. St. Nicholas [serial] . 16. FIG. 17. DETAILS OF CIRCULAR PUSH-BUTTON. strip, Fig. 17), fast to the door, or window-casingafter the wires are in place; the button is thenset in the hole, and the cover placed over thebase, and by means of small screws passedthrough the rim of the box and into the edge ofthe base the cap is held in place. ELECTRO-MAGNETS. The familiar horseshoe magnet is made ofhighly tempered steel and magnetized so thatone end is a north pole, the other a south, orperhaps more commonly known as a negativeand a positive. Once magnetized, it is alwaysmagnetic unless the power i
. St. Nicholas [serial] . 16. FIG. 17. DETAILS OF CIRCULAR PUSH-BUTTON. strip, Fig. 17), fast to the door, or window-casingafter the wires are in place; the button is thenset in the hole, and the cover placed over thebase, and by means of small screws passedthrough the rim of the box and into the edge ofthe base the cap is held in place. ELECTRO-MAGNETS. The familiar horseshoe magnet is made ofhighly tempered steel and magnetized so thatone end is a north pole, the other a south, orperhaps more commonly known as a negativeand a positive. Once magnetized, it is alwaysmagnetic unless the power is drawn from it byexposure to intense heat. An electro-magnet,however, can be made from any scrap of softiron, from a piece of ordinary telegraph-wire toa gigantic iron shaft. When a current of electricity passes through. A SIMPLE ELECTRO-MAGNET. an insulated wire coiled about a soft-iron objectsuchas anaiLabolt, orarod,that object becomesa magnet as long as a current of electricity ispassing through the coils of wire or helix. Acoil of wire in the form of a spiral spring has astronger field than a straight wire carrying thesame current, for each turn or convolution addsits magnetic field to that of the other turns ; andby having the center of the coil of iron, whichis a magnetic body, the strength of the magnet-ism is greatly increased. A very simple form of electro-magnet is made 1905] THE PRACTICAL BOY, I I I 7 by winding several layers of No. 20 insulatedcopper wire around a stout nail or a carriage-bolt; and, by connecting the ends to a batteryof sufficient power, some very heavy objects canbe lifted. A single-magnet, like the one shownin Fig. 18, and C in Fig. 19, is made with apiece of soft-iron rod 6 inches long and halfan inch in diameter, the ends of a large spoolsawed off and worked on the r
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Keywords: ., bookauthordodgemar, bookcentury1800, bookdecade1870, bookyear1873
