Page:Popular Science Monthly Volume 88.djvu/306

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��Popular Science Monthly

��are for binding posts. Each element has its own set of binding posts. The rea- son for this is that some experimenters

have a step down trans- former which would b(' suit- able for the lights but cannot be used in con- nection with the magnet.

No dimen- sions are giv- armature (H), 1), their size magnet used.

���Bearing iwint of semaphore arm Fig. 4. Diagram showing con

��struction of lamp

en for the spring (G), or projection arm (Fig depending on the size The spring (G) should be made of some spring metal, such as gcrman silver or phosphor bronze. The armature (H) is made of soft iron and the projection arm of aluminum. The spring and arm are riveted to the armature.

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���Fig. 5.

��Plan of arrangement of parts, with dimensions

��An angle arm (J), holds the lamp to the standard. It should be about i/V' wide and each arm about \" long.

The string (K) attached to the pro- jection arm is the means by which the semaphore arm is moved when the ar- mature is pulled down ])y the magnet. If a light lirass chain is used in place of the string, the appearance is more real- istic.

Fig. 7 shows the wiring diagram when used with one source of current. The key is a .strap key or push-button,

��placed at a distance from the semaphore. In Fig. 1, the arm is shown with the cur- rent passing through the magnet.

When completed and as- sembled, if the cover, base and lamp are painted black, the standard painted white and the semaphore arm painted red with two white stripes as showm it gives the semaphore a very realistic appearance.

The semaphore need not be entirely electric as the sema- phore arm can be constructed so that it will move with a lever instead of an electro- magnet. In such a case, its construction will be much simpler than when electricity is used.

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��Fig. 6

��Saving Time in Tracing a Design

NEARLY e\ery worker, from the lady embroiderer to the machine shop designer, at some time has use for a symmetrical design, yet they us- ually go to the trouble of drawing each side out, or tracing one side. A far quicker and easier way is to use the following draughtsman's method :

Draw one half of the design out on tracing paper, or any strong tissue paper. Fold this over on top of the blank half, being careful that the crease comes exactly along the center line of the whole design. With a silver half-dollar, pass over the top of all us- ing a rapid to-and-fro stroke. The de- sign is now^ reproduced perfectly on the other half of the paper. For this work the pencil should not be too hard, F or B, or a common Xo. 2.

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��Fig. 7. Wiring diagram when semaphore is operated with batteries

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