Nikola Tesla Books
186 HIGH FREQUENCY APPARATUS which makes contact with the brass bushing in the top of the cylinder. A wooden cone is turned up in imitation of a high tension insulator and the rod carrying the ball runs through the center of this cone. The construction of the primary coil and base will be understood on reference to Fig. 2, which gives a plan view looking down on the primary from the top and also a side elevation of the lower portion of the complete transformer in cross section. It will be noted that the primary is composed of nine turns of heavy copper ribbon two inches wide and wound in the form of a true spiral. The ribbon is wound into its finished form with a double thickness of inch rubber belting between turns. It is taped at three or four places to hold it in place temporarily while the supports are being constructed. The object of elevating the primary coil is to provide. means of access to the under side in order that connection may be made with any desired turn. The coil is gripped between pieces of fibre bar A which are held in place by fibre bolts B and the whole is supported on the elevating posts C of fibre. The base is of wood and it should be mounted upon four glass or porcelain insulators. The finish of the base is preferably of the same color as that used on the secondary cylinder; the black vegetable dye provides a finish that is rich and pleasing in appearance and at the same time rather unusual. If the copper primary ribbon is highly polished and lacquered, a pleasing contrast will result. A square wooden box is mounted upon the base and in its top is a short bolt threaded to enter the hole in the brass bushing in the lower end of the secondary cylinder. A strip of copper ribbon makes connection between the bolt and the inside turn of the primary spiral. Connection between the primary and the balance of the
