Chapter III: Part 3

The New Conveyor Company's conveyor consists of a water-tight trough
through which pass closely-fitting tray plates, attached to a single
chain. These plates are joggled down at one end to receive the flat
front part of the succeeding plate, with the aim of excluding the
breeze from the under part of the carrying plate. The chain is made
entirely of steel with side rollers attached to every third plate, the
plates, 1/4 in. thick, are dished in the shape of a tray, which is less
liable to distortion (from heat) than a flat plate. The speed of
travel is about 45 ft. per minute, while the capacity when handling
coke from 20 ft. retorts is some 30 tons per hour.

A conveyor made by Messrs Graham, Morton & Co., consists of a
travelling tray, the sections of which are joined together by steel
spindles provided with a roller at each end, the latter running on
suitable rails. These sections consist of steel castings with a number
of lateral slots; thus the tray has the appearance of a travelling
grating. To receive the quenching water that escapes through the
grating a trough is placed beneath, and a scraper is used to free the
trough of the dust escaping through the grating.

An interesting conveyor is that of G. A. Bronder, of New York (fig.
11), which has some affinity with the gravity bucket conveyor. It runs
in a water-tight trough which is filled up to a certain height, the
water being slowly circulated by mechanism which resembles a water
wheel. The chain of buckets runs in the trough, the sides forming the
rails for the supporting rollers. The conveyor is covered in along its
whole length, and forms a sort of flue which is connected at each
bench with a number of shoots through which the coke drops into the
conveyor buckets. A pipe of large diameter is connected with an
exhaust fan, which draws away the fumes created by the quenching
process, and sends them into a chimney discharging into the open. The
chain and buckets, being carried on rollers which run on the outer
edge of the trough, cannot come in contact either with the hot coke
or with gritty particles. The chain of buckets is connected by
horseshoe-shaped brackets extending upwards beyond the sides of the
buckets and connected with the links of the driving chains. When the
conveyor is at work the covers of the mouth-pieces are opened and the
coke is fed into the buckets; simultaneously the water valves are
opened and the glowing coke is quenched. Any breeze which may have
fallen between the buckets is collected by a scraper and delivered
into a tank at one end, while the propeller wheel draws the water from
this tank and drives it back to the other end of the trough. The top
strand is the working strand and delivers its load at the terminal.
One important difference between an ordinary gravity bucket conveyor
and this apparatus is that the buckets are here rigidly connected to
the supporting wheels.

The West hot coke conveyor consists of a strongly-built trough in
which a single wide chain partly carries and partly drags the coke. In
the trough is a false bottom, the plates of which are loosely fixed
and kept in position by angle irons on which the chain drags. By two
arm-like extensions the links of the chain are widened right across
the trough. The pitch of the chain is 12 in., so that all the large
pieces of coke are more carried than dragged. The speed of travel is
about 40 ft. per minute.

The Wild conveyor (fig. 12) consists of a cast iron or steel trough 24
to 30 in. wide by 9 in. deep, supported by cast iron brackets to which
the rails that support the strands of the chain are secured. Both
chains run outside the trough, and are secured on either side to the
pushplates, so that only the scraper comes in contact with the hot
coke. Every second link of the 12 in. pitch chain carries a push or
scraper-plate, as shown in illustration.

The De Brouwer hot coke conveyor, which is much used in gas works both
in Great Britain and on the continent of Europe, was invented by a
Belgian engineer. Its construction has undergone many modifications
which experience has shown to be desirable. It consists of a trough of
cast or wrought iron, or mild steel, 20 to 36 in. wide and 3 to 6 in.
deep. Double endless chains run in the corners of the trough, the two
chains being connected together by round cross bars set 30 in. apart,
so as to form a sort of ladder. The hot coke is carried or dragged
along by these bars. One end of the trough is closed and the other is
bent upwards with a view to retaining the quenching water. As the hot
coke is dragged along it is subjected to the action of jets of water.
The conveyor bars, which act as scrapers, sweep the water and the coke
along the trough till the point is reached where the latter curves
upwards. Then the water flows back like a small cascade on the
half-quenched coke, which is thus thoroughly extinguished.
Considerable inclines can be negotiated with this conveyor; in some
installations on the continent of Europe angles of 30 deg. to the
horizontal have been surmounted. In a modification of the De Brouwer
conveyor, installed at the Cassel gas works, the bars which form the
rungs of the conveyor were replaced by cast iron rakes. In another
modified form, the work of F. A. Marshall, to be found in the
Copenhagen gas works, sluices are provided for withdrawing an excess
of water at any point in the trough.

In Great Britain a hot coke conveyor has been designed on similar
lines by Messrs R. Dempster & Sons, Ltd. (fig. 13). The chains are
parallel from end to end, and are composed of identical and
interchangeable malleable cast links. Instead of the chains carrying
the rollers, as is often the case, the chains are themselves carried
and guided by flanged rollers supported from the framework. This
arrangement has the advantage of decreasing the weight of the chain,
as neither the rollers nor the lubricators have to be conveyed, being
stationary. The scrapers are of cast steel and have a rake-like shape
with a view to minimize the breakage of coke.

The essential features in a hot coke conveyor are strength and simplicity, a minimum of wearing parts, interchangeability of wearing surfaces and of worn and broken parts, protection of wearing and working parts from contact with the hot coke, and facilities for keeping the temperature of the conveyor as even as possible, so as to avoid distortion of parts through sudden changes. To attain these latter conditions, it appears essential to construct conveyors of the pushplate type. In these the hot coke is kept continually moving, and thus the good effect is secured of heating the conveyor from end to end uniformly and gradually. This applies particularly to gas works conveyors.

For the service of coke ovens the plate or tray conveyor might be suitable because more gentle. It must be remembered that coke oven conveyors must be of large capacity, and moreover in this case there is more scope for cooling the coke in front of the oven before it is removed to the conveyor, the work being all effected in the open.

_Elevators._--This term is here confined to its proper meaning (in English engineering treatises) of a device for raising material in a vertical or slanting direction by means of buckets attached to endless belts or chains. Lifts for passengers are also sometimes termed elevators (q.v.), and in America the term is also currently applied to the granary or warehouse in which grain is stored (see GRANARIES).

In the bucket elevator, an endless belt or chain runs over terminal pulleys which are fixed at different levels, the distance from centre to centre of these pulleys beings known as the length of the elevator. The design and construction of the elevator will be varied to suit its purpose. Grain elevators are invariably cased in wooden or iron trunks, and the head and foot are also of wood or iron, iron trunks being particularly used in so-called fire-proof buildings. The trunk of the grain elevator (fig. 14) is almost always vertical whilst the band to which the buckets are attached may consist of leather, cotton, hemp, webbing or other suitable substances. When an elevator is intended for lifting heavy materials, such as coal, coke or cement, it is usually set at a slant (figs. 15 and 16), and the endless belt is replaced by one or two strands of endless chain which support the buckets and run over the terminal sprocket wheels. The buckets are attached to the links of the chains, and to prevent these heavy buckets and chains from sagging in their inclined position, rollers or more often short skidder bars are fixed to each bucket, sliding on well-oiled angle bars on each side of the elevator frame.

Both grain and mineral elevators are usually fitted with tightening gears to keep the belt or chain taut; these are generally placed at the lower or well end so as not to interfere with the position of the upper terminal, which is almost invariably the driven one. The tightening of the band at the bottom terminal in the elevator well necessarily alters the space between the terminal pulley and the bottom of the well. This is of little consequence in grain elevators, but for elevators intended to handle coal or any material of varying size the ordinary tightening gear is unsuitable. In such a case the best plan is to attach the elevator-well to the terminal in such a way as to go up or down with the sprocket wheel when the chain is loosened or tightened, while the foot bracket which supports the well and terminal spindle remains a fixture. In order to tighten elevator chains without interfering with either of the terminals, adjustable jockey pulleys at some suitable point may be used, and the desired effect can thus be attained by pressing against the chains and thereby taking up the slack without any interference with either the feed or delivery end.

Elevator buckets must be proportioned to the size and nature of the
material they are intended to carry, and care must be taken to
maintain a uniform feed. This may readily be effected by adjustable
outlets and spouts for grain and the like, and by certain feeding
devices for handling minerals of uneven size. For instance, an
oscillating feed shoot making from 30 to 60 oscillations per minute
can be installed in such a case, and adjusted to deposit at each
backward and forward stroke the exact amount of material adapted to
the capacity of the elevator. The speed of the shoot will naturally
vary with the size of material to be fed. For small coal 60
oscillations would be about the correct speed; for large coal the
speed might be reduced to 30 or less. Speaking generally, care should
always be taken to prevent an undue rush of feed, that is, more than
the elevator can take up, and if tenacious materials are handled,
feeding devices should be employed provided with stirrers or agitators
that will effectually keep the material moving and prevent any larger
lumps from arching over the feed spout, and thus producing chokes.
Elevators should always be fed from that side on which the buckets
ascend, that the stream of material may meet the elevator buckets on
their upward journey. This will prevent the material from filling up
the elevator well and spare the buckets from dredging through an
accumulation of feed. Elevators erected at an incline are best fed at
a point several feet above the well into the chain of ascending
buckets, as under such conditions little will miss the buckets and
drop into the well.

The reason why grain elevators are set vertically, whereas elevators
intended to carry heavy bodies such as coal and ore are generally
inclined at an angle, is that the former can be run at a much greater
velocity than the latter. Grain, for instance, would be uninjured by a
velocity at the delivery end which would fracture coal and seriously
reduce its value, to say nothing of the dust production and the damage
which would be done to the receiving spouts and shoots. Elevators
carrying a light material can be run at a circumferential velocity of
250 to 350 ft. per minute, and if vertically set, will throw the
grain, &c., clear of the elevator into the shoot for its reception. On
the other hand, elevators handling heavy material must be set at an
angle in order to give a clear delivery at a much lower speed of 50 to
60 ft. per minute; in other words, the elevator is so inclined that
the shoot for the reception of the material can be put underneath the
delivering buckets which slowly disgorge their load. To obtain good
results, without taking up too much space, an elevator carrying heavy
material should be set at 40 deg. to 60 deg. to the horizontal. The
same results can be obtained if the main portion of the elevator is
vertical and only the upper portion inclined, or so curved as to bring
the delivery over the shoot. The speed at which vertical elevators
should be run will depend on the diameter of the terminal pulley, that
is, the pulley over which the buckets and bands pass. The centrifugal
force of pulleys revolving at the same speed is in direct proportion
to their diameters, and this is twice as much in a 2 ft. as in a 1 ft.
pulley. It may be taken that the centrifugal force of a pulley will
increase in proportion to the square of its velocity; hence the
centrifugal force of a pulley 2 ft. in diameter running at 50
revolutions per minute will be four times the centrifugal force of a
pulley of the same diameter making only 25 revolutions per minute. It
must not be forgotten that to effect a clean discharge of the buckets
of a vertical elevator, the centrifugal force must be sufficient to
overcome the gravity of the material, because the material thrown off
the delivery pulley in a horizontal direction will be more rapidly
deflected into a parabolic curve the higher its specific gravity. It
follows that for a specifically heavy material a greater centrifugal
force will be required; that is to say, the elevator will have to be
higher speeded than in dealing with a lighter material.

Elevator buckets must be varied according to the nature of the
material; for instance, shallow buckets will be found best for a soft
and clinging material such as flour, moist sugar, sand, small coal,
&c., while for a hard or semi-hard body such as wheat, coal, &c.,
deeper buckets are preferable. On account of their lower speed,
elevators for specifically heavy material require much larger buckets
and chains than grain elevators of the same bulk capacity. The most
economical form of elevator is fitted with a continuous chain of
buckets. Such elevators may be constructed to carry either grain or
minerals. The advantages are greater capacity than an ordinary
elevator of the same dimensions and a more uniform delivery; moreover,
smoother running is secured, since the buckets being close together
need not plunge intermittently through the contents of the
elevator-well.

_Intermittent Conveyors._--The elevators we have been considering, whether used for carrying and distributing coal or grain, have this in common, that they raise material from a lower to a higher level, so to speak, in a continuous stream, the continuity being broken only by the short spaces between the buckets. In the continuous bucket type indeed the stream of material is practically, if not absolutely, continuous. In all these cases the elevator is fed with the material in a continuous stream, and by some mechanical means; whether by band, worm or shoot, is immaterial. Elevators of a somewhat different and more substantial construction may be and are often used for handling filled sacks, barrels, carcases of animals and other bulky objects, which cannot be delivered in a uniform stream, but may have to be conveyed by the elevator intermittently. The ordinary buckets used for grain or coal are replaced by other appliances for gripping and holding the object to be raised from a lower to a higher level, but in principle these appliances are essentially elevators.

Another kind of elevator, known as a _lift_ or _hoist_, is used in mines and quarries and in serving blast furnaces. This is an elevator with one or two buckets. Essentially a heavy load lifter, it is intended for material of too large a bulk to be handled economically by ordinary elevators, and is employed for lifting in either a vertical or, more often, an inclined direction.

For elevating materials, such as large coal, iron ore, limestone, &c., which are too large to be fed into ordinary elevators, and must therefore be handled intermittently, the single bucket elevator or hoist may be used with advantage. But as the essential use of mechanical appliances for handling material is to save human labour as far as possible, that hoist will prove the most economical the operation of which is as automatic as possible. The Americans seem to have been pioneers in the construction of _furnace hoists_, which form the principal elevators of this class, but some excellent examples of the modern furnace hoist are now to be found in Great Britain and elsewhere in Europe. Generally speaking, a furnace hoist consists of an inclined iron bridge girder set at an angle to the upright shaft of the furnace. On this incline are laid rails for the ascent and descent of the bucket, which in this case is known as a skip and is provided with suitable wheels, while the hoisting gear manipulating the skips by a steel rope is erected on or near the ground level. The rails when they approach the upper terminus are usually bent in a more or less horizontal position so as automatically to tilt and thereby unload the skip. To attain the same end, the rails supporting the back wheels of the skips may be bent at the terminus, or the back wheels may have additional wheels of a larger diameter on the other side of their flanges, so that during the ascent and descent the skip runs on its four normal wheels, while at the upper terminus the outer and larger back wheels engage with short lengths of extra rails and thus tilt and effect the automatic clearance of the skip. The dead weight of the skip may be balanced by a counter weight, or double tracks may be laid, so that the empty skip descends on one track whilst the loaded skip is being raised on the other. In this case the distributing hopper at the top of the furnace has an elongated shape so as to take the charges alternately from buckets on either track. Again, the two tracks may be laid one above the other, so that one skip runs on the upper rails and the other on the lower. The two buckets will pass each other at about the centre of the framing, where there will be plenty of room for clearance.

The capacity of the skip will of course depend to some extent on the capacity of the furnace, but an average charge may be put down at 2 tons of ore and lime, or 1 ton of coke. To raise such a charge to a furnace 80 ft. high would require, assuming no counter weight were used, a motor of about 100 h.p. On account of the great speed at which the hoist works, the time taken in raising the charged skip, discharging it, and returning it empty would be only 30 to 40 seconds. The hoist cable runs over guide pulleys placed at the top of the furnace, and the cable is often manipulated by an electrically driven winch in a cabin below. The descent of the empty skip in more modern installations is utilized to effect an even distribution of the feed from the hopper to the furnace by causing the hopper to revolve. To this end the latter is provided with an ingenious mechanism which only comes into operation as the car descends. After every charge shot into the hopper the latter is revolved a few degrees, and this has the effect of giving the delivery of the next load in another direction, so that the charges of the skip are in turn distributed over the whole area of the surface. This is deemed a most essential point in furnace-charging, and it is not one of the least recommendations of this mechanical system of furnace-charging that it can give an even feed without any hand labour whatever. A double hoist has been designed which has the advantage that if one elevator breaks down the work of the furnace is not interrupted. In this system two furnaces are connected at the top by a gantry or bridge, against which, between the furnaces, two inclined elevators are set, so that each can serve either furnace. The skips are on wheels and detachable from the elevator, and are loaded from the ore pockets at the lower terminal and drawn up on a cradle; as this reaches the top where the rails on the gantry correspond with the gauge of the skip or car, the latter is carried by its own weight down a slight incline to either furnace, discharging its contents as it passes over the conical mouth. Another advantage claimed for this system is that the rails of the cradle, when in its lowest position, correspond with the rails which lie parallel to the furnaces and run right under the store bins from which the skip is loaded. The economy to be realized from a furnace hoist will be in direct proportion to the use made of mechanical means of feed conveyance. For instance, the store bins in connexion with such elevators might be economically fed by suitable conveyors, or the material might be brought in self-unloading hoppered trucks into conveniently placed bins, ready to be drawn into the skips.

_Ropeways._--A ropeway has been defined as that method of handling material which consists of drawing buckets on ropes, and by means of ropes, such buckets being filled with the material to be handled and being automatically or otherwise discharged. At what period of history ropeways were first used it is impossible to say, but the fact that pulley blocks, and even wire ropes, were known to the ancients, renders a pedigree of 2000 years at least possible. In more modern days, an old engraving shows a single ropeway in working order in 1644 in the city of Danzig. This, the work of Adam Wybe, a Dutch engineer, was a single ropeway in its simplest form, consisting of an endless rope passing over pulleys suspended on posts; to the rope were attached a number of small buckets, which evidently carried earth from a hill outside the city to the rampart inside the moat. The rope was probably of hemp. Modern ropeways worked with wire ropes date from about 1860, when a ropeway was erected in the Harz Mountains. Since then several systems have been evolved, but in the main ropeways may be divided into the single and double rope class.

The ropeway is essentially an intermittent conveyor, the material being carried in buckets or skips, and practice has proved it an economical means of handling heavy material. The prime cost of a ropeway is usually moderate, though of course it varies with the ground and other local conditions. Working expenses should be low, because under the supervision of one competent engineer unskilled labour is quite sufficient. A ropeway may be carried over ground over which rails could only be laid at enormous cost. To a certain extent ropeways are independent of weather conditions, because their working need not be interrupted even by heavy snowfalls. Their construction is very simple, and there is little gear to get out of order. Sound workmanship and good material will ensure a relatively long life. As an instance, a certain rope in a Spanish ropeway tested new to a breaking strain of 29-1/2 tons was shown after carrying 160,000 tons (in two years' incessant work) still to possess a breaking strain of 27-1/2 tons. The power absorbed by a ropeway is relatively moderate, and under special conditions may be nil. The only demand it makes on the superficial area of the ground traversed is the small emplacements of the standards, which in modern ropeways are few and far between. Wayleaves, or the permission to erect standards and run the line over private land, may of course mean an item in the capital outlay. This circumstance may have checked ropeway construction in Great Britain, but it must also be borne in mind that a large portion of that country is comparatively level and well provided with railways. In building a ropeway it is essential to take as straight a line as possible, because curves generally necessitate angle stations, which mean extra capital and working cost. On the other hand, ground that would be difficult for the railway engineer, such as steep hills, deep valleys and turbulent streams, has no terror for the ropeway erector. There is a case of a ropeway of a total length of 5400 ft. with a total difference in altitude of 2000 ft.; it is claimed this ground could not be covered by a railway with less than 15 m. of line graded at 1 in 40.

Perhaps the simplest type of a single rope system is an endless
running rope from which the carriers are suspended, and with which
they move by frictional contact. Or the carriers may be fixed to this
rope and move with it. The ropeway itself would consist of an endless
rope running between two drums, one, known as the driving drum, being
provided with power receiving and transmitting gear, while the drum at
the opposite terminal would be fitted with tightening gear. The
endless rope is carried on suitable pulleys which themselves are
supported on standards or trestles spaced at intervals varying with
the nature of the ground. The rope runs at an average speed of 4 m.
per hour, a speed at which the bucket or skip can automatically unload
itself. In the double ropeway the carrier runs on a fixed rope, which
takes the place of the rails of a railway. The carrier is fitted with
running heads furnished with grooved steel wheels. The load is borne
by a hanger pivoted from the carrier, and is conveyed along the rail
rope by an endless hauling rope at an average speed of 4 to 6 m. per
hour. The hauling is operated by driving gear at one end, and
controlled by tightening gear at the other end just as in the single
rope system. Double ropeways have been carried in one section over 18
to 20 m., and will transport single loads of 6 cwt. to a ton or more.

Broadly speaking, the single ropeway is not so suitable for heavy
loads and long distances as the double, but in this connexion the work
of Ropeways Limited should be noted, which favours a single rope
system. Their engineer, J. Pearce Roe, introduced multiple sheaves for
supporting the rope at each standard. Thus the rope may pass over one,
two or four sheaves, which are provided with balance beams that have
the advantage of adjusting themselves to the angle caused by the rope
passing over the sheaves, thus equalizing the pressure over a number
of sheaves. A ropeway erected on this system in Japan spans 4000 yds.
of very broken ground; yet only 17 trestles are used, and as each
support is placed as high as possible, no one is of great height. An
altitude of 1130 ft. is reached in a distance of 1200 yds. The ropeway
has a daily carrying capacity of 60 tons in one direction and of 30
tons in the other. Another installation on this system, which serves
an iron mine in Spain, spans 6500 yds. of very rough country, so steep
that in many places the sure-footed mule cannot keep on the track.
This ropeway can deal with 85 tons per hour. The greatest distance
covered by this system, on one section, is 7100 yds., or about 4 m.,
and the carrying capacity is 45 tons per hour.

The motive power required for a ropeway will vary with the conditions.
In cases of descending loads the power generated is sometimes so
considerable as to render it available for driving other machinery, or
it may have to be absorbed by some special brake device. In a ropeway
in Japan of 1800 yds., which runs mostly at an incline of 1 in 1-1/2,
the force generated is absorbed by a hydraulic brake the revolving fan
of which drives the water against fixed vanes which repel and heat it.
In this way, 50 h.p. is absorbed and the speed brought under the
control of a hand brake.

_Aerial Cableways._--The aerial cableway is a development of the ropeway, and is a conveyor capable of hoisting and dumping at any desired point. The load is carried along a trackway consisting of a single span of suspended cable, which covers a comparatively short distance. The trackway may either run in a more or less horizontal direction, i.e. the terminals may be on the same level, or it may be inclined at such an angle that the load will descend by gravity. The trackway or rail rope rests upon saddles of iron or hard wood on the tops of terminal supports, usually known as towers. These towers may be constructed either of wood or iron, and if the exigencies of the work render it desirable, they may be mounted on trolleys and rails, in which case the cableway is rendered portable, and can be moved about, sometimes a great advantage in excavating work. The motive power may be either steam, gas, or electricity. The motor is situated in what is termed the head tower, which is sometimes a little higher than the other or tail tower. Sometimes, but not frequently, the latter is also fitted with a motor. The span between the two towers sometimes extends to 2000 ft., but this is exceptional. Very heavy loads are dealt with, sometimes as much as 8 tons in a single load. The load, which may be carried in a skip or a tray, is borne by an apparatus called the carrier, which is a modification of a running head, consisting of pulleys and blocks and running along the main cable or trackway. The carrier is also fitted with pulleys or guides for the dump line. The carrier is drawn along the main cable by an endless or hauling rope which passes from the carrier over the head tower and is wound several times round the drum of the winding engine to secure frictional hold, then back over the head tower, to the tail tower, returning to the rear end of the carrier. The hoisting rope passes from the engine to the fall block for raising the load. The dump line comes from the other side of the winding engine drum and passes to a smaller block attached to the rear end of the skip or tray. The whole weight of the skip is borne by the hoisting rope, while the dump line comes in slack, but at the same rate of speed. Whenever it is desired to dump the load, the dump line is shifted to a section of the drum having a slightly larger diameter, and being thus drawn in at a higher rate of speed the load is discharged. The engine is then reversed, and the carriage brought back for the next load.

This is in outline the mode of operating all cableways. This appliance has rendered great service as a labour saver in navvying, quarrying and mining work; in placer-mining, for instance, cableways have been found very useful when fitted with a self-filling drag bucket, which will take the place of a great number of hands. Cableways can be worked at a great speed, but a good mean speed would be 500 to 750 ft. for conveying and 200 to 300 ft. for hoisting. A cableway used in excavating work in Chicago was credited with a capacity of 400 to 600 cub. yds. per day at a total cost of 2d. per yard, including labour, coal, oil, waste, &c.

_Coaling Ships at Sea._--In the coaling of ships at sea the cableway has rendered great service. The conditions under which this operation has to be carried out present many difficulties, especially in rough water. One of the chief obstacles is the maintenance of the necessary tension on the cable used in conveying the coal from the collier to the ship. The first test in coaling ships at sea, made by the British admiralty, took place in 1890 in the Atlantic at a point 500 m. south of the Azores in water 2000 fathoms deep. Ten ships of war were coaled, each vessel taking enough coal to enable it to steam back to Torbay, 1800 m. away. In this case the collier was lashed alongside the battleship it was feeding, thick fenders being interposed to prevent damage, but nevertheless as the colliers got light they pitched considerably, and one or two sustained dents in their sides. The ships did not roll, being kept bows-on to the swell, which became heavy before the coaling was completed. The coal was taken in by derricks at the main deck ports. It is clear that had the sea been really rough coaling in this fashion would have been impossible.

The most practicable method of coaling at sea yet devised is the marine cableway of Spencer Miller, which has been tried with some success in the American navy. It is intended for use between vessels 350 to 500 ft. apart. The ship being coaled takes the collier in tow, steaming at the rate of 4 to 8 knots; it has been found that a speed of five knots in moderately rough water will keep the cableway taut and maintain a sufficient distance between the crafts. The collier is fitted with an engine having double cylinders and double friction drums, which is placed just abaft the foremast. A steel rope 3/4 in. in diameter is led from one drum over a pulley at the mast head and thence to a pulley at the head of shear-poles on the vessel being coaled, and brought back to the other drum. The engine moves in the same direction all the time and keeps on winding in both the strands of the conveying rope. Should the two vessels increase the distance between them during the operation of conveying the coal bags, of which two, weighing 420 lb each, may be fastened to the carrier, the extra rope called for is obtained by slipping the upper strand from the drum; this increases the speed of the upper cable. On the other hand should the distance between the vessels be reduced, this operation is reversed, the speed of the upper strand being reduced. To keep the carriage steady on its return empty, a rope, known as the sea-anchor line, is stretched above the two strands of the conveyor line, and under a pulley on the carriage. This cable is attached to the vessel, resting on a saddle on the shear head, whence it leads through the carriage over pulleys at the head of the foremast and mainmast of the collier, running on astern several hundred feet into the sea. A drag or sea-anchor, usually made of canvas and cone-shaped, is attached to the end of this rope. This anchor is used to support the empty carriage on its return to the collier. The diameter of the cone's base is graduated to the speed of the vessels. Thus in a smooth-water test, with a ship steaming at 6 knots, one 7 ft. in diameter was used, while the same anchor answered its purpose very well with a ship doing 5 knots in rough water.

The results given by this system of coaling at sea are relatively satisfactory. Tests made in the United States navy showed that 20 to 25 tons of coal per hour could be delivered by a collier to a war-vessel during a moderate gale. As the ship was under steam all the time and consumed 3 to 4 tons of coal per hour, the balance of the coal bunkered amounted to between 16 and 20 tons per hour, or say 384 tons in 24 hours. It has been suggested that under service conditions the speed of the towing vessel might be increased to 8 or 10 knots an hour; this would of course increase the coal consumption unless the collier proceeded under her own steam. But in such a case the space between the two crafts might be diminished, which would have the effect of causing the cable to sag and of stopping the work, since the conveyor cable to act properly must be kept taut. In Great Britain the Temperley Transporter Company have taken up this method of coaling at sea, working in collaboration with Spencer Miller, and have introduced several improvements in detail. Their system has been tried by the British admiralty.

The coaling of a large vessel by this appliance has the advantage of economizing hand labour. One man is required to work the hoist on the collier, while 20 men will be in the hold filling the bags and delivering them to the deck, where 15 or so will transfer the bags to the lift. One or two men suffice for the overhead work; their station is in the trestle trees. On board the receiving ship a few men will be stationed at the shear head to empty the bags into a canvas shoot, and then return them, while there will be the usual force of bunker trimmers. A ton of coal per minute has been transferred from the collier to the vessel, but for this capacity the ships must not be too far apart, else the rope would not remain taut under such loads. During the Russo-Japanese War, many of the Russian battleships were coaled by means of aerial cableways. The coaling of vessels in this manner seems a success, but it would be desirable to increase the carrying capacity of the cableway or to duplicate the installations.

_Telpherage._--A telpher ropeway or cableway may be defined as a ropeway or cableway worked and controlled electrically, only a rail rope being required besides the live rail or wire from which the electric current is taken. Telpherage was devised by Professor Fleeming Jenkin in 1881, and developed by him in conjunction with Professors W. E. Ayrton and J. Perry. The telpher itself consists of a light two-wheeled truck, carrying the driving motors, which, to avoid gearing or other complicated mechanism, are usually coupled directly to the axles of the telpher. Thus the telpher is a self-propelled electric carrier running on a mono-rail, which, according to the conditions, may be a steel rail or a steel cable. From the telpher are suspended carriers which can be adapted to any kind of material. In many cases the whole load may be suspended from the telpher, or the load, especially if of some length, may be supported at one end by a telpher, and at the other end by what is known as a trailer, or again, two telphers may be installed, one at each end of the load. The telpher carries a small trolley sheave or bow which serves to collect the current from a trolley wire stretched a little above the rail. Frequently the telpher is accompanied by an attendant who manipulates it, but by dividing the trolley wire into sections any system of telpherage may be constructed to work automatically, and by switching off the current from the section in which the telpher is required to stop it can be brought to a standstill at any required point. The speed of the telpher may be readily regulated by the introduction of a resistance between any section of the line and the supply of electricity. The speed may be high, as much as 1500 ft. per minute over the straight portions of the line, but slackened at curves and loading stations, or when approaching a terminus. The required power may be obtained from the mains of an ordinary electric supply with either direct or alternating current, but the former is preferable. The mean expenditure of power in a working day is said to average (including electrical hoisting) 1 H.P. per ton of average load.

The uses of telpherage are many and various. In factories and warehouses, where the buildings are scattered, it has been installed with excellent results. Being essentially an overhead system, there is a saving of floor space, the ground not being obstructed by trucks or trolleys. The same reasons which render ropeways an economical means of handling such material as coal, ore, stone, slate, &c., between the mine or quarry and the rail or barge, may be adduced in favour of telpherage. For the unloading of railway trucks in a crowded goods-yard it is undoubtedly applicable. Any kind of tipping or hoisting operations can be automatically effected by its aid, and any sort of grab may be used in dealing with such materials as sand, clay or gravel. Telpherage is clearly a labour-saving method of handling materials, but of course the exact conditions under which any system is to be used need careful study, while the economy to be effected by the installation of a telpher line must to a great extent depend upon the available supply of electrical energy. (G. F. Z.)

FOOTNOTE:

[1] The illustrations in this article are taken, by kind permission,
from the _Proceedings of the Institution of Civil Engineers_.

CONVOCATION (Lat. _convocatio_, a calling together), an assembly of persons met together in answer to a summons. The term is more usually applied in a restricted sense to assemblies of the clergy or of the graduates of certain universities.

In the American Protestant Episcopal Church a convocation is a voluntary deliberative conference of the clergy; it has no legislative function, and like the convocation of a university, assembles primarily to discuss matters of common interest.

In England the name "convocation" is specifically given to an assembly of the spirituality of the realm of England, which is summoned by the metropolitan archbishops of Canterbury and of York respectively, within their ecclesiastical provinces, pursuant to a royal writ, whenever the parliament of the realm is summoned, and which is also continued or discharged, as the case may be, whenever the parliament is prorogued or dissolved. These assemblies consist of two Houses, an upper and lower. In the upper house sit the archbishops and bishops, and in the lower the deans and archdeacons of every cathedral, the provost of Eton College, with one proctor elected by each cathedral chapter and two by the beneficed clergy in each diocese in the province of Canterbury (in the province of York two proctors are elected by each archdeacon), with a prolocutor at their head. When and how this convocation originated is not historically clear. This much is known from authentic records, that the present constitution of the convocation of the prelates and clergy of the province of Canterbury was recognized as early as in the eleventh year of the reign of Edward I. (1283) as its normal constitution; and that in extorting that recognition from the crown, which the clergy accomplished by refusing to attend unless summoned in lawful manner (_debito modo_) through their metropolitan, the clergy of the province of Canterbury taught the laity the possibility of maintaining the freedom of the nation against the encroachments of the royal power. It had been a provision of the Anglo-Saxon period, the origin of which is generally referred to the council of Clovesho (747), that the possessions of the church should be exempt from taxation by the secular power, and that it should be left to the benevolence of the clergy to grant such subsidies to the crown from the endowments of their churches as they should agree to in their own assemblies. It may be inferred, however, from the language of the various writs issued by the crown for the collection of the "aids" voted by the _Commune Concilium_ of the realm in the reign of Henry III., that the clergy were unable to maintain the exemption of church property from being taxed to those "aids" during that king's reign; and it was not until some years had elapsed of the reign of Edward I. that the spirituality succeeded in vindicating their constitutional privilege of voting in their own assemblies their free gifts or "benevolences," and in insisting on the crown observing the lawful form of convoking those assemblies through the metropolitan of each province.

The form of the royal writ, which it is customary to issue in the present day to the metropolitan of each province, is identical in its purport with the writ issued by the crown in 1283 to the metropolitan of the province of Canterbury, after the clergy of that province had refused to meet at Northampton in the previous year, because they had not been summoned in lawful manner; whilst the mandates issued by the metropolitans in pursuance of the royal writs, and the citations issued by the bishops in pursuance of the mandates of their respective metropolitans, are identical in their purport and form with those used in summoning the convocation of 1283, which met at the New Temple in the city of London, and voted a "benevolence" to the crown, as having been convoked in lawful manner. The existing constitution of the convocation of the province of Canterbury--and the same observation will apply to that of the province of York--in respect of its comprising representatives of the chapters and of the beneficed clergy, in addition to the bishops and other dignitaries of the church, would thus appear to be of even more ancient date than the existing constitution of the parliament of the realm.

Contest between spirituality and crown.

From this period down to the eleventh year of the reign of Edward III. there were continual contests between the spirituality of the realm and the crown,--the spirituality contending for their constitutional right to vote their subsidies in their provincial convocations; the crown, on the other hand, insisting on the immediate attendance of the clergy in parliament. The resistance of the clergy to the innovation of the "praemunientes" clause had so far prevailed in the reign of Edward II. that the crown consented to summon the clergy to parliament through their metropolitans, and a special form of provincial writ was for that purpose framed; but the clergy protested against this writ, and the struggle was maintained between the spirituality and the crown until 1337 (11 Edward III.), when the crown reverted to the ancient practice of commanding the metropolitans to call together their clergy in their provincial assemblies, where their subsidies were voted in the manner as accustomed before the "praemunientes" clause was introduced. The "praemunientes" clause, however, was continued in the parliamentary writs issued to the several bishops of both provinces, whilst the bishops were permitted to neglect at their pleasure the execution of the writs.

Five characteristic periods.

The history of the convocation of the province of Canterbury, as at present constituted, is full of stirring incidents, and it resolves itself readily into five periods. The first period, by which is meant the first period which dates from an epoch of authentic history, is the period of its greatest freedom, but not of its greatest activity. It extends from the reign of Edward I. (1283) to that of Henry VIII. The second period is the period of its greatest activity and of its greatest usefulness, and it extends from the twenty-fifth year of the reign of Henry VIII. to the reign of Charles II. The third period extends from the fifteenth year of the reign of Charles II. (1664) to the reign of George I. This was a period of turbulent activity and little usefulness, and the anarchy of the lower house of convocation during this period created a strong prejudice against the revival of convocation in the mind of the laity. The fourth period extends from the third year of the reign of George I. (1716) to the fifteenth year of the reign of Queen Victoria. This was a period of torpid inactivity, during which it was customary for convocation to be summoned and to meet _pro forma_, and to be continued and prorogued indefinitely. The fifth period may be considered to have commenced in the fifteenth year of the reign of Queen Victoria (1852).

First period.

During the first of the five periods above mentioned, it would appear from the records preserved at Lambeth and at York that the metropolitans frequently convened congregations (so called) of their clergy without the authority of a royal writ, which were constituted precisely as the convocations were constituted, when the metropolitans were commanded to call their clergy together pursuant to a writ from the crown. As soon, however, as King Henry VIII. had obtained from the clergy their acknowledgment of the supremacy of the crown in all ecclesiastical causes, he constrained the spirituality to declare, by what has been termed the Act of Submission on behalf of the clergy, that the convocation "is, always has been, and ought to be summoned by authority of a royal writ"; and this declaration was embodied in a statute of the realm (25 Henry VIII. c. 19), which further enacted that the convocation "should thenceforth make no provincial canons, constitutions or ordinances without the royal assent and licence." The spirituality was thus more closely incorporated than heretofore in the body politic of the realm, seeing that no deliberations on its part can take place unless the crown has previously granted its licence for such deliberations. It had been already provided during this period by 8 Henry VI. c. 1, that the prelates and other clergy, with their servants and attendants, when called to the convocation pursuant to the king's writ, should enjoy the same liberty and defence in coming, tarrying and returning as the magnates and the commons of the realm enjoy when summoned to the king's parliament.

Second period.

Sheldonian compact.