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ROF. ALEXANDER GRAHAM BELL, the inventor of the telephone, has for several years past been deeply absorbed in an effort to solve the problem of aërial navigation; and, as a means to this end, he has invented a new type of kite which is in itself decidedly interesting, and which, all other considerations aside, is bound to prove highly useful in this age of scientific kite-flying for weather forecasting and other purposes. Incidentally he has brought forward an idea which is not only a distinct advance in aërostatics, but is in many respects an application of principle new to science.

The inventor feels confident, moreover, that he is on the direct road to a solution of the problem of navigating the air, and hopes to bring about this consummation before very long. He has made arrangements for a test in the near future of a motor that he has invented for use in connection with his style of kites, in order to evolve a flying machine which will be completely under the control of the operator at all times. The dirigible. balloon, which has served as the foundation for the experiments of Santos-Dumont and many another inventor, has no place in Professor Bell's calculations. All his work has been along the line of finding a solution by means of kite structure.

When Professor Bell entered upon his investigation he found that all existing box kites and flying machines of this order were defective in two ways. For one thing, the box kite is braced in a horizontal and vertical direction, but not otherwise, so that cross supports have to be introduced in the frame, which increase the weight without adding to the flying power, and at the same time operate as an obstacle to the wind. Secondly, the box-kite type of airship increases in

PROFESSOR BELL DEMONSTRATING THE TETRAHEDRAL PRINCIPLE.

explanation of the recent failure of the aeroplane invented by Professor Langley of the Smithsonian Institution, small models of which were operated with a degree of success that did not attend the experiments with the full-sized machine.

The obvious objections to the box-kite form of construction led Professor Bell to construct a kite the frame of which presents the form of a triangle no matter from what side it is viewed. In other words, the frame is a perfect tetrahedron, which is defined by the dictionary as "a solid bounded by four plane triangular surfaces, and having therefore six edges

and four verticals." The best idea of the characteristics of such a unit of construction may be gained by constructing an experimental tetrahedron from toothpicks or small pieces of wood all of equal size and length. Three of these pieces of wood are bound together in the form of a triangle; and then, in each of the three. corners of this foundation triangle, is fastened one end of another of the uniform-sized pieces. The tops of the three

BELL TETRAHEDRAL KITE IN AIR.

uprights are then drawn together and fastened much after the fashion of the poles of an Indian tepee.

Simple tests will demonstrate that such a structure possesses surprising strength in proportion to the size and stability of the individual pieces of which it is composed. Indeed, a kite frame made up of several of these tetrahedrons, which was recently fashioned by Professor Bell, and which, being constructed of aluminum, weighed little more than three pounds, yet supported, without any evidence of strain, the weight of a man weighing 160 pounds. The main advantage, however, which Professor Bell has gained in

his new kite structure, is found in the fact that it is self-braced in every direction, and that the lifting power increases proportionately with the increase of weight.

A kite of the type devised by Professor Bell, it should be explained, is composed of a number of these tetrahedral units. One of the advantages claimed for this class of construction is that the units may be grouped in any form desired, just as a person can build a house of any design. The kites will ascend when apparently there is scarcely a breath of air stirring, and they are very easily managed when in the air. The kite frames are covered with silk or other material of light weight but strong texture. Only the smallest-sized kites are handled by means of cord. Steel wire managed from a windlass is utilized in the case of the larger kites. At his great laboratory at Burdetts, Nova Scotia, where he spends his summers, Professor Bell has kites constructed in accordance with his new principle, which have readily lifted to a considerable height a man weighing 200 pounds.

Professor Bell does not wish the public to gain the impression that he has constructed a full-fledged flying machine. He says modestly that his experiments have not yet passed the kite stage; but he is confident that when the problem of overcoming gravity is solved, the tetrahedral principle of construction will be found to have advantages over the ordinary flat-surface aëroplanes in the matter of cost and weight. Certainly there is much to be expected from his discoveries, since the tetrahedron is the only known unit of construction which offers corresponding increase of lifting power with increase of weight.

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INCE THE ADVENT of individual motor-driven machine tools, the successful application of magnetic clutches has made possible the operation of an entire machine shop concerning which it may be said "There is neither line shaft, counter-shaft, nor belt therein."

The utilization of magnetic clutches in driving planers has made a decided difference in the economical operation of these machines, as it has increased the output by making possible a variety of speeds, the operator being enabled to

or offset. A test was made on a 96-inch planer by setting it so that it would run the tool within 1-32 inch of a shoulder; one hundred strokes were made, and the reverse did not vary enough to allow the tool to touch.

In using these clutches, a machine can be thrown out of action from any number of points at any distance, depending on the number of switches placed in the clutch circuit.

The current required by the clutches is surprisingly small considering the amount of power transmitted; on a cer

change the speed to suit the work. The planers can be run at a much higher speed than formerly, as there are no belts to slip or burn, and, in securing high speeds on belt-driven planers, the belts would have to be made so heavy that considerable difficulty would be experienced in shifting them.

Magnetic clutches, moreover, are very positive in their operation, so that it is possible to work very close to a shoulder

tain planer it required only 75 ampere to pull two cuts through cast iron, each being 3-32 inch x 22 inch, at the speed of 14 feet 3 inches per minute.

This cut does not really indicate how much the clutches will pull as it is just the ordinary work accomplished by the machine mentioned. One of the clutches in use on this planer was tested by putting a strain of 60,000 pounds on it in an attempt to separate the armature from

the magnet. How much more than this it would have successfully withstood, cannot be stated, as the parties making the test would not put any greater strain on their apparatus. This test was made on a 33-inch clutch.

In the accompanying illustration of a 36-in. x 36-in. planer, it will be noticed that there are three gears of different diameters on the left-hand clutch, and there is a field rheostat on the side of the housing of the planer; this will give three different speeds by changing the gearing, and a variety of intermediate speeds from field regulation on the driving motor.

The driving member, in this case, is an ordinary shunt-wound motor driving a pair of clutches through what is known as a "five-gear reverse.' The right-hand clutch controls the return of the platen; and, as the driving and driven gears are of about the same size, a very high speed is obtained.

A magnetic brake is shown at the right of the clutches, and is a very important adjunct to this equipment; should the planer be working very close to the limits of its stroke and the power fail, the platen cannot drift beyond safe limits, as the brake will set and stop the machine instantly. The brake also comes in very handy in setting up work, as the operator can depend upon it to stop the machine. the instant he opens the switch.

Magnetic clutches have been very successfully applied to machines for tapping out pipe fittings; in these machines the

taps are run in a certain distance, and then reversed to run them out. The tapping machines run at such high speeds that ordinary mechanical or friction clutches will not stand up to the work, or, if the clutch is made heavy and positive enough to do the work, it soon tears the machine to pieces; every time the mechanical clutches would reverse, the jar would affect the entire shop. Since magnetic clutches have been applied, however, the machines reverse so noiselessly that it is necessary to watch them closely to tell when the reversing occurs.

The line shafting in shops and mills can be connected up in sections by using magnetic clutches; and any section can be instantaneously disconnected by snapping a switch located anywhere in the shop, or from any one of a number of points, as might be desired.

Magnetic clutches can be so arranged in connection with counter-shafts that, instead of using a belt shifter, a small switch fastened to the machine is all that the operator will have to move. By this arrangement the counter-shaft does not have to be located directly over the machine, as is the common practice at pres

ent.

This system of clutches is almost ideal for use in cotton or woolen mills, where it is absolutely necessary to stop a loom instantly should a thread break in the weaving.

It requires very little force, and but an instant of time, to set or release a mag