Chapter 4

Another improvement consists in using, when a double line is employed, stretchers or crossheads to keep the flexible girders nearly parallel to each other, so that when necessary the load to be transported may be suspended from or borne by both tram wires jointly or simultaneously, thus permitting a load of greater weight than that for which each single tram wire is intended to be carried over the system. One indisputable claim for confidence in the flexible girder principle is said to be that, although the peculiar combination of parts constitutes a striking and valuable novelty, it contains nothing that has not been proved by the experience of years--nay, generations--to be useful, economic, and reliable. The usual practice followed in erecting suspension bridges is applicable in mounting the line, and the carriers, supports, and carriages may be of any of the usual forms. For the rapid removal of limited loads wire tramways are in universal favor, and are recognized not only as very economic and quickly constructed, but also as being in many cases the only means of transport available except by the adoption of elaborate and costly engineering works.

It has, it seems, been suggested by some who have examined the construction of the flexible girder tramway for mineral and produce traffic that it would be an additional advantage if arrangements were made for the carriage of small loads--half a dozen or so--of passengers, the primary intention being to carry the workpeople backward and forward between comparatively inaccessible mines, works, or plantations and a neighboring village or town. Compared with every other system where the line over which the load travels is elevated, the flexible girder tramway is claimed to possess many advantages--the center of gravity is kept well down, the liability of the wheels leaving the line is reduced to the minimum, the gradients are the easiest that can be obtained, there is an entire absence of jolting and extremely little vibration, and the motion is altogether smooth and regular; yet it is very questionable whether, when human life is at stake, any but an ordinary ground line should be relied upon. A living freight is far more liable than a dead freight to move during the journey; and as the safety of all overhead lines depends upon what is scientifically designated "unstable equilibrium," the flexible girder tramway is not recommendable for passenger lines, although it can, of course, be fitted for passenger traffic, a suitable vehicle and ten or a dozen good stout workmen coming well within a two-ton load, which can be readily carried.

Rope traction or animal traction--practically speaking--is alone available for wire tramways (that is to say, if the trains are each to be propelled by its own locomotive--whether steam, springs, or electricity--the cost of construction and maintenance becomes so serious that overhead lines, however well designed, are no longer economic); and experience gained with rope traction in numerous collieries in the North of England and Lancashire districts--where it is highly appreciated--has shown that, all circumstances considered, the endless rope is preferable. The chief objection urged against wire tramways as hitherto constructed has been that the "sag" of the rope has sometimes caused annoyance to those using the property passed over, and has always added much to the cost of traction, owing to the increased power required for moving the load; this has also resulted in vastly increased wear and tear and the rapid deterioration and destruction of the wire rope. The flexible girder system so reduces the "sag" that the maximum economy and durability are obtained, and the gradients over which the load has to travel can be made as easy and regular as those upon an ordinary railway. This advantage will be the more readily appreciated when it is considered that with a given load on a gradient of 1 in 30 the resistance due to gravity alone is 200 per cent. greater than on a gradient of 1 in 150, and that the retardation and wear and tear due to friction, greater curves, and imperfections increase still more rapidly with increase of gradient, soon rendering the old sagging wire line practically worthless.

To construct an entire line of flexible girders would be not only unnecessary, but so costly as to neutralize any advantage which it may possess, yet for surmounting occasional obstacles the claim made for it--that it will sometimes permit of a line otherwise impracticable being cheaply made--seems justified. One can readily imagine a light narrow gauge line costing £1,000 per mile being laid, for example, between a mine and the shipping place, and that a swamp, river, or valley would cost more to bridge over than the whole line besides. If at this obstacle the trucks or carriages could be lifted bodily, passed along the flexible girder, and again placed on the line the other side of the obstacle, the advantage to be derived is obvious; and as the flexible girder is really little more than a suspension bridge _minus_ the platform, and having but two suspension wires, the cost and the difficulties should both be very small.--_Industrial Review_.

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BOZERIAN'S REFRIGERANT PUNKAS.

Punkas (also called pankasor tankas) are apparatus that serve for fanning rooms throughout the entire extent of English India. These devices consist of a light wooden frame covered with canvas, from the bottom of which depends a fringe. These frames are suspended from the ceiling in such a way as to occupy nearly the entire width and length of the room. To the base of the frame is attached a cord which passes over a wheel, and which is pulled by a Hindoo domestic. After the frame has been lifted, a weight fastened to the lower part causes it to fall back again. The result of the continuous motion of this colossal fan is a coolness that is highly appreciated in a country where the temperature is at times incredibly high, and where, without the factitious breeze created by the punka, living would not be endurable. This breeze prevents perspiration, or evaporates the same as soon as it is formed. Sometimes it sinks to a light zephyr; then, if you are reading or writing, you may continue your work, but in a distracted way, with a moist brow, and with a feeling of annoyance that soon makes you leave book or pen.

Looking around you, you find the punka immovable. The bahi still holds the cord that pulls it, but it is because he has tied it to his hand. He has gently slid to the floor in a squatting posture. He is asleep and you are burning. A vigorous exclamation brings him to his feet all standing, and he begins to pull the punka with all his might, and you have a feeling of ease and coolness. It is like the passage from an attack of fever to a state of comfort in an intermittent disease. So the punka is seen everywhere--in the temple and court room and other public places, as well as in private dwellings. It is one of the first things to astonish the European upon his arrival in India, and it is not long before he has to bless the happy invention.

Although, in a country where the temperature generally reaches, and even often exceeds, 40° C., it is absolutely necessary to obtain by every means possible a factitious coolness without which the Indies would not be habitable for Europeans; and although there is no hesitancy in putting up these punkas everywhere to be maneuvered by bahis, the elevation of the temperature is not such in France that we are obliged to have recourse to such processes. But, without being forced thereto by nature, it is none the less true that we are often the more incommoded by heat in that we are not accustomed to it, and that in southern France, at certain hours of the day, such heat becomes absolutely unbearable. We can, it is true, obtain a little air by moving a fan, but, aside from the fact that this exercise soon becomes tiresome, it prevents the use of the hand that is fanning.

The new apparatus which have just been devised by Mr. G. Bozerian permit of one's fanning himself all day long if he wants to, without any fatigue, and while he is eating, reading, writing, etc.

In one of these apparatus, designed to be used in the open air (Fig. 1), we find a table, a tent, and a fan combined; but as each part is independent, we can have the table and fan without tent, or the fan and pedals alone without table or tent. Under the tent there is arranged a frame which pivots freely in apertures formed in the uprights that support both the tent and table. This frame is connected, through two levers, with the pedals upon which one's feet rest. The motion of the pedals is an alternating one like those of sewing machines; but while in the case of the latter a pressure has to be exerted that soon becomes very tiresome, the motion in Mr. Bozerian's apparatus is so easy that it is only necessary to raise the toes of each foot in succession in order to produce a swing of the fan through the weight alone of the foot that is pressing. The frame, which when at rest hangs perpendicularly, describes about a quarter of a circle when the extremity of the foot is raised about an inch. In consequence of the absence of passive resistances, motion occurs without any stress, and almost mechanically, giving air not only to him who is actuating the fan, but also to his vis-a-vis.

Fig. 2 represents an apartment apparatus designed to be placed in front of a table or desk, in order that one can fan himself while eating or writing. Being mounted upon casters, it can be readily moved about from one place to another. At the extremity of a wooden support, whose height may be varied at will, there is arranged a flexible fan whose handle is fixed near a pulley. A small piece of lead forms the counterpoise of the fan, which is thus completely balanced. Over the pulley runs a cord, each end of which is attached to a pedal. It will be seen that the alternate motion of these pedals must cause a rotation of the pulley in one direction or the other, and that consequently the fan will rise or fall more or less rapidly, and give a quantity of air that varies according to the rapidity with which the toes are moved.--_La Nature_.

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PUNKAS.

[Footnote: Extract from a lecture recently delivered at Bombay.]

By J. WALLACE, C.E.

The function of a punka is to cause a current of air to pass the human body so that the animal heat may escape more rapidly. This has nothing to do with ventilation; for if the punka were used in a closed room, it would still produce a cooling effect on the skin.

Let us for a moment examine into what takes place in this operation, for a clear idea of the cause of our sensations of heat is absolutely necessary to enable us to go directly to the simplest and best form of remedy. The heat we feel, and which sometimes renders us uncomfortable, is produced _within us_ by the slow combustion of the food we eat.

This heat continues to escape from the whole surface of the body during the whole lifetime, and if anything occurs to arrest it to any great extent, the result is fatal.

In cold weather, and especially when there is much wind, the animal heat escapes very rapidly from the body, and extra clothing is used, not for any heat it imparts, but simply because it interrupts the escape of the heat, and thus maintains the temperature of the skin--that part of us which is most sensible of change of temperature. It is a wonderful fact that the heat of the interior of the body varies very little in a healthy man between India and Greenland.

The skin may bear a good many degrees of change of temperature with impunity, but the blood will only suffer a very small variation from the normal temperature of 98-4/10° Fahrenheit without serious consequences.

Well, to keep the skin at an agreeable temperature in India we generally wear a minimum of clothing, and when there is no breeze, we try to produce one with the punka.

The escape of animal heat from the body forms a subject which is much more complicated, and much more important, than the one we have met to consider, but it is impossible within the limits of our time to refer to it, except in the measure that is strictly necessary to elucidate the principles that should control the construction of the punka.

It has often been said that every engineer on his arrival in India sets about improving this useful apparatus; but if we may judge from the endless variety of forms which may be seen in shops and offices, in public and in private buildings, no general principle of construction has been recognized, and the punka, as we see it, seems to depend, for its form, more upon the taste of the workman who makes it than on anything else.

We shall begin by directing our attention to the suspended punka, which is usually hung from the ceiling, and put in movement by a cord. The object of this class of punka is to produce a downward current of air by swinging to and fro, and the best punka is the one which throws downward the greatest quantity of air with the smallest applied force.

The swinging punka is one of the simplest forms of mechanism; it can be fitted up with the most primitive materials, and however badly made, it will always have _some_ effect. This fact has its good and its bad aspects; it brings a certain comfort within the reach of all, but it removes a great part of that _necessity_ which, as we all know, is the mother of invention.

There are some very important natural laws which are illustrated in the punka. The first is that which governs the movement of the pendulum. The number of swings it makes per minute depends on the length of the suspending cords; a pendulum three feet long will swing 62½ times per minute, and a pendulum six feet long will swing 44¼ times per minute. Whether the swings are long ones or short ones, the number per minute is still the same. You cannot, therefore, alter the natural rate of movement of a punka unless you pull it at both sides.

The next law is that which determines that the angles of incidence and of reflection are equal. This in simple language means that it is useless to expect a good downward current of air from a slow moving and heavy punka, with long suspending cords which keep it nearly always in a vertical position to its plane of movement. Striking the air squarely as it does in its forward and backward movement, it throws almost as much air upward as downward, and of course all the air that is propelled in any other than a downward direction represents just so much power wasted.

One more law, and then we may proceed to demonstration.

As the air weighs 0.072 lb. per cubic foot at 82° Fahrenheit, and as a considerable quantity of air is put in motion, the power required to drive a punka depends upon the quantity of air it puts in motion in a given time.

The _useful effect_ is a separate matter; it depends on the amount of air thrown in a downward direction.

To summarize; all punkas of the same size or surface, and going at the same speed, require the same amount of pulling. The best one is that which will throw down more air than any other of the same size.

To obtain the greatest result from the power expended in driving it, the punka should be placed as near as possible to the person to be cooled, as the loss of effect, due to distance, increases not in direct ratio, but in proportion to the square of the distance between punka and person. If at two feet of distance he receives one eighth of the total effect, he will at four feet of distance obtain only one thirty-second part.

In practice, the punka should just clear his head when standing, and the weighting of the curtain should be of some yielding material, so as not to damage any person who might stand in its course.

We shall now proceed to examine several forms of punka, all made to the same size, and, for purposes of comparison, we shall drive them all at the same speed. And in order that their effects may be visible to you, I have prepared an indicator which resembles more than anything else the keyboard of a piano. It consists of a series of balanced levers with blades or keys attached, forming a keyboard four feet long. The levers, each three feet long, are delicately hung on fine brass centers, and each lever is counterbalanced by a weight hung in a vessel of water, which acts as a hydraulic brake, and checks any spasmodic movement in the apparatus.

On the end of each blade is fixed a disk of white Bristol board four inches in diameter, forming a row which faces the audience.

This apparatus is so sensitive that a slight change in the humidity of the atmosphere is sufficient to throw it out of balance.

The power required to drive a punka is nearly all due to the resistance of the air; that part due to the force of gravity, and the friction of the suspending joints, is scarcely worth counting. We may readily observe the effect of the resistance of the air by swinging two pendulums of equal length and having each a large cardboard disk attached. One of the disks shall present its edge to the line of movement, and the other its face.

_Exp. 1._--They are now swinging, and being both of the same gravity length, they should swing together and for an equal length of time. This they would do in a vacuum, but you have already observed that one of them is lagging, and will evidently soon come to a standstill. It is the one _facing_ the air.

If punkas were pulled from both sides, they might be made very much lighter than they are at present, but for the sake of simplicity a single pull is preferred. They must, therefore, be made of such a weight that they will swing nearly as far on the opposite side as they are pulled on the near side; any greater weight is useless and only serves to wear out the suspending cords, which, by the way, are nearly always too numerous and too thick for their purpose.

_Exp. 2._--Here is a panel punka which we shall try to use without the customary swing bar. It is of calico stretched on a light wooden frame, and you will be able to judge if it swings equally on each side of the post which supports it. The irregularity of its movement shows that it is too light, so we shall add, by way of swing bar, a bar of round iron one and a quarter inch thick.

_Exp. 3._--It is now swinging regularly, and experiments have already proved that the swing bar should not be lighter than this one, which weighs four and a sixth lb. per foot of length. Iron is the best material for this purpose, as it offers the smallest surface to the resistance of the air. The length of the suspending cords is usually a matter of accident in the construction of a punka, but a little attention to the subject will soon convince us that it is one of the most important considerations.

The limit of movement of a punka is to be found in the man who pulls it. Twenty-four pulls a minute of a length of 36 inches give in practice a speed of 168 linear feet to the punka curtain. This speed is found to produce a current sufficiently rapid for practical purposes, and twenty-four pulls or beats per minute correspond to a length of suspending cord of fifty inches.

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HOW TO MAKE A KITE WITHOUT A TAIL.

The following is the method of making a kite without a tail: All the calculations necessary in order to obtain the different proportions are based upon the length of the stick, A'A, employed. Such length being found, we divide it by ten, and thus obtain what is called the unit of length. With such unit it is very easy to obtain all the proportions. The bow, K'K, consists of two pieces of osier each 5½ units in length, that form, through their union, a total length of 7 units.

After the bow has been constructed according to these measurements, it only remains to fix it to the stick in such a way that it shall be two units distant from the upper end of the stick. The balance, CC', whose accuracy contributes much to the stability of the whole in the air, consists of a string fixed at one end to the junction, D, of the bow and stick, and at the other to the stick itself at a distance of three units from the lower extremity. Next, a cord, B, is passed around the frame, and the whole is covered with thin paper.

Before raising the kite, the string, which hangs from K', is made fast at K in such a way as to cause the bow to curve backward. This curvature is increased or diminished according to the force of the wind.

Nothing remains to be done but to attach the cord to the balance, and raise the kite.--_La Nature_.

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APPARATUS FOR DRYING FLOUR.

The accompanying drawing represents a simple but effective apparatus for drying flour and ascertaining the quantity of water contained therein. It consists of four pieces, the whole being made of block tin. A is a simple saucepan for containing the water. B is the lid, which only partially covers the top of the pan, to which it is fixed by two slots, a hole being left in the middle for the placing of the vessel which contains the flour to be operated upon, and is dropped in in the same way as the pan containing the glue is let into an ordinary glue pot. C is the spout, which serves as an outlet for the steam arising from the boiling water. D is the vessel in which the flour is placed to be experimented upon; and EE are the funnels of the lid which covers the said vessel, and which serve as escapes for the steam arising from the moisture contained in the flour.

_Directions for use_.--Partially fill the pan with water and allow it to boil. Place a given quantity of flour in the inner vessel, D, taking care first to weigh it. Subject it to the action of the boiling water until it is perfectly dry, which will be indicated by the steam ceasing to issue from the funnels. Then weigh again, and the difference in the weight will represent the quantity of moisture contained in it, dried at a temperature of 212 degrees Fahr., that of boiling water.--_The Miller_.

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APPARATUS FOR MANUFACTURING BOUQUETS.

For some years past, the sale of flowers has been gradually increasing. Into the larger cities, such as Paris for example, they are introduced by the car load, and along about the first of January the consumption of them is extraordinary. All choice flowers are now being cultivated by improved methods that assure of an abundant production of them. What twenty years ago would have appeared to be an antiquated mechanism, viz., an apparatus for making bouquets, has now become a device of prime necessity by reason of the exigencies of an excessive demand.

Mr. Myard, a gardener of Chalon-sur-Saone, and vice-president of the horticultural society of that city, has devised a curious apparatus, which we represent herewith from a photograph.

This bouquet machine, which the inventor styles a _bouquetiere_, consists of a stationary rod (shown to the right of the figure), upon which slides a spool wound with twine, and the lower part of which is provided with three springs for keeping the twine taut. A horizontal arm at the top supports a guide or pattern whose curve is to be followed, on placing the flowers in position. This arm is removed or turned aside after the binding screw has been loosened, in order that the rod to the left that carries the bouquet may be taken out. A guide, formed of a steel ribbon, is fixed to the arm and to its movable rod by means of binding screws, which permit of its being readily elongated. This central rod can be raised or lowered at will, and, owing to these combinations, every desired form of bouquet may be obtained.