** Home-Made Soldering Clamps [137]

Take a cotter pin and bend it over a small rod to bring the points together, as shown in the sketch.  This will make a spring clamp that is opened to slip over the articles to be clamped together by inserting a scratch awl or scriber between the legs at the bowed portion.  To make a more positive clamp before bending the legs to a bow, slip a short coil of wire over the pin, passing it down to the ring end.  Wire 1/32 in. in diameter wound over a wire slightly larger in diameter than that of the cotter will do.  In soldering, smoke the legs well to avoid solder adhering to them.  The clamp is tightened by pushing up the coil ring toward the bow of the legs and then twisting it like a nut, the coil being wound right-handed, so that it will have a screw effect.

[Illustration:  Clamp]

** A Telephone Experiment [137]

If the small apparatus, as shown in the accompanying sketch, is attached to the under side of an ordinary dining table, it will, if connected to a telephone circuit, set the table in vibration, so that any number of people who put their ears flat upon the table will hear the voice of a person speaking from a distance, apparently coming out of the table, says the Model Engineer.  A small piece of wood, A, Fig. 1, is cut about 5 in. square, to the center of which is attached a small piece of soft iron wire, such as used for cores

[Illustration:  Mechanical Table Talk]

of induction coils, about 4 in. long and bent in the form of a hook at the lower end, as shown at B. This wire is attached to the block of wood, A, as shown in Fig. 2.  The end of the wire is soldered to a small brass plate which is set in the block so it will be level or flush with the top of the block and then fastened with two screws.  The block A is fastened to the under side of the table with two screws.  A small coil, C, is made by winding No. 24 silk or cotton covered wire around a small tube, either a piece of glass, a short straw or a quill.  The coil is made tapering as shown without using wood ends.  This coil is slipped over the wire B previous to soldering it to the small brass plate.  The ends of the coil are connected to two binding-posts which are fastened to the block A. A small lead weight weighing 2 or 3 oz. is hung on the hook made in the lower end of the wire B.

When all connections are made, as shown in Fig. 1, and the block fastened to the under side of the table, the apparatus is ready for use, and has only to be connected to an ordinary telephone transmitter and batteries as shown.  The apparatus will work to a certain extent even if the weight is removed, though not so clear.

** Wax Wood Screws [137]

Some workmen use tallow on lag or wood screws.  Try beeswax for this purpose.  It is much cleaner to use and is just as good if not better.

** How to Make an Induction Coil [138]