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goes to bed! Or for the lawyer in a city court room to see the face of

prospective witness fifty miles distant the while he talks with him over the 'phone!

And these things are but hints of the multitudinous possibilities of a machine that will enable you to see for business and household needs to the same extent practically that the telephone enables you to hear.

44 PHOTOGRAPH TAKEN THROUGH TELESCOPE SYSTEM."

Dudley's idea has been to develop the contrivance by which, years ago, you went to a county fair and in a tencent "side show" "saw through a brick," that is, a square tube in the form of a half-square was fitted around a common paving brick. At the angles were fitted slanting mirrors. You peered in at one opening and the rays of light coming in at the other opening were deflected by the two mirrors so that you literally saw what was on the other side of the opaque brick.

The person photographed was several hundred feet away from camera, and out of ordinary sight.

The inventor calls his device the "United Telescope and Telephone System" or house to house telescope system. But the name is the poorest part of his invention and gives little idea of the possibilities of the thing.

Dudley's training for inventing has been long and thorough. He worked for a number of years in the railroad shops at St. Paul and is a practical machinist in every way. It was Dana Dudley, it is asserted, who invented the dynamite gun which is now used on every torpedo boat. This was in 1889. has now a $26,000 suit pending in the Federal courts over his claim on royalties from the dynamite gun invention.

He

So effective is the seeing-through-abrick device that one may easily photo

graph a person who is many hundreds of feet or rods away, out of ordinary sight and on a floor or elevation hundreds of feet higher or lower than the person operating the camera. Another valuable development feature is that by the use of ordinary artificial light at each receiver the operator can get better results even than with daylight. Thus, a private watchman could thoroughly inspect a great factory by simply using the receiver of one of these seeing-through-abrick machines in his bunk room, turning on the electric bulbs for each floor and each room.

The test of an invention is: Is there a need for it and will it work? Dana Dudley's telescope scheme answers "Yes" to these two questions. Just as the telephone has been improved and adapted by myriads of switches and contrivances for numberless needs and uses, it is entirely probable that the seeingthrough-a-brick idea will be so developed.

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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 to have all such questions answered by a staff of consulting engineers and other experts whose services have been specially enlisted for that purpose. 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.

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I have a small incandescent lamp which I am operating from three dry cells in series. After using these cells for two or three weeks, the light grows dim, although the cells do not seem to be exhausted. Can you suggest á remedy for this?-A. E.

The accompanying sketch shows five dry cells connected in such a manner that by means of a three point switch the lamp may be placed in series with three cells, four cells or five cells. As the original three cells weaken, it will be found necessary to place another cell in series to keep the voltage high enough for satisfactory operation of the lamp. This cell

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in turn will weaken and you will still have the fifth cell to throw in series. In this manner the original three cells may be worked until they are practically exhausted before being thrown away. If you were operating your lamp continuously for any great length of time, the use of dry cells would not be advisable, as they are not suited for this kind of service.

Waterproof Glue

I should be pleased to have you print a formula for making a good waterproof glue.T. A. J.

Dissolve separately in ether, under the influence of a gentle heat three parts gum shellac and one part india rubber by weight. Mix the two together, after dissolution, and seal for a time in an airtight vessel. When ready for use, the glue will be found to resist the action of water, both hot and cold, as well as of most acids and alkalies. If ether is mixed with the glue, it may be applied to leather as a varnish along the seams where they have been sewn together, and gives a waterproof surface.

Handling Hot Main Bearing

1. How should a hot main bearing be handled?

2. What kind of lubricant is used for ordinary machinery, for valves and pistons, and for high and slow speed engine bearings?-S. C.

The first thing to do is to start your oil feeding as rapidly as possible, then slacken off the set screws or wedges, applying the oil freely, mingled with a little water. If the bearing becomes "smoking" hot, slow the engine down, but keep "her" "turning over." If the bearing begins to cool off and the babbitt has not run, you may speed up the engine to full speed with safety, but keeping a close watch on the bearing until you are satisfied that it is back to its normal condition again.

Don't slacken off the set screws or wedges too much, for an engine will pound itself hot if the bearings are too loose.

If the babbitt has run badly, it will be necessary to jack up the shaft, take out the shells, have them re-babbitted, bored and scraped to a true surface, in the same manner as crank pin brasses are ordinarily handled.

To handle a hot main bearing is a simple matter in comparison with a hot crank pin, because one can usually slacken off the set screws or wedges, while the engine is in motion, so as to make it run loosely and enable you to keep the engine in motion.

2. For ordinary machinery use mineral, vegetable or lard oil. For valves and pistons use heavy mineral high test oils and little graphite. For engine bearings use castor, sperm or some heavy mineral oil.

Joining Band Saws

Please give directions for joining small band saws.-A. F. W.

The parts to be joined must be beveled to a nice fit. Secure the saw at both ends in clamps. See that the edges are parallel, or a short and a long edge will be the result, which will cause the saw to run badly and to break on the short edge when strained. Put on the filed parts a thin coat of borax paste. Cut a piece of very thin sheet silver solder of the same size as the joint to be made, which place between the lap. Take a pair of tongs

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hold the joint with the hot tongs until the solder has thoroughly melted; remove the hot tongs carefully and follow up with another pair heated to show a dull red, which will set the solder and prevent the joint from being chilled too suddenly. The joint can then be dressed to the thickness of the saw blade. It would be as well to have a pair of cold tongs to clamp the hot jaws firmly to the joint, as the hot iron must fit nicely over the whole width of the saw. In joining, do not make the lap longer than is absolutely necessary.

A Seed-Corn Rack

I should like to have you make a diagram, or give a description of a rack for storing seedcorn.-H. G. H.

The following method has been suggested by Mr. G. I. Christie of the Purdue University Experiment Station: To secure a thorough circulation of pure air, corn after being picked should be hung

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Watch as Compass Can a watch be used as a compass, and how?-H.L.B.

Due south can be readily ascertained if one possesses a fairly correct watch and the position of the sun is distinguishable. Point the hour hand to the sun, and the south is exactly half-way between the hour and the figure XII on the watch. For instance, .suppose that it is 4 o'clock. Point the hand indicating IV to the sun and II on the watch is exactly south. Suppose that it is 8 o'clock, point the hand indicating VIII to the sun, and the figure X on the watch is due south.

be out of range of the sun's rays. The rack here illustrated will render satisfactory service for storing the corn when dried.

Draining a Gellar

How can I drain a Cellar?-B. L. E. In the sides of a box, about an inch from the bottom, a row of holes should be bored. The box should be connected with an ordinary steam syphon, as shown in the illustration. The function of the holes is to allow the subsoil water to enter. When a sufficient quantity has accumulated it will be drawn off by the syphon, which is controlled by a float through valve B. A bracket, D, supports the float. This bracket is attached to the steam pipe and can easily be constructed out of an old tin can, and when it rusts out can speedily be renewed. In place of steam, water under pressure may be used.

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To Make an Ash Sifter

Please describe an ash sifter that can be made at home.-E. L. R.

A wire sieve (already woven) can be bought at any hardware store. It may be tacked to a frame made to fit the sifter, one end just reaching over the box for

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lows: To a piece of 3%-inch pine, 41⁄2 inches wide and 6 inches long, glue, on each end, a strip of similar material onehalf inch wide. Next take a piece 41⁄2 inches wide and of sufficient length to fit closely between the two 2-inch strips. Take a piece of felt and on the wood, as indicated in the illustration, glue on the side opposite that to which the strips are glued. Then take your sand paper and fasten in place by pressing the 42 by 6-inch piece between the strips.

Drilling vs. Punching Rivet Holes Which is the better practice, to drill or to punch rivet holes in boiler-shells?-T. R. A.

In boiler-shell work, drilling has entirely displaced punching,, and today all holes are drilled. Punching is cheaper than drilling, but it is more injurious to the plates and not as accurate. It is easy to see that drilling rivet holes, even if twenty are being drilled at once, is done with less strain on the plates than when done by a multiple punch forcing several holes at once. The force required to punch a plate gives the best idea of the harm done to the plate. Experiment shows that the resistance of a plate to punching is about the same as its resistance to tensile tearing. Suppose this to be 50,000 pounds per square inch; then the force required to punch the plate is the area cut out times the shearing strength, or d xx tx 50,000.

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If the force required to punch one hole is 58,900 pounds, the force required in punching several holes by means of a multiple punch is enormous.

A good, ductile plate is but little injured by punching; but if of a hard, steely nature, it is likely to be seriously. injured. For this reason, wrought-iron plates are usually punched and steel plates are drilled. On the whole, a drilled plate is somewhat stronger than a punched plate for any kind of joint.

Some boiler makers punch the rivet. holes slightly smaller than the desired. size and then ream them out. By this process the injured metal around the holes is cut away.

To Smooth a Painting

Can a painting, whose surface bulges out in places, but which is not cracked or broken, be smoothed?-T. R. R.

The best way, probably, to remove the inequalities referred to, is to wet the canvas on both sides and keep it under pressure till dry. If the picture is small, take it off the stretcher and lay it in press, under light pressure, with soft sheets of paper intervening.

Portable Saw Horse

I should like to have you print directions for the construction of a portable saw horse such as carpenters use.-E. J. C.

The accompanying illustration will give a better idea of how such a saw horse may be made than a verbal description can give. The whole is quite simple. and will be readily understood by any carpenter, at a glance.

PORTABLE SAW HORSE.

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