Nikola Tesla Books
208 HIGH FREQUENCY APPARATUS the projecting corners and a final rubbing with coarse sandpaper will bring the surface to a fairly smooth condition. The winding surface is prepared by covering the cylinder with several layers of heavy wrapping paper, each layer being thoroughly soaked with shellac before the next is applied. The easiest and best way to do this is to purchase a roll of paper and place it in hangers beside the cylinder. The Tesla secondary may be wound in two sections with a space between at the centre of the coil. This space will provide for the legs that support the primary helix as shown in the drawings. The wrapping paper need therefore be only half the length of the cylinder in width in order to fully serve the purpose. When the cylinder is covered and the paper and shellac have dried quite hard, the winding may be done. The exact size of the wire on the Tesla secondary is of small importance. The only requisite is that the number of turns be kept between 600 and 800. There should be an appreciable space between each turn and its neighbor, however, and this may govern the gauge of the wire employed. It is difficult to secure any wire larger than No. 22 in a length sufficient to wind the cylinder in one piece and a splice is not to be desired. If, therefore, No. 22 B. & S. gauge, double cotton covered magnet wire is available, it may be wound 12 turns to the inch, making in the neighborhood of 300 turns in each half of the winding. The two halves of the winding must be in the same direction; that is to say, the one half is a continuation of the other. This is easily assured by starting at the left end of the cylinder, for instance, and winding until within 1½ inches of the centre. Here the wire is secured with a wooden peg and a jump taken over 1½ inches to the other side of the centre of the cylinder. Another peg secures the starting turn and the second half of the winding is completed,
