Nikola Tesla Books
HIGH FREQUENCY PLANT CULTURE 169 back in the lathe. The builder is strongly advised to do all of the painting in the lathe, as the examination and turning of the cylinder is greatly facilitated thereby. The third coat may be the final one and it should be dried as thoroughly as the first and second. The secondary finished, the wooden heads may be removed and connection made with the terminal and base studs. This is easily accomplished if the ends of the wire are left long and passed through the holes in the heads with the studs fitting loosely. When the heads are replaced, the wires may be drawn taut and the nuts of the studs turned up to grip the bare wire. The heads may then be secured in place by plugging with wood dipped in shellac, the small holes drilled around both top and bottom of the cylinder. The base of the instrument is simple in construction, as is readily seen in the drawing. The method of supporting the primary strip, as well as the nature of the latter, will, however, bear some explanation. The copper strip is one-half inch wide and one-sixteenth inch thick and is wound edgewise into a helix having an internal diameter of 1034 inches. This helix material is also to be obtained in the size given and it can be purchased far more cheaply than it can be formed up by the amateur workman unless he has the necessary equipment for the bending operation. As this device is quite complicated, the space necessary for its description will not be taken here. The problem is to bend the thin strip edgewise and prevent it from buckling. Assuming that the builder has procured the helix material, eight complete turns of which are required, the attention may be directed to the posts which support the helix on the base and at the lower end of the secondary cylinder. From the detailed drawing in Fig. 20 the reader will note that four posts of black fibre rod, 24 inches high
