the notorious dictum of ■cience, showing the limit and the mode of tho acquirement of our knowledge; the limit as wide as nature itself: and the mode is but readiness to be taught. Notwithstanding, therefore, the adverse decision of schools and dogmas, science still occupies itself with the possibilities of occasional automatic generation. And that it should be so. let it not raise antagonism in the minds of those whose pursuits (inquiries) lie in another direction, since the infinity of nature may well include facts which at first seem to he antagonistic. . . . We have lately been rather blamed for not gratefully accepting the germ theory of disease; but to this college the theory is not new, and, I think I may add, has not been proved to be true. It will be in the remembrance of many present that in the year 1849 a theory was put forth that epidemic cholera wTas due to fungi and their germs. Peculiar bodies, it was said, had been found in the ricewater evacuations, and also in the air and drinking waters of the infected localities. It was confidently asserted that we had substantial facts in support of the theory, and that it fulfilled the conditions required of being both true and sufficient. This college thought the subject of such moment that a sub-committee was formed from the Cholera Committee of that day for its investigation. The drinking water of infected places was examined, the air of rooms in which cholera patients were dying was condensed, that it might afford whatever floated in it for examination; dust was collected from cobwebs, window frames, books, surfaces of exposed food, and every imaginable place, to try it for cholera germs. . . . The supposed germs,'when reallylgerms (for niauy shapes had been included in the supposed direful growth), were found to bo spores of known harndess fungi and conferva?, of whioh, if even the startling number of thirty-seven and a half millions 6houhl be contained in about two drachms of water, as quoted by Tyndall, from Mr. Dancer's examination, it is probable that the whole or repeated units of such millions might be harmlessly swallowed. But for the most part the supposed germs were not germs of any kind, but broken scraps of vegetable

the observation of Tyndall in bis recent investigation of dust by a beam of light—viz., that the Boating particles ill the air are chiefly of an nature. This we might have been prepared lor, from the specific weight of dried organic material, enabling such dust to float, when the heavier inorganic substances would be deposited. That the infectious diseases spread by emanations from the sick, must have been long known, ami tliat such emanations are of a solid nature, we may infer from the fact that they may be dried and convoyed from place to place; but in what state, whether as amor. phous material or as germs, we know no more today than was known a thousand years post. No new fact bearing upon the propagntiou of eontngiOqb disease has been reached by the recent investigations on dust; nor can we infer the nature of summer catarrh because the nasal mucus under such circumstances, and at no other time, was found peopled by vibriones, since decomposing mucus is always populous with this common race of infusoria. The phenomena of fermentation and putrefaction in dead and decomposing substances afford no explanation of the changes observed in a living body in a fever process. The purulent matter produced in small-pox is not, as we know, in any way comparable to the yeast formed in fermenting fluids. Onthe contrary, the microscope demonstrates that tho forms, u for instance ui various pus, are not different from those contained hi other purulent ami innocuous exudations. Nor have we any reason to conclude that any forms which are observed are germs which convey the disease. It is to ho regretted that a confusion in terms has been made. Instead of dust and disease it ought rather to have been dust and putrefaction, or dust and fermentation, since the relation of dust to disease has not been revealed anywhere in the inquiry. That the aii- conveys the material causes of the infectious diseases from the sick to the healthy, is a notorious fact, which had equal force before these enquiries were htsiituted, though, owing to the exigencies of social intercourse, a fact more neglected than in times of comparative ignorance. It is difficult to vindicate exactness in progress without seeming to be at the same time a hindcrer of it. The onward and the regulating forces of a machine, though not incompatible, but necessary, require the nicest balance. Tins reflection suggests itself by the way the spread of infectious diseases has been handled. The theories it has given rise to have been so easily put forward as to thereby create distrust. Rut tho spirit of science is no favourer of negations. 'Der Geist der etets verueint' finds no greater friend in medicine than in theology. Still, it will be admitted that no progress cau be made by the ready acceptance of every proposition, howeTer distinguished the source from which it emauates. The parasitic origin and nature of epidemics may be true, but it has yet to be proved. As an hypothesis, it admits of proof or disproof, and so has further claim upon the industry of those who have put it forward as a suggestion. Without going to the length which this hypothesis demands, we most admit, however, that we know enough to guide us much further than we have yet gone in the practice of prevention."

Graham asi-ertnined that the rate of diffusion of gases is inversely as the square root of thoir densities.

STEAM ON COMMON ROADS. i

WHAT is the true reason that we nowhere aa] the steam engine used to any great extol for common road traffic? There is probably n problem, says the Emjineer, in the whole range i practical mechanics, and theft is'certainly no otbe] problem in steam engineering, which has taxed it genuity so long, so much, and yet v.. -neb coa paratively slight results. I I able .J

ventors, dating from Cnguot, have been trrii) their hands at it for more than a eontury. Itk true that their work has not been without aaaa fruition. Steam traction engines uuw;*aurry theasclves and their ploughing tackle in torn opentions; they are used for drawing heavy load.- f* short distances on special bits of road; but is nearly all. Road engines have never yet fo general application in England; and. after different trials at various times, they have completely failed in France, in Germany, America.' The multiplicity of the proposals Sl! attempts in this direction is remarkaide. We Iuvj Savery, and later Dr. Kohiirs.ui. I D years befor; Cugnot's trial, proposing the thing Then Oui.t Evans; in 17si Watt pateitteu the applicationef his engine to the purpose; William Synungt,,j trii d it; and afterwards Murdoch. Oliver Evans actually propelled an engine of some size. Tbs most ingenious attempts were made by Trevithic.; and, after him, by Gurney, Gordon, Ogle, Dr. Church, anu Dietz in France. The curious, sui4 perhaps siptifieant, point about the history of theattempts is that the principal ones we* rene*-I with an interval of a generation between each. Thus, after the lirst schemes in 175949, Trevithick working in 1802-4; Gordon, Church, and many more in 1893-6; and, la*tly, Boydcll, Aveling, and others, from I8S5-46. We now have another ingenious plan, but. in spit, of all that we. have lately heard from Edinburgh about Mr. Thompson's road steamers, we are not inclined While we wish him every success—vet to make mi exception in his favour. In the lirst place, they have not worked long enough: and, in the second, we do not know the proportion that tho exo&Uezu roads in and about Edinburgh have contributed to his success. In fact, isolated casts of the partial success of steam power ou coinmou roads can generally be traced to the good sUV» o* the roads in the given locality.

TrevTtliick, the greatest genius amongst toacuuu engine inventors, seems at first to have evoi tv lieved that " railroads are useful for speed and lot the sake of safety, but not otherwise; every pur poso would be answered by steam on commeii roads which can he applied to every purpose ■ horse can effect." In this there is, of course, *evident fallacy. The only reason that greater ip is obtainable on a pair of rails, with a locomotive mi its train, than if the locomotive and train wer ou a rood without roils, is that the rail offers i Usmooth, unyielding surface, and that the unli-" road offers a soft, rough, and yielding surface J we took an ordinary train of a locomotive en-i riages, turned the flanges off the tyres, and »them on an iron road, made with one smootl surface—one long metallic table, in fact—we c evidently get the same speed on such a Id which we may suppose perfectly straight cicntly wide to get over the difficulty of ocr ». of flanges—as on im ordinary line of railwm soon, therefore, as a locomotive and train were to run ou rails, it might have been seen clearly ia. the locomotive steam-engine did not want impn ing, but that, in order to put steam pow< r roads, it was the re-ads that wanted inipn..-In fact, only a year or so after his patent for 1== Trevithick came to the conclusion that steam« riages could not be placed on common roods bsfe common roads were radically improved and «dered able to bear heavy loads without giving n\ and increasing the draught to an impractietfe amount. Some of the more able later inFr»nr> of traction engines saw this, more or loss «arfj. and attempted to make the engine carry its own railway, though we are not aware that even Bui dell's traction engine and endless railway »re now anywhere in practical use. After making the most successful road traction engine of any, we now see Messrs. Aveling and Porter taking the lead in tiie production of steam road rollers.

Briefly, the whole futnre of the application o! steam to common roads clearly lies in the improvement, not of the engine, but of the road. Ill thr same way as rails must be laid down before running the locomotive, so must common roads be rendered able to bear heavy weights, and bave given them a hard, level surface, one approaching as ne_'.iy as possible that of the rail table. The nearer this condition of hardness is approached. the more extended will be the use of steam on common roads.

These premisses being granted, the solution of tho old problem of applying steam to common roads is simply to ho found in the general nse of the steam road roller. The steam roller must precede the steam traction engine. Experience shows that this process of road-niakiiig and maintenance gives us a hard level surface, not liable to aink au<l take rnts under the wheels, and affording more than sufficient adhesion for propulsion with smooth wheels. The possibility of applying steam in this way would give us what might be termed a universal tramroad, rendering available for steam power our 200,000 miles of macadamised roads. Mnck in this sense was a passage in a late public speech of such an experienced engineer as Sir Joseph Whitworth, in which he pointed to the improvement of common roads rather than an extension of tramways. The roads are there, and their improvement by the process, instead of involving an outlay of capital, actually greatly reduces the cost of their maintenance. In our especial case the employment of an engine on common roads, able to move about with facility, also means the application of steam to the conveyance of stone from the various deposits along the road; to breaking it up and taking it to the required spots before rolling it down. Of extraordinary value would these applications of steam be in countries with such dear labour as that of America.

WINDING WATCHES AND CLOCKS.

THE object of the invention of Mr. Christian Lange. of i!9. Strand, is to arrange the winding mechanism of watches and clocks in such a manner that it iuay be effected by the knob at the pendant— as applied to a watch—as well as by a key, by which arrangement the advantages are obtained that both the key and the knob may be turned the wrong way without detriment to the watch, while at the same time the hands may be set by means of the knob as well as the common key.

For the sake of illustration the improvement is explained as applied to a watch. The wheel, which is geared into and worked by the pinion on which the knob at the pendant is fixed, and which is called the first wheel, is fixed on to one end of an axle while the other end of the axle is formed square to take a key. This first wheel gears into a second wheel, and the two are kept in constant connection and gear by means of a piece of steel or other metal fitted over or under them, ami on winch the centre or stud carrying the second wheel is fixed. This piece of steel has its turning centre in common with the first wheel, and has an arm to be acted upon for the purpose of setting the hands. On the barrel arbor is fitted a tliird wheel, and the second wheel is kept in gear with it by the pressure of a spring. By turning the knob at the pendant, or a key fitted on the square one way, the watch is wound up, hut by turning it the reverse way, the piece of steel on which the stud of the second wheel is fixed moves concentrically with the first wheel, and the second wheel is lifted out of gear with the third wheel. The setting of the hands is effected by pushing the piece of steel the reverse way to that caused by the above-named spring, by which means the second wheel is thrown out of gear with the third wheel and into gear with a wheel acting into the motion work.

The engraving shows those parts of a watch which form the subject of the invention. The knob

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A at the pendant has on the end of its spindle a pinion which gears into a wheel on the spindle B, which passes through the steel plate C. The latter lias two arms, one of which carries the stud D, on which works a pinion 2, gearing into a wheel 1 on the spindle B, ami the other arm has a pin or projection, against which presses a spring E, with the -new of keeping the wheel 2 in gear with the wheel 3 on the barrel arbor. A small knob F, by being pressed against the arm with the •projection on the plate C, throws the pinion 2 ont of gear with wheel 3 and into gear with the wheel 4 acting into the motion work.

WROUGHT-IRON CRANES.

WHEN it is considered to what very violent jerks and sudden strains a crane is continually subject it is a matter of some surprise that

cast iron should have been so much used in its construction. This can only be accounted for by the fact that a very large margin of superfluous strength is always allowed for in cranes, derricks, and all macliines which have to do with the hoisting and transport of heavy materials. Timber is a good and reliable material for the construction of cranes, but unfortunately its powers of resistance are soon exhausted, and are totally inadequate to perform the onerous duties which are now demanded of it. A cast-iron post and jib, and a wrought-iron tie or arm, constitute the principal features of an ordinary crane. With respect to what has been already stated regarding the employment of cast iron in cranes, it should he borne in mind that the first shock or impetus of a sudden load is borne by the hoisting chain, and transmitted by it to the arm and jib. There is no doubt but that a portion of the wrench or strain affects these parts of the crane, but still the chain manifestly breaks the violence of the jerk. Similarly to its ancient predecessor, timber, the capabilities of cast iron are limited, although they surpass those of the former material. This is not so much owing to the absolute want of strength, as the crushing force of cast iron is very large, as to the somewhat treacherous nature of that substance, which is liable to fracture without evincing the slightest incipient weakness or deflection.' This liability increases with the weight of the load and nature of the strain to which it is subjected, and it is therefore no wonder that engineers are cantious not to overtask a material that has frequently failed imder very disastrous circumstances. The usual form of a crane is well known, and consists of an upright post and sloping jib, and an arm which is sometimes horizontal but more often inclined. This latter position increases the strain upon both itself and the jib, but possesses some advantages in diminishing the length of the upright pillar, ami thus requiring less headway. But wh«n cranes aro required to lift twenty, and even thirty tons, it is imperative to employ wrought iron, for two principal reasons: In the first placo because a more reliable material is necessary to resist strains of so great a severity, and in the second because the peculiar form required cannot be obtained by the use of cast iron. In Fig. 1 is represented an elevation of a wrought-iron bent crane, and an

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inspection of it will at once point out the superior advantages possessed by that particular form. With the straight sloping jib it is impossible to hoist a load, especially if it he of a bulky shape, even nearly up to the top of the crane, but when it is arched, as shown in Fig. 1, it may be raised close up to the under surface of the machine—in fact, as high as the shackle will permit. The utility of this arrangement in loading and unloading the cargoes of ships cannot be over-estimated. Wrought-iron cranes may be constructed either on the solid or open principle. In other words, they may have the sides built up of solid plates, or made similar to those of a warren or lattice girder. The latter are rather the cheaper, as there is a saving effected in the workmanship, a great quantity of cutting and fitting in the phites being avoided. It is a very simple matter to cut the end of a small bar to any required angle, compared with cutting the edge of a large plate to a curved shape. Confining ourselves for the present to the solid-sided or plate crane, the section of one intended for moderate duty is represented in Fig. 2. We shall in another article, refer to the subject of the strains upon these structures, which require very accurate and careful calculation. The section is composed of one or more flange plates, wliich vary in scantling with the strains upon them, and as a rule increase from the summit to the end, where obviously the leverage tending to break the crane across is a maximum. The web or side consists of a series of plates riveted together at the joints by wrappers of T iron, which thus fulfil the double purpose of acting as covering plates for the joints,and as stiffeners for the side or web of the crane. This is one of the disadvantages attending all iron constructions which are based upon the plate or solid-sided system. Whatever may be the

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the weak points. In the plate form the joints in the web are very nnmerous, while in the open or lattice principle there are virtually no joints at all in the web, the bars of which, by virtue of their shape, carry their own stiffening within themselves. A glance at Fig. 2 will at once indicate that a large amount of extra rivettiug is incurred in the solid side. This pinching or drilling, as the case may be, of so many holes in close proximity to one another, must tend to produce a local weakness in the plates, in spite of the best manner in which the riveting may be performed.

The section represented in Fig. 2 would answer only for cranes designed to lift a moderate weight. When the maximum load to be hoisted reaches to twenty tons and upwards, the section alluded to would be too weak for the purpose. It would not fail for want of absolute strength, bnt from want of the requisite rigidity. This is the fault of all single web plate girders, and the same remark applies to lattice girders, in wliich but a single row of diagonal bars is employed, either in the plane of the elevation of the girder or in that of its transverse section. Whenever the load exceeds about twelve tuns, the crane should bo made tubular, with a box-shaped section, represented in Fig. 3. The additional stiffness imparted by thus doubling the sides is at once apparent from a mere inspection of the drawing. There is an objection to this tubular form of crane which applies to all box girders of small dimensions. It is the difficulty, in many instances the absolute impossibility, of examining the interior after the separate parts have been put together. It may in Borne cases be just possible to give the inside a fresh coating of paint, but anything like a proper examination is out of the question. Rust and corrosion have full license to develop themselves unknown and unchecked. This objection is oven urged with some degree of truth against tubular girders similar to those spanning the Straits of Mcnai, for althoagh there is no difficulty in getting at the various interior parts of the bridge, yet the task of examination can never be so thoughly and satisfactorily accomplished as in examples which are open to the light. We must reserve for another article the description and investigation of the manner in which cranes are affected by the strains they undergo, and the method of calculating them.

SCIENTIFIC) SOCIETIES.

AMERICAN PHILOSOPHICAL SOCIETY.

AT the meeting of this society, held on Jane 17th, a paper was read on titled, "On the Reactions occurring during the Process of Smelting Ores at Freiburg, Germany," by Persifor Fraser, jnn. A paper was read by E. D. Cope, being "A Partial Synopsis of the Ichthyology of North Oarolina."

Dr. S. A. Oenth exhibited photographs of a meteorite from North Carolina. Also a specimen of a meteorite from Rockingham Connty, in the same State, which displayed several peculiarities. It appeared to be composed of several kinds of iron. In a portion of it minute crystals of a hard mineral were visible, which he suspected would prove to be iron pyrites. He also exhibited a small quantity of native lead, which he believed to be genuine. It was sent with particles of gold, quartz, Ac, which constituted the tailings of the pan of some gold miners in Montana Territory. It was fnrnished by some miners, whoso washings were made at 8ft. below the surface of the gronnd.

Prof. Cope exhibited a series of Reptilian remains from the Triassic sandstone of Pennsylvania, from the collection of Chas. M. Wheatley, and reviewed the species described from the American Trias indicating their ordinal relations. He explained that he had discovered the ischium of Clepsysaurus, Lea, and that indicated that that genus was the Dinosaur, near Megadactylus. He referred several supposed genera to Belodon, inclnding Palaotaurus, of Emmons (not Riley and Stuckbnry), Comptotaitrue, &c., and indicated the existence of four well-defined species in the United States. These were: — B. carolinenti*, B. priscia, B. leaii, from North Carolina, and B. Upturn*, new species from Pennsylvania. The last was represented by many parts of the skeleton, including limbs, pelvis, ribs, vertebra}, &c. The vertebra) indicated that costal articulations were continued to the Bacrum. He exhibited three vertebras of a large cretaceous Dinosaurian, which presented immense pnonmatic foramina, like those Been in Megadactylu*. He stated that he had already indicated that the bone regarded by Mantell as the os quadratum of Iguanodon was evidently a vertebra, and that Seeley had since made it the type of a new genus of Dinosauria, under the name of Omilhoptit Hulkei, supposing it to be Plesiosaurian in affinities, and indicating the most gigantic member of the class. Prof. Cope showed, however, that the characters were in many important respects similar to those of vertebra) of Laelaps, and probably Dinosaurian. Megadactylus and the specimens exhibited confirmed this position. The latter resembled it in the great pneumatic foramina, but differed in the much denser structure of the spongy tissue of the cerebra. It was named 1'ntumatosauru* peloren*; size that of Lalap* aquilungui*.

ASTRONOMICAL NOTES FOR AUGUST.

The right ascension of the sun at Greenwich, mean noon on the 1st of August, is 8h. 45m. 88-49s., and his declination north, 18° lm. 81-9s. He is, therefore, situated a little to the east of the star i Cancer (vide map, p. 494, vol. x.). The approach of Arcturus and other well-known stars in this part of the sky towards the west in the evening twilight now will indicate to the student the progress of the sun in the ecliptic. The equation of time is additive during the whole of August, becoming subtractive on the 1st of September. On August 1st, 6m. 4-33b. must be added to the time indicated by a sun-dial to obtain mean time; and this quantity diminishes to Om. 12-49s. on the last day, prior (as we have just said) to becoming subtractive on the first day of the succeeding month.

The moon enters her first quarter at 51{m. past 8 a.m. on the 4th, is full at 9h. 18m. a.m. on the 11th, enters her last quarter at 50m. past 7 in the morning of the 19th, and is new at 9h. Mm. on the night of the 26th. She will be four days old at noon on the 1st; five days old at the same time on the 2nd,and so on. Libration will bring some of the south-west portion of her disc into view at 7 a.m. on the 11th, but daylight will of course be too strong to render this of much practical benefit to the ordinary observer. The maximum appearance of the south-east point of her apparent disc will occur at 2 o'clock on the morning of the 24th. There will be three occultations of fixed stars by the moon this month. At 18m. after midnight on the 9th, 4 Capricorni will disapi>ear at the moon's dark limb, and reappear at her bright limb 85m. afterwards. On the 17th, the moon's bright limb will occult M Ceti at lOh. 29m.; the star will emerge from behind the dark limb at llh. 28m. On the 19th, the moon having passed quite close to «l Tauri an hour after midnight will at 13h. 14m. occult 62 Tauri with her bright limb. The reappearance at the dark limb will take place at 18h. 58m. The moon is in conjunction with Saturn at 6h. 89m. a.m. on the 7th; with Jupiter 48m. before noon on the 21st; with Mars at 4h. 86m. on the afternoon of the 23rd; with Uranus at 18m. past 1 a.m. on the 24th; with Venus at 7.10 in the evening of the same day; and finally with Mercury at lh. lorn, on the afternoon of the 28th. Mercury is too close to the sun at the beginning of August to be visible, but owing to his rapid motion to the east he becomes an evening star soon after the middle of the month. He sets, however, at his latest only some three-quarters of an hour after the sun. He is on the meridian at lh. 88m. on the 81st. He travels from the confines of Cancer through Leo into Virgo during the month. He is near Regains at 7.17 in the evening of the 9th, and (J Virginis at 7h. 56m. in the evening of the 28rd. Venus is a morning star throughout the month. She rises a little after 1.80 a.m. at the beginning of the month, and about a quarter to 8 a.m. at the end of it, setting about 6 in the afternoon, or a few minutes afterwards, throughout the whole of August. Shesouths at 9h. 60m. in|the morning on the 1st, and at lOh. Mm. on the 81st. She travels from Gemini right through Cancer. She is in conjunction with Uranus at 24m. past 8 a.m. on the 16th, and, as we have said before, with the moon on the 24th. Mars is a morning star too, southing at 9h. 44m. a.m. on the 1st, and at 9h. 9m. a.m. on the last day of the month. He rises about half-past 1 a.m. on the 1st, and about 1 on the 81st, setting about 6 and 5.15 in the evening of those days respectively. He is in Gemini during the entire month. He is in conjunction with Uranus at 623 on the afternoon of the 81st, and with the moon, as has been mentioned, on the 28rd. Jupiter, after the first week in August, will rise before midnight, and be an interesting object until sunrise. He souths at 8-82 a.m. on the 1st, and at 6.54 a.m. on the 31st. He continues in Gemini during the whole of August.

The phenomena of Jupiter's satellites once more present an agreeable spectacle for the contemplation of the student. At 2h. lm. in the early morning of the 2nd, the first satellite will enter on to Jupiter's disc, and will be followed by its shadow at 8h. 12m. At lb. 81m. a.m. on the 3rd the first and second satellites will, almost simultaneously, reappear from

occultation. On the 8th, at 3h. 28m. a.m., the ingress of the shadow of the third satellite will take place, and the shadow of the first will come on at 2h. 52m. a.m. on the 9th. At half-past three on the next morning satellite 1 will reappear from occultation. In the early morning of the 17th the first satellite will disappear in an eclipse at 2h. 3m., and the second at 2h. 4m. At 1.29 a.m. on the 18th, the shadow of the first satellite will pass off Jupiter's limb, and will be followed by the satellite itself at 2h. 42m. The egress of the second satellite from the planet's face will take place at lh. 44m. Il.iii. on the 19th, and tho third will be occulted at 2h. 19m. The first satellite will he eclipsed at 3h. 56m. a.m. on the 24th, and during the early morning of the 25th the shadow of the same satellite will enter on to Jupiter's disc at lh. 9m., the moon itself following its shadow at _li. Mm. ; while at 8h. 28m. the shadow will pass off again. After midnight on the 25th, the third satellite will be eclipsed at lh. 29m. The egress of the shadow of the second will take place at lh. Mm., and the ingress of the satellite three, minute* after it* *hadow ha* gone off. The first will be occulted at lh. 53m., and the third reappear from eclipse at 8h. 37m. Finally, on the 31st, or rather during the early morning of September 1st, the ingress of the shadow of the first will take place at :ili. gm., and that of the satellite itself at lh. 22m.

Saturn, up to the middle of August, is tolerably favourably situated for observation. During the latter half of the month, however, he gets before midnight, and must be looked for early. He is on the meridian at 8h. 46m. on the 1st, and at 6h. 46m. on the 31st days of the month respectively. He continues in the southeast part of Ophiuchns during the entire month. Uranus is B morning star, but so close to the Sun as to be invisible. He remains in Gemini. Uranus and Mars will be less than half a degree apart at 6.28 on the afternoon of the 31st. Neptune is a morning star, something between 4 and 5 a.m. at the beginning of the month, and between 2 and 3 at the end of it. He is situated a little to the north of ,. Piscium.

From the 10th to the 12th of August, and notably on the former night, watch should be kept for shooting stars, as the earth then at this period encounters that meteoric stream which Schiaparelli has shown to belong to Comet 2 of 1862.

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, 81, Tavistockstreet, Covent Garden, W.C.

All Cheques and Post Office Orders to be made payable to J. Passmore Edwards.

•*! would have every one write what he knows, and as_ much as he knows, but no more; and that not in this only, but in all other subjects: For such a person 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 the clutter with this little pittance of his, will undertake to write the whole body of physicks: a vice from whence great inconveniences derivo their original."—Montaigne'* Kuay*.

CHIEFLY ASTRONOMICAL.

[118] Sir,—I may answer "H. A. C." (4259,p. 406) by saying that it is simply impossible to determine longitude by the aid of an equatorial alone, a sidereal clock or chronometer being absolutely indispensable. Moreover, with these two instruments, in the absence of transit, he can only do his work in an exceedingly imperfect manner. However, assuming him to possess a clock and an equatorial, he must first obtain his local time as accurately as he can, by inserting a transit eyepiece into his telescope, levelling his declination axis with all possible care, and then taking the transit of some star as near as possible to his zenith, inasmuch as (all vertical circles intersecting in the zenith) his central wire will be in the meridian there, however much it may deviate from it in the horizon. If now he can get Greenwich time flashed to the nearest post-office or railway station for him, and compare it with his local time, the difference is his longitude. If not, by observing a sufficient number of occultations of stars by the moon, and reducing his observations in the manner described in "Loomis's Practical Astronomy" (pp. 817 etteq.j, he will get an approximation which may possibly serve his purpose. Using an equatorial to obtain longitude with though, is a little like painting a wateroolour drawing with a birchbroom, or shaving with a hatchet.

The best answer I can give to the question of "G. C." (4318, p. 480) is to tell him that on the Slst of this month D'Arrest's comet will be a little to the W.N.W. of e Scrpentis, where he can fish for it. It will be rather more than a degree from that star. If •' Lunar" (4,334), same page, will consider that a certain small portion of sunlight must be refracted by the earth's atmosphere within the cone of her shadow, and will further call to mind the property possessed by that atmosphere of reflecting the blue >ays of the spectrum,

and transmitting the red ones, as evidenced by t„Kcolour of the disc of the setting son, he will not has, much difficulty in understanding the glowing tint presented the other night by our satellite during the lunar eclipse. . ^——jj ya»

After a little puzzling over the expression "wrt»V«J plane," employed by "a Ursai Minoris" in his query (4351) p. 481, I see that he only uses this form of words to signify what is commonly called the plane of a parabola (or other conic section). I may tell him, then, that in a right cone, the plane that cots it to form a parabola "must be parallel to the slant side of the cone." If the plane cuts both sides of the cone, the section is an ellipse; and this even if it be parallel to the b*LS*. as the circle is only a kind of ellipse with its foci coincident. Finally, if the cutting plane take such a direction that, being prodaced.it would meet the oppo? i i cone (or one with its apex in contact with that of the one cut) the resulting section will be a hyperbola, I am sensible that these are not very rigidly tieientifu definitions; but I hope that they will supply your correspondent with the rudimentary information he requires. A Fellow Of The Royal Astronomical Society.

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The moon during the half journey from/ through i to a was receiving different degrees of attraction in the direction h c, so it has acquired force enough to go & to b ; but tho attraction a c is now in full force, drying it aside, so it arrives at d with the 2ndforce, thi: a e had given it, but in passing through d towards e the new 3rd force d c. has come into action and is drawing it aside, so it arrives at/, where tho 4th force fe will draw it aside to go on to n, and again round to n, and so keep on for ever.

When the moon is coming down from apogee the attraction is not quite at right angles.bat a little in advance, so it accelerates the moon's motion till it passes perigee, and then the attraction slightly retards till it again arrives at apogee. Thus the average of action is quite at right angles to the motion, which it is continnuU/ imparting to the moon in perfect equilibrium. So there is no visible cause for alteration.

But the motion of I stone in a sling, Fig. 2, i* to be accelerated, so it is forcibly pulled in always in a4w»cr or as a tangent to the small circle in which the i»d moves, and this pulling in increases the urgency tn*5 out till its speed in the large circle fully equals we speed of hand in the smaller circle, then adding as own motion from 2 to 8 he lets go.

Cornelius Yarxet.

VARIATIONS IN BAROMETRIC PRESSURE.

[120] Sir,—Will some one kindly inform me as t« where some information can be obtained concerning the influence on the health of animals and plants occasioned by variations in the barometric pressors of the air 1 We are many of us aware by our sensations of the changes in the weight of the atmosphere. Some observations must surely have been made and conclusions arrived at regarding this important subject.

F. B. C.

EMIGRATION. [121] Sir,—I am glad to see the emigration question taken up with so much spirit in your columns, and trust we may glean some good and' usoful know. ledge thereby. Emigration has become one of the leading features of the day, having been forced on all

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