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.
BALL'S FLEXIBLE WIRE TRAMWAY.
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.
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.