Stránka:roll 1917.djvu/156

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124 Woodcraft Manual for Boys porcelain insulator and the latter is in turn fastened with a bit of wire to a spreader, that is a strip of wood one inch thick, three inches wide, and four feet long. Each spreader is then fastened to a strain insulator as shown at C 1n Fig.1 when the aiérial 15 hoisted and fixed to the supports; and don’ t forget that the higher the aérial and the longer the wires the greater the distance to which messages can be sent and received. The Ground Next in importance to a high, long, and well-insulated aiérial is the ground, and there are several ways of getting a pretty good one. The first way is to use the gas or water pipes and to solder a No. 6 bare copper wire to it, or ,fasten it on with a ground clamp; another way is to drive a piece of iron pipe into the ground deep enough to reach moist earth, but the best way of all 15 to solder a copper wire to a sheet of copper, or zinc, three I I feet wide and four feet long and bury 1t deep into the moist earth. nqz LIGHTNING swam To make an 38ml 3 safety de evice rather than a source of danger from lightning it should be grounded, when you are not sending or receiving, through an aérial switch as shown in Fig. 2. This switch is screwed to the outside of/your operating room near the window where the atrial and ground wires go through to the inside. ,ro INSTRUMENTS / wuvoow 7V/HJV 01 Gil/7089 0.1 The Sending Apparatus To send messages you will need the following pieces of ap— paratus: (I) an induction coil, or better a transformer, (2) a telegraph key, (3) a spark-gap, (4) a battery, or if your house is wired you can tap the circuit and get your current from that source, (5) a tuning coil, and (6) a condenser. THE INDUCTION C011,, on TRANSFORMER. The purpose of an in- duction coil is to change the direct current of a battery or lighting circuit into high pressure alternating currents. A transformer is used where alternating current only can be had. A transformer is better and cheaper than an induction coil, having the same .4)..A..J.__ __.4'_. __-«__ #4.. u... L.