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It is cultivated in plantations, and is so much improved by the treatment it receives that a cultivated tree affords three times more of this valuable product than 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 attained 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 knife and a large number of hollow shells, larger than 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 filled 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 MOVEMENTS.
(Continued from page 418.)

239. A method of obtaining a reciprocating

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 again. This has been used as a water meter. 241. 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.

242. 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 continu ously through the spiral passage and discharged at the top.

244. 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 opens 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.

245 and 246. DEctol'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 flow 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 downstroke, lower valve is shut and valve in

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

249. Modern lifting pump. 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 upward. Water can be lifted to any height above this

pump.

250. Ordinary force pump, with two valves. The cylinder is above water, and is fitted with solid piston; one valve closes outlet-pipe, and other closes suction-pipe. When piston is rising suctionvalve is open, and water rushes into cylinder, outletvalve being closed. On descent of piston suctionvalve closes, and water is forced up through outletvalve to any distance or elevation.

251. Force pump, same as above, with addition of air-chamber to the outlet, to produce a constant flow. The outlet from air-chamber is shown at two places, from either of which water may taken. The air is compressed by the water during the downstroke of the piston, and expands and presses out the water from the chamber during the up-stroke.

252. Double-acting pump. Cylinder closed at each end, and piston-rod passes through stuffing-box on one end, and the cylinder has four openings covered by valves, two for admitting water and like number for discharge. A is suction-pipe, and B discharge-pipe. When piston moves on, water rushes in at suction-valve 1 on upper end of cylinder, and that below piston is forced through valve 3 and discharge-pipe B; on the piston ascending again, water is forced through dischargevalve 4, on upper end of cylinder, and water enters lower suction-valve 2.

As one

253. Double lantern-bellows pump. bellows is distended by lever, air is rarefied within it, and water passes up suction-pipe to fill space; at same time other bellows is compressed, and expels its contents through discharge-pipe; valves working the same as in the ordinary force pump. (To be continued.)

THE

WEIGHTS AND MEASURES.

HE following is an abstract from the report of a joint-committee of the International Decimal Association, and one of the Central Chamber of Agriculture has been issued, signed by Lord 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 products and manures, is the cause of considerable inconvenience and loss. The Banbury, Devonshire, Essex, Howdenshire, Kincardineshire, Leicester shire, Malton, Monmouthshire, Norfolk, North of England, North Riding of Yorkshire, Scottish, Warwickshire, and Worcestershire Chambers of

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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 in the United Kingdom, your committee find that a movement has been gaining ground for extending such uniformity among all countries. 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 hundred millions, both 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 as perfect as possible, one not likely to be again altered, and one equally suitable to the general wants of all classes of the community-your 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 and manures, is by adapting our present practice to the metric system.

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be used for blind blocking, gold blocking, or for printing in ink and colours. The method of feed. Tng is a very great advance upon the old system. table A, following the action of a cam, is caused work to and fro, the case to be blocked or printed is placed upon the table to gauges while it is in its

442

ENGLISH MECHANIC AND MIRROR OF SCIENCE.

outward position, the motion of the press then draws | and animal tissues, spiral vessels from dried horse-
the table inwards, which at the end of the stroke, dung, hairs, wings, and legs of insects, detrita of
is caused to stop while the case is blocked; it then
returns the case to the attendant, the table being
ready for successive feeding. This round of me-
chanical movements takes place at the rate of 600
per hour, and in a vast number of
- sides and
instances the entire case-
back-can be worked at once, which, in
the ordinary arming presses, could not
by any possibility be accomplished.
The inking arrangements employed INKINC TABLE
in this press are also exceedingly simple.
Ink used in cloth binding has necessi-
tated 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 fits
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 feed
roller, is caused to pass over the per-
forated bottom of the ink box; it
then becomes speckled with ink, which
it distributes over the circular table D,
and the movement imparted to this
portion by means of the spring catch E
becoming locked in the vertical pins
FF causes it to be most effectually,
distributed, the circular portion moving
the distance of one pin at each stroke.

SPONTANEOUS GENERATION OF LIVING

THINGS.

STEAM ON COMMON ROADS.

the steam used to any great exte WHAT is an engine son that we nowhere practical mechanics, and there is certainly no oth for common road traffic? There is probably problem in steam engineering, which has taxed problem, says the Engineer, in the whole range genuity so long, so much, and yet with such com paratively slight results. Almost inumerable i ventors, dating from Cugnot, have been tryi their hands at it for more than a century. I true that their work has not been without su Steam traction engines now carry the fruition. selves and their ploughing tackle in farm oper tions; they are used for drawing heavy loads i short distances on special bits of road; but the Road engines have never yet fou is nearly all. general application in England; and, after ma different trials at various times, they have almos completely failed in France, in Germany, an America. The multiplicity of the proposals and attempts in this direction is remarkable. We have Savery, and later Dr. Robinson, ten years before Cugnot's trial, proposing the thing. Then Oliver Evans; in 1784 Watt patented the application of his engine to the purpose; William Symington Oliver Evans tried it; and afterwards Murdoch. actually propelled an engine of some size. The most ingenious attempts were made by Trevithick; and, after him, by Gurney, Gordon, Ogle, Dr. Church, and Dietz in France. The curious, and perhaps significant, point about the history of these attempts is that the principal ones were renewel with an interval of a generation between each. Thus, after the first schemes in 1759-69, we find Trevithick working in 1802-4; Gordon, Church, and many more in 1832-6; and, lastly, Boydell, the observation of Tyndall in his recent investiga- Aveling, and others, from 1855-65. We now have tion of dust by a beam of light-viz., that the float- another ingenious plan, but, in spite of all that we nature. This we might have been prepared for, Thompson's road steamers, we are not inclineding particles in the air are chiefly of an organic have lately heard from Edinburgh about Mr. from the specific weight of dried organic material, while we wish him every success-yet to make an relation to the controversy on this interesting enabling such dust to float, when the heavier inor- exception in his favour. In the first place, they I question, Dr. Gull, in his Harveian oration at ganic substances would be deposited. That the in- have for led lay uongh; and, in the second, In fact, isolated cases of the partial the Royal College of Physicians, on June 24 last, fectious diseases spread by emanations from the we do not know the proportion that the excellent said:"The dogma omne vivum ex ovo,' for the sick, must have been long known, and that such roads in and about Edinburgh have contributed to truth of which Harvey so justly contended against emanations are of a solid nature, we may infer from his success. the fanciful notions of his age, cannot perhaps be the fact that they may be dried and conveyed from success of steam power on common roads can now maintained in its integrity. Whether, to use place to place; but in what state, whether as amor- generally be traced to the good state of the roads Trevithick, the greatest genius amongst traction an expression of that day, living things are ever phous material or as germs, we know no more to- in the given locality. produced automatically-that is de novo-through day than was known a thousand years past. No putrefaction or otherwise, is, like the question of new fact bearing upon the propagation of contagi- engine inventors, seems at first to have even bethe limitation or universality of the germ power, os disease has been reached by the recent investi-lieved that railroads are useful for speed and for still a matter upon which opinion is divided; and as gations on dust; nor can we infer the nature of the sake of safety, but not otherwise; every par it is my duty on this occasion to exhort you to in- summer catarrh because the nasal mucus under such pose would be answered by steam on common vestigate nature by way of experiment, I must ask circumstances, and at no other time, was found roads which can be applied to every purpose a you not readily to accept negative conclusions peopled by vibriones, since decomposing mucus is horse can effect." In this there is, of course, an which impose limits where none may really exist. always populous with this common race of infusoria. evident fallacy. The only reason that greater speel The time is passing in which the human The phenomena of fermentation and putrefaction is obtainable on a pair of rails, with a locomotive and the changes observed a on a road without rails, is that the rail offers a hat, mind can remain satisfied to rest under the fetters in dead and decomposing substances afford no its train, than if the locomotive and train were fever process. The the ordin it has imposed upon itself, or to cherish its own explanation of phantasms, as if its very existence depended upon living body in we took an ordinary train of a locomotive and Man knows only what he has observed of matter produced in small-pox is not, as we know, in road offers a soft, rough, and yielding surface. I them. the course of nature' is the notorious dictum of any way comparable to the yeast formed in ferOn the contrary, the microscope riages, turned the flanges off the tyres, and pled science, showing the limit and the mode of the ac- menting fluids. speed on such a roadquirement of our knowledge; the limit as wide as demonstrates that the forms, as for instance in them on an iron road, made with one smooth nature itself; and the mode is but readiness to be various pus, are not different from those con- surface-one long metallic table, in fact-we c taught. Notwithstanding, therefore, the adverse tained in other purulent and innocuous exudations. evidently get the same decision of schools and dogmas, science still occu- Nor have we any reason to conclude that any forms which we may suppose perfectly straight and pies itself with the possibilities of occasional auto- which are observed are germs which convey the ciently wide to get over the difficulty of our And that it should be so, let disease. It is to be regretted that a confusion in of flanges-as on an ordinary line of railway. matic generation. it not raise antagonism in the minds of those terms has been made. Instead of dust and disease soon, therefore, as a locomotive and train were whose pursuits (inquiries) lie in another direc-it ought rather to have been dust and putrefaction, to run on rails, it might have been seen clearly i tion, since the infinity of nature may well include or dust and fermentation, since the relation of dust the locomotive steam-engine did not want imp to disease has not been revealed anywhere in the ing, but that, in order to put steam power a facts which at first seem to be antagonistic. We have lately been rather blamed for not grate inquiry. That the air conveys the material causes roads, it was the roads that wanted improv fully accepting the germ theory of disease; but to of the infectious diseases from the sick to the In fact, only a year or so after his patent for 1 this college the theory is not new, and, I think I healthy, is a notorious fact, which had equal force Trevithick came to the conclusion that steam may add, has not been proved to be true. It will before these enquiries were instituted, though, riages could not be placed on common roads bar impractica be in the remembrance of many present that in the owing to the exigencies of social intercourse, a fact common roads were radically improved and year 1849 a theory was put forth that epidemic more neglected than in times of comparative igno- dered able to bear heavy loads without giving cholera was due to fungi and their germs. Peculiar rance. It is difficult to vindicate exactness in pro- and increasing the draught to an bodies, it was said, had been found in the rice- gress without seeming to be at the same time a amount. Some of the more able later ima

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in

water evacuations, and also in the air and drinking hinderer of it. The onward and the regulating of traction engines saw this, more or less dearly,

This re-railway, though we are not aware that even Boy
forces of a machine, though not incompatible, but and attempted to make the engine carry
necessary, require the nicest balance.
flection suggests itself by the way the spread of dell's traction engine and endless railway are now
infectious diseases has been handled. The theories
it has given rise to have been so easily put forward successful road traction engine of any, we now see
But the spirit of Messrs. Aveling and Porter taking the lead in the

as to thereby create distrust.
science is no favourer of negations. Der Geist
der stets verneint' finds no greater friend in

anywhere in practical use. After making the most

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 ComBriefly, the whole future of the application of mittee of that day for its investigation. The drinkproduction of steam road rollers. ing water of infected places was examined, the air of rooms in which cholera patients were dying was medicine than in theology. Still, it will be admitted steam to common roads clearly lies in the improve approaching it for examination; dust was collected from cob- ance of every proposition, however distinguished same way as rails must be laid down before run admits given them a hard, level surface, one, food, and every imaginable place, to try it for origin and nature of epidemics may be true, but it rendered able to bear heavy weights, and have really germs (for many shapes had been included of proof or disproof, and so has further claim upon as newly as possible that of the rail table. The found the industry of those who have put it forward as a nearer this condition of hardness is approached, this hypothesis demands, we must admit, however, Without going to the length which the more extended will be the use of steam on that we know enough to guide us much further

cholera germs.

The supposed germs, when

in the supposed direful growth), were
to be spores of known harmless fungi and
confervæ, of which, if even the startling num-
ber of thirty-seven and a half millions should
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

has yet to be proved. As an hypothesis,

suggestion.

common roads.

These premisses being granted, the solution of than we have yet gone in the practice of pre- the old problem of applying steam to common

vention."

roads is simply to be found in the general u

the steam road roller.

use of

The steam roller must precede the steam traction engine. Experience Graham ascertained that the rate of diffusion of gases shows that this process of road-making and main

germs of any kind, but broken scraps of vegetable is inversely as the square root of their densities.

tenance gives us a hard level surface, not liable to

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sink and take ruts 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. Much 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.

TH

WINDING WATCHES AND CLOCKS. THE object of the invention of Mr. Christian Lange, of 99, Strand, is to arrange the winding mechanism of watches and clocks in such a manner that it may 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.

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 machines 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 be 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 cautious not to overtask a material that has frequently failed under 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 For the sake of illustration the improvement is inclined. This latter position increases the strain explained as applied to a watch. The wheel, which upon both itself and the jib, but possesses some is geared into and worked by the pinion on which advantages in diminishing the length of the upright the knob at the pendant is fixed, and which is called pillar, and thus requiring less headway. But when the first wheel, is fixed on to one end of an axle cranes are required to lift twenty, and even thirty while the other end of the axle is formed square to tons, it is imperative to employ wrought iron, for take a key. This first wheel gears into a second two principal reasons: In the first place because a wheel, and the two are kept in constant connection more reliable material is necessary to resist strains and gear by means of a piece of steel or other metal of so great a severity, and in the second because fitted over or under them, and on which the centre the peculiar form required cannot be obtained by or stud carrying the second wheel is fixed. This the use of cast iron. In Fig. 1 is represented an piece of steel has its turning centre in common elevation of a wrought-iron bent crane, and an 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 third 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, but 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.

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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 has two arms, one of which carries the stud D, on which works a pinion 2, gearing into a wheel 1 on the spindle B, and the other arm has a pin or projection, against which presses a spring E, with the view 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 out 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

FIG.

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 be 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 load-
ing and unloading the cargoes of ships cannot be
over-estimated. Wrought-iron cranes may be con-
structed 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 plates
being avoided. It is a very simple matter to cut
the end of a small bar to any required angle, com-
pared 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, which
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 numerous, 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 rivetting 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, but 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 which 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 tons, the crane should be 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 mstances the absolute impossibility, of examining the interior after the separate parts have been put together. It may in some 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 even urged with some degree of truth against tubular girders similar to those spanning the Straits of Menai, for although 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 investiga tion 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
T the meeting of this society, held on June 17th,
a paper was read entitled, "On the Reactions
occurring during the Process of Smelting Ores at
Freiburg, Germany," by Persifor Fraser, jun. A paper
was read by E. D. Cope, being "A Partial Synopsis of
the Ichthyology of North Carolina."

Dr. S. A. Genth exhibited photographs of a meteorite from North Carolina. Also a specimen of a meteorite from Rockingham County, 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, &c., which constituted the tailings of the pan of some gold miners in Montana washings were made at 8ft. below the surface of the Territory. It was furnished by some miners, whose

ground.

Prof. Cope exhibited a series of Reptilian remains from the Triassic sandstone of Pennsylvania, from the collection of Chas. M. Wheatley, and re viewed the species described from the American Trias indicating their ordinal relations. He explained that he had discovered the ischium of Clepsysaurus, Lea,

sacrum.

and that indicated that that genus was a Dinosaur, occultation. On the 8th, at 3h. 28m. a.m., the ingress
near Megadactylus. He referred several supposed of the shadow of the third satellite will take place, and
genera to Belodon, including Palæosaurus, of Emmons the shadow of the first will come on at 2h. 52m. a.m.
(not Riley and Stuckbury), Compsosaurus, &c., and in- on the 9th. At half-past three on the next morning
dicated the existence of four well-defined species in the satellite 1 will reappear from occultation.
In the
United States. These were:- B. carolinensis, B. early morning of the 17th the first satellite will dis-
priscus, B. leaii, from North Carolina, and B. lep- appear in an eclipse at 2h. 3m., and the second at 2h.
turus, new species from Pennsylvania. The last was 4m. At 1.29 a.m. on the 18th, the shadow of the first
represented by many parts of the skeleton, including satellite will pass off Jupiter's limb, and will be fol-
limbs, pelvis, ribs, vertebræ, &c. The vertebræ in- lowed by the satellite itself at 2h. 42m. The egress of
dicated that costal articulations were continued to the the second satellite from the planet's face will take
He exhibited three vertebræ of a large cre- place at 1h. 44m. a.m. on the 19th, and the third will
taceous Dinosaurian, which presented immense be occulted at 2h. 19m. The first satellite will be
pneumatic foramina, like those seen in Megadactylus. eclipsed at 3h. 56m. a.m. on the 24th, and during the
He stated that he had already indicated that the early morning of the 25th the shadow of the same
bone regarded by Mantell as the os quadratum of satellite will enter on to Jupiter's disc at 1h. 9m., the
Iguanodon was evidently a vertebra, and that Seeley moon itself following its shadow at 2h. 25m.; while at
had since made it the type of a new genus of 3h. 23m. the shadow will pass off again. After
Dinosauria, under the name of Ornithopsis Hulkei, sup- midnight on the 25th, the third satellite will be
posing it to be Plesiosaurian in affinities, and indicating eclipsed at 1h. 29m. The egress of the shadow of the
the most gigantic member of the class. Prof. Cope second will take place at 1h. 46m., and the ingress of the
showed, however, that the characters were in many satellite three minutes after its shadow has gone off.
important respects similar to those of vertebræ of The first will be occulted at 1h. 53m., and the third re-
Laelaps, and probably Dinosaurian. Megadactylus appear from eclipse at 3h. 37m. Finally, on the 31st, or
and the specimens exhibited confirmed this position. rather during the early morning of September 1st, the
The latter resembled it in the great pneumatic for- ingress of the shadow of the first will take place at
amina, but differed in the much denser structure of the 3h. 3m., and that of the satellite itself at 4h. 22m.
spongy tissue of the cerebra. It was named Pneuma-
tosaurus pelorens; size that of Lælaps aquilunguis.

ASTRONOMICAL NOTES FOR AUGUST.

THE right ascension of the sun at Greenwich, mean noon on the 1st of August, is 8h. 45m. 38-49s., and his declination north, 18° 1m. 31.9s. He is, therefore, situated a little to the east of the star o 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. 4.33s. 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. 26m. 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 portios 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 dise 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 disappear at the moon's dark limb, and reappear at her bright limb 35m. afterwards. On the 17th, the moon's bright limb will occult μ Ceti at 10h. 29m.; the star will emerge from behind the dark limb at 11h. 23m. On the 19th, the moon having passed quite close to 1 Tauri an hour after midnight will at 13h. 14m. occult 2 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 5h. 39m. a.m. on the 7th; with Jupiter 48m. before noon on the 21st; with Mars at 4h. 35m. 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 1h. 15m. 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 1h. 33m. on the 31st. He travels from the confines of Cancer through Leo into Virgo during the month. He is near Regulus at 7.17 in the evening of the 9th, and Virginis at 7h. 56m. in the evening of the 23rd. 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 3 a.m. at the end of it, setting about 6 in the afternoon, or a few minutes afterwards, throughout the whole of August. She souths at 9h. 50m. in the morning on the 1st, and at 10h. 24m. on the 31st. She travels from Gemini right through Cancer. She is in conjunction with Uranus at 24m. past 3 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 31st, 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 6:23 on the afternoon of the 31st, and with the moon, as has been mentioned, on the 23rd. Jupiter, after the first week in August, will rise before midnight, and be an interesting object until sunrise. He souths at 8:32 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. 1m. 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 1h. 31m. a.m. on the 3rd the first and second satellites will, almost simultaneously, reappear from

Saturn, up to the middle of August, is tolerably
favourably situated for observation. During the latter
half of the month, however, he sets 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 south-
Uranus is
east part of Ophiuchus during the entire month.
a 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 6.23 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 μ
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 be-
long 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, 31, Tavistock-
street, Covent Garden, W.C.

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

"I 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 a clutter with this little pittance
of his, will undertake to write the whole body of
physicks: a vice from whence great inconveniences
derive their original."-Montaigne's Essays.

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. 317 et seq.), 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 watercolour drawing with a birch broom, or shaving with a hatchet.

and transmitting the red ones, as evidenced by the
colour of the disc of the setting sun, he will not have
much difficulty in understanding the glowing tint pre-
sented the other night by our satellite during the Innar
eclipse.
After a little puzzling over the expression "vertical
plane," employed by "a Ursa Minoris" in his query
(4351) p. 431, 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 cuts 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 base,
as the circle is only a kind of ellipse with its foci
coincident. Finally, if the cutting plane take such a
direction that, being produced, it would meet the opposite
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 scientific
definitions; but I hope that they will supply your
correspondent with the rudimentary information he
requires.
A FELLOW OF THE ROYAL ASTRONOMICAL SOCIETY.

The best answer I can give to the question of "G. C." (4818, p. 430) is to tell him that on the 31st of this month D'Arrest's comet will be a little to the W.N.W. of e Serpentis, 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 says of the spectrum,

ON MOMENTUM AND ATTRACTION. [119] SIR,-Attraction is universal through all creation, always acting with no intermission, all matter attracting all matter. There is therefore no room for of the heavenly bodies at right angles to the line of atrepulsion; the antagonist is motion. And the motions traction is given and continued by attraction alone. Let the division of forces explain Fig. 1.

1

e

9

2

The moon during the half journey from ƒ through & to a was receiving different degrees of attraction in the direction h c, so it has acquired force enough to go to b; but the attraction a e is now in full force, drav ing it aside, so it arrives at d with the 2nd force, that a e had given it, but in passing through d towards e the new 3rd force de has come into action and is drawing it aside, so it arrives at f, where the 4th force ƒe will draw it aside to go on to h, and again round to a, and so keep on for ever.

When the moon is coming down from apogee the attraction is not quite at right angles, but 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 continually imparting to the moon in perfect equilibrium. So there is no visible cause for alteration.

But the motion of a stone in a sling, Fig. 2, is to he accelerated, so it is forcibly pulled in always in advance or as a tangent to the small circle in which the band moves, and this pulling in increases the urgency toy out till its speed in the large circle fully equals the speed of hand in the smaller circle, then adding his own motion from 2 to 3 he lets go.

CORNELIUS VARLEY.

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