Mounting locations should not be in the path of the rising arc. Connect the high tension output of the transformer to the two rods using high voltage insulated wire unless the routing is such that there is no chance of arcing where you don't want it. DO NOT use automotive ignition cable for this unless it is the non-resistive type. Depending on the voltage and power rating of your high voltage source, these dimensions may vary considerably. Spirals and other more creative configurations are also possible.
X is mount attachment.
Essential line fuse, power switch, and power indicator lamp not shown. A Jacob's Ladder works on the principle that the ionized air in the arc is a lower resistance than the air around it and heated air rises. The arc strikes at the point of lowest breakdown voltage - the small gap at the bottom. The heated plasma rises and even when it is an inch or more in width is an easier path for the current to follow. Eventually, the gap becomes too wide, the arc extinguishes and is reestablished at the bottom.