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merely going up hill and down hill, the track is constructed at one point so that the car goes vertically around a perfect circle in the air. It gets such a headway from going down a steep incline that it turns a complete somersault as a result of its own velocity. The motion, however, is so rapid that persons in the car do not fall out but are held in their places by the effect of centrifugal force. As will be noted, the photograph shows the car at the very top of the "wheel," while the passengers in it are actually suspended for the moment with their heads downward.

Photos in the Subway MOVING pictures of the loading and unloading of trains and of their operation in the New York subway were

recently taken by the light of a whole. car-load of Cooper-Hewitt mercuryvapor arc lights. For the purpose of these photographs seventy-two mercuryvapor lamps, each of 750 candle-power, were mounted on a couple of flat cars, which ran through the subway just in advance of the car carrying the camera and operator, and immediately behind. the train which was to be photographed while it or its passengers were in motion. The great banks of lamps were arranged. diagonally across the flat cars, so that the light was thrown immediately ahead and along one side of the tunnel. The time of exposure was seven minutes and during that time about 6,300 pictures were taken, the camera operating at the rate of about 900 pictures a minute.

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Machinery to Roll Glass AN invention for drawing molten glass out of the furnaces and rolling it mechanically, has been sold to a syndicate of plate glass manufacturers for $952,000. The inventor is a Belgian, Mr. Fourcault, and the purchasers of his patent rights are German, French, Belgian and Bohemian manufacturers. Only high priced manual labor has been able to do this work heretofore. In making window glass the viscid glass was drawn out from the furnaces and blown into cylinders by men, and with plate glass the hot molten mass was cast from pots and rolled to the desired thickness. The new mechanical process is, of course, much cheaper and quicker. The machine brings the liquid glass from the pots and draws it between rollers, seventeen pairs

of which tower above the pot. The mass of hot glass gradually cools as it passes

MERCURY VAPOR LAMPS FOR PHOTOGRAPHING THE NEW YORK SUBWAY.

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Built for Chicago Terminal Transit Railroad by Chicago Bridge & Iron Works. Length, 115 ft. 5 in., depth, 10 ft.

ered a method of shipping fish without water, based on the fact that they will live five or six days out of their native element if their gills are kept wet, and they get the required amount of oxygen. Under the new plan the fish are placed in a tightly sealed shipping box, containing water soaked cloths. These cloths keep the air saturated with moisture, and the oxygen is supplied by pumping it through a tube into the box.

Enormous Plate Gird

ers

STEEL GIRDERS of enormous size

are employed in the new construction work being done by the Chicago Terminal & Transfer Company. They are among the largest ever manufactured for railroad purposes. All the structural iron employed in the work was made by the Chicago Bridge & Iron Works, and the huge proportions of many of the

Constructions of almost equal size have recently been made by the company for use in improvements on the Northern Pacific, the Santa Fé, the Chicago Burlington & Quincy, and other railroads. The size and weight of the girders which can now be manufactured in Chicago is limited only by the ability of the railroad companies to transport them.

Sunflowers for Profit

ONE hundred acres planted with sun

flowers. A farmer in southern Indiana is raising sun flowers for profit. It is the seed, of course, which he sells. These seeds are pressed for the oil and then ground up into medicine for cattle and hogs. The oil is sold as "olive oil." The seeds now sell at 2c a pound in Indiana, and farmer McDonald figures a profit of about fifty dollars an acre on his farm. The seed runs about thirtytwo pounds to the bushel.

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Are you worried by any question in Engineering or the Mechanic Arts? Put the question into writing and mail it to the Consulting Department, TECHNICAL WORLD MAGAZINE. We have made arrangements with the American School of Correspondence to have all such questions answered by members of its staff of Instructors. If the question asked is of general interest, the answer will be published in the magazine. If of only personal interest, the answer will be sent by mail, provided a stamped and addressed envelope is enclosed with the question. Requests for information as to where desired articles can be purchased will also be cheerfully answered.

Blind-Nailing

What is meant by blind-nailing a floor?C. H.

A new method of matching boards. for nailless flooring is shown in the figure. This new arrangement of the tongue and groove gives more strength to the joint and is more accessible in driving the nails. This is a great im

BLIND NAILING A FLOOR.

provement over the old method as it is air-tight, dust-proof, and prevents drafts and the penetration of foul gases. The old method of keeping the heads of the nails out of sight was to simply toe them in from one edge, but this allowed the flooring to warp and become uneven. The tonguing of one edge and grooving the other, as shown in the figure, gives sufficient strength to the joint to hold the floor by blind nailing, making it selfsustaining.

Cleaning Castings

How are castings cleaned?-R. S. M.

After the castings have been poured, the sand is usually shaken off from the heavier parts, so as to produce an even cooling. The pouring is usually done at the close of a day's work. When the sand is shaken off, the sprues are broken from the casting by the blow of a hammer. The cleaning is done the next morning. This consists in removing the sand that may adhere to the surface of the castings, and taking the cores from the inside. There are three methods of removing the sand: by rattling, by brushing and by the sand blast. The first is used for small castings. They are put into a cylindrical shell, which is slowly revolved. The castings are thus tumbled over each other. As they rub and strike together, the sand is removed and the surface of the castings made smooth and bright.

The brush is made of strong steel bristles. These remove the sand from the surface of the casting. The brushes may be used by hand or be driven by power. This is the most common method of cleaning castings.

The sand blast is used upon heavy castings. It consists of cutting off the adhering sand by a stream of sand impelled by a current of air. Care must be exercised in using the sand blast as

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In brazing, however, the brass acts in joining two pieces of metal together in somewhat the same manner that glue does in joining two pieces of wood. Briefly the process is as follows: The surfaces to be joined are cleaned, held. together by a suitable clamp, heated to the temperature of melting brass, flux added, and the brass melted into the joint. The brass used is generally in the shape of "spelter" though brass wire or strips of rolled brass are sometimes used in place of spelter, brass wire in particular being very convenient in many places. A simple example of a brazed

(one part salammoniac, six or eight parts borax) which may be added dry or put on in the form of a paste mixed with water. The joint is then heated and the spelter mixed with flux sprinkled on and melted into place. Brass wire could be used in place of the spelter in the manner indicated, the wire being bent into a ring and laid round the joint as shown. Ordinary borax may be used as a flux, although not as good as the mixture used above. The heat should be gradually raised until the brass melts and runs all around and into the joint, when the piece should be lifted from the fire and thoroughly cleaned, by scraping off the melted borax and scale. It is necessary to remove the borax, as it leaves a hard, glassy scale which is particularly disagreeable if any filing or finishing has to be done to the joint. This scale may be loosened by plunging the work, while still red-hot, into cold water. Almost any metal which will stand the heat, may be brazed.

Ferrets to Lay Wires

I have read in the newspapers that ferrets are sometimes used to string wires through conduits. Is it only a newspaper yarn?B. W. A.

NEW WAY OF LAYING WIRES.

Ferret is made to lay the wires by attaching a light fish line to him and letting him chase a rat through the pipes.

joint is shown in Fig. 1, where a flange is brazed to the end of a small pipe. It is not necessary in this case to use any clamps as the pieces will hold themselves together. The joint between the two should be made roughly. If a tight joint be used there will be no chance for the brass to run in. The joint should fit in spots but not all around. Before putting the two pieces together, the surfaces to be joined should be cleaned free from loose dirt and scale. When ready for brazing the joint is smeared with a flux

The use of ferrets to lay wires is a practical expedient, according to Mr. Cline, Superintendent of the Bell Telephone Co. at Terre Haute, Ind. He says it is the best way to get wire through ducts. A little harness is made for the animal and a light fish line attached. Then a rat is turned loose in the duct and the ferret leads him a merry chase through the conduit until he reaches the next opening, when the rat falls into a bag or trap. But in the meantime the ferret has carried the line through the

pipe and the hardest part of the work is over. If the ferret should catch the rat he would eat him and then go on a strike, for it is only hunger that makes him. work, so that is the reason why the rat must run into a bag and not get caught. According to Mr. Cline a ferret will do the work of three men in laying wires.

To Set Compound Gears How are compound gears set?-L. R. G.

To set compound gears divide the number of threads per inch to be cut by the number of threads per inch on the lead screw. The quotient will be the proportional number.

COMPOUND GEAR.

Select a gear for mandrel, and also one for smaller wheel of compounded pair, and multiply them together, then multiply the product thus found by the proportional number.

Select another gear for larger wheel of compounded pair and divide it into the above product, and the quotient will

give the wheel to be placed upon the lead screw. Judgment must be used in selecting the mandrel wheel and wheels of compounded pair, as the thread to be cut is either coarser or finer than pitch of lead screw.

Automobile Troubles

1. What is the cause of "back firing" in gasoline engines?

2. What causes the piston to smoke?——— L. V. R.

1. This trouble is of most frequent occurrence with fuel of a low ignition temperature, such as gases rich in hydrogen, and gasoline. If the ignition apparatus is properly adjusted, the source of the trouble may be traced to an overheated cylinder and too high compression, or to highly heated projections within the compression space. The latter cause of this annoying trouble has frequently been a puzzle for some of the best gas-engine men to find. A thin projection of metal within the cylinder may be so situated that it becomes heated to a comparatively high temperature and acts in the same manner as an ignition tube. Again, there may be a projection within the cylinder upon which carbon will deposit in the shape of a cone. This cone of carbon will become incandescent, or nearly so, and cause premature ignition, even as early as on the suction stroke. Projections upon the piston head such as the heads of follower-bolts, nuts, etc., quite frequently make trouble. in this way. In two-cycle engines of the Day type, explosions will sometimes occur in the crank-chamber because of an insufficient fuel supply.

2. In this case the piston is leaking. The remedy will suggest itself, upon taking out the piston and examining its condition. If the cylinder is badly out of round it should be rebored. The packing rings may need renewing. See if they are too small to expand to a size slightly greater than the bore of the cylinder. Smoke from the open end of the cylinder may also come from overheating. Smoke issuing from the exhaustpipe, is due to an excess of fuel in the mixture.

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