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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 wil 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.

To Make Handy Truck Can you suggest how to construct a cheap, .handy truck for moving timbers, stoves, etc.

The incline should be very slight.-H. M. K.

Starting with the contact-breaker, which is grounded, the circuit passes to the single-pole double-throw switch ; then through one of the sets of batteries, depending upon the position of the switch. The wires from the batteries unite, and pass to one side of the primary of the spark coil. The other side of the primary is grounded, the circuit being completed 'to the contact-breaker in this manner. One secondary wire passes to one terminal of the spark plug, which is insulated from the plug itself. The other sec

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Turn a roller 4 inches in diameter and 12 inches long. Through this, bore a hole for the axle, about 34 inch in diameter. Take two side pieces, as shown in the drawing, cut from a single 2-by-4inch plank, and at the angle indicated. For the top, nail on boards 16 inches wide, and an inch thick. The truck need be no longer than 18 or 20 inches. A 34-inch piece of round steel or iron should be used for the axle.

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Wiring for Spark-Coil How would you wire two sets of batteries for an automobile runabout so that either set could be thrown into service by means of a switch ?-H. W. S.

A simple way of doing this is shown in the accompanying sketch. The circuit may be traced out as follows:

SWITCH

WIRING FOR Two SETS OF BATTERIES.

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How to. Ventilate a Barn Can you tell me how to ventilate a barn without common roof ventilators, as the sparrows render them a nuisance?—G. M. J.

A screen over the opening of the ventilator should obviate this trouble. To remove the atmosphere from the barn itself, the illustration will best show the method. Board up the space between two studdings. Clear the plate-box out at the cornice, and finish with turret effect on

Screen

Copper con 7 on to Tin

Gun metal
Bell metal
Bronze coin

95

1 Phosphor bronze 92727

Yo Phosphorus Manganese bronze 89 10

1 Manganese Aluminum bronze 90

10 Aluminum Valve metal (best) 88 10 2 Valve metal

183

15 Bearing metal

77

15 Trace of Phos

phorus Brass (common) 166%

333 Muntz metal

160

40 Delta metal

56 42

2 Iron Brazing metal (soft) 50 12% 37% Brazing metal (medium)

50 50 Brazing metal (hard) 75

25 German silver

60
20

20 Nickel Fusible plug

10

86 4 Bismuth Common solder

50

50 Fine solder

6633 333 Babbitt's metal

3 89

8 Antimony Babbitt's metal

80

20 Antimony Pewter

80

18 2 Antimony Britannia metal

90

10 Antimony Type metal

80 20 Antimony Regulus metal

88 12 Antimony

Open in warm weather

Vent Closed when upper vent is open.

METHOD OF VENTILATING A Barn. Noisy Telephone When you hold the open end of the receiver the roof. Screen openings should be proclose to the transmitter of a telephone, why

vided on all sides. Slide shutters should do you hear a loud, shrill hum?-H. E.

be used for the interior openings. This does not always take place; but when it does, it is due to the following action:

Pipes over Batteries •If the diaphragm of the transmitter is Why should no metal pipes be run above of iron, then, when the receiver is

a storage battery?-F. H. T. brought near it, the permanent magnets If metal pipes are placed above a storin the receiver will attract the transmit- age battery, the fumes arising from the ter diaphragm. This will alter the resist- solution come in contact with the metal. ance of the transmitter circuit of the A speedy corrosion of the pipes naturally phone, inducing a current in the sec- follows. Metal salts are formed in little ondary circuit, which will act upon the scales, which jarring is likely to shake receiver diaphragm, causing it to move. loose; and these, falling into the storage This motion of the receiver diaphragm cells, cause a very rapid deterioration of will react upon the transmitter dia- the plates. If, owing to the fact that pipes phragm; and consequently, if conditions already have been installed, it is inconare just right, there will be set up a vi- venient to dispense with them, they may be boxed in. It is better, however, to

Since PQ is perpendicular to angle A, angle run the pipes around instead of over the

HQP is a right angle. Likewise PRK is a

right angle. But angle HPQ = angle RPK, batteries. In boxing-in the pipes, a black

and PQ=PR. Then triangle HQP=triangle asphalt paint should be used on the wood, KPR, and HP= PK, and HQ=RK. Again, as asphalt is immune to the vapors. we saw that angle HPS = angle KPS. Then

triangle HPS = triangle KPS, having two

sides and the included angle of one equal to A Geometrical Theorem

two sides and the included angle of the other.

Therefore angle PSH = angle PSK, being If two equal adjacent dihedral angles are cut homologous angles of equal triangles. by any plane (not perpendicular to the common edge of the dihedral angles), the angles formed

For Leaking Roofs Will you please tell me how to construct a water spreader for roofs, so that water will not be concentrated at one point and leak through?—P. L. K.

We presume that the roof is of but slight pitch, as where the pitch is steep, and good slate or good shingles are used, a water spreader will not be necessary. The illustration shows the finished spreader in place. It should be made of copper or galvanized iron bent to the shape desired on any brake or bending machine. The width and length, of

course, will be governed by conditions. in that plane by the intersection of that plane with the faces of the dihedral angles, are equal. Please prove.-J. W. P.

If the cutting plane is passed through a line which is perpendicular to the edge of the dihedral angle, the problem admits of solution as follows:

Let PS be a line perpendicular to the edge AB. Pass the plane CPSD through PS, cutting LA in CS, and AM in SD.

Pass the plane TPR' through PS perpendicular to AB. Drop the perpendiculars PQ and PR to the planes LA and AM. Then PQ will equal PR. (All points in the plane which bisects a dihedral angle are equally distant from the faces.) The angle PSQ = angle PSR, these being the plane angles of equal dihedral angles. PS PS. The triangle POS, having the hypothenuse and acute angle in each equal, = triangle PSR; and QS=SR, being homologous sides, cutting CS in H, and SD in K, an forming the trihedral angles P-HQS and P-SRK. Dihedral angle H-SPQ = dihedral ngle R-SP-K, being vertical

The particular design here pictured dihedral angles.

Dıhedral angle S-PQ-H = dihedral angle spreads the water out in a thin sheet; K-RP-S, being right dihedral angles. moreover, it cannot suffer injury by ice

The angle OPS = angle SPR because of forming on it. The dimensions of the Trihedral angle P-HOS = trihedral angle spreader should be about 18 by 15 inches. P-SRK, having two dihedral angles and the

A little device of this sort will remedy included face angle of one equal to two dihe- the evil resulting from water working its dral angles and the included face angle of the way through the joints of shingles and other.

boards. The value of an aid of this sort Then angle HPQ = angle RPK, and angle HPS = angle SPK, being homologous face depends, of course, upon proper construcangles of equal trihedral angles.

tion and placing

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WATER SPREADER FOR Roof TOP.

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