Nikola Tesla Books
PHYSICIANS' OFFICE EQUIPMENT 125 over the core. A single turn of micanite is placed between layers of wire to insulate the winding and to keep the latter uniform. A convenient method of making the taps in the primary is to solder a length of copper ribbon to the proper turn, insulating the ribbon thoroughly with paper where it passes between adjacent turns. To this tap of copper strip, a flexible stranded cable may be soldered and carried to the switch on the outside of the transformer case. When the primary winding is finished it may be given several coats of armalac and permitted to dry. The secondary is wound in two sections upon the other leg of the core. Each section has 4.200 turns of No. 28 enameled wire which is wound in layers 1 in. wide with layers of oiled paper 1½ in. wide, between. The precise manner in which this winding is done has been covered so thoroughly in other chapters of this book that to reiterate the instructions would be superfluous. When the windings have been completed, the core is assembled by fitting in the longer core pieces in the spaces left between the projecting ends of the cores containing the windings. This is rather a tedious job, but with the aid of a small hammer judiciously applied, the magnetic circuit may be completed without undue labor. The magnetic leakage tongue is wedged between the yokes of the core by means of wooden strips. The complete transformer is mounted within a wooden case, the dimensions of which have not been given. The Rotary Spark Gap.-This gap may be of the stock variety sold by many wireless supply houses for use in connection with amateur transmitting sets of from onehalf to one K. W. capacity. The design presented in Fig. 1, however, is simple of construction and in use it will be found superior to some of the manufacturerd articles now on the market.
