Nikola Tesla Books
LARGE TESLA AND OUDIN COILS 209 turning the cylinder in the same direction. In order to maintain the space between turns a loop of cord is passed over the cylinder and a weight hung from its lower point. The turn of cord, which should be heavy and approximately inch thick, will guide each succeeding turn, spacing them with fair accuracy. An experimenter who has built a set of apparatus recently from the author's directions, advises that he was able to straighten up the entire winding by running a metal comb along the wire as an assistant turned the cylinder. The winding, when finished, is given half a dozen coats of shellac, each coat being dried thoroughly before the next is applied. The construction of the helix forming the primary will readily be understood from the drawings. The conductor is a length of ½-inch copper tubing, rubbed bright, and coiled into a helix 27½ inches in diameter for the Tesla coil and 26 inches in diameter for the resonator. A material superior to the tubing is the edgewise-wound copper strip that is now used in nearly all high grade wireless transmitters. This strip can be purchased in a spiral from any large wire manufacturer, but to bend it edgewise without buckling is a mechanical problem worthy of an engineer. It can be done by rigging up a drum of metal arranged with clamps to hold the strip flat as it comes from the reel, but the task is scarcely one within the province of the amateur. The Tesla coil is mounted upon a base equipped with casters in order that it may be moved quickly and easily. The secondary is supported by four rods of wood which are mounted in wooden bases in imitation of high tension insulators. The secondary is removable from the supporting rods merely by lifting it off, the rods terminating in plugs which fit sockets in the heads of the cylinder. The rods themselves are removable from the base by lifting
