A geocurrent bridge is a megastructure (relative to the size of the Manifold Sky) used to harvest renewable electrical energy from the seasonal charge differential that develops between the Northern and Southern Tesseracts. Several geocurrent bridges have been constructed as of the year 10,000 AR, including the Grand Leyline in Voxelia, the Seastorm Thundersnare in the Rostran Archipelago Confederacy, and the Desert Transmission & Utility Trunk (also known as the Liberty Leyline) in the Free Faces League.
Purpose / Function
During the summer months, the Northern Tesseract and all adjacent cube layers develop a slightly positive charge due to ambient charged particle radiation from some source outside of the Manifold. This charge is most intense during the summer solstice, fades to neutral during the equinoxes, and becomes negative during the winter solstice. At all times, the Southern Tesseract maintains an opposite charge to that of the Northern Tesseract. This means that, when the Northern and Southern tesseracts are charged, a charge differential exists between them. A geocurrent bridge can be constructed between Northern- and Southern-associated cube layers to tap into this charge differential and use it to generate an electric current. Power from a geocurrent bridge can be used to supply seasonal peak power to nearby electrical grids or to pump water into reservoirs at the heads of electric dams to provide backup power year-round.
While most materials currently available in the Manifold are not strong enough to allow it, Auburn Aerotechnical engineers have suggested finding a way to extend collector towers all the way up to the inflection layers leading into the Northern and Southern tesseracts. This would get the collectors closer to the strong charges in these locales, increasing the output of geocurrent bridges. The engineers are considering possible ways to connect the collector towers via buoyed cables or some form of remote transmission directly from skystations, which would make these geocurrent bridge/skystation complexes among the first active structures in the Manifold.
A geocurrent bridge consists almost entirely of a long bundle of subterranean cables strung through the commissures of a tesseract until they reach endpoints in cube layers adjacent to the Northern and Southern Tesseracts respectively. At the northern and southern ends of these cables are tall "collector" towers, which raise antennae up into the air to be closer to the inflection layers leading to the Northern and Southern Tesseracts. Substations near the center of a geocurrent bridge tap into the line and convert the current there into forms more suitable for use by the power grid. Because geocurrent bridges are critical infrastructure nodes, nations which construct them must be careful to protect them from attack. Collector towers and substations are invariably flanked with defensive military emplacements and placed in difficult to access locations; however, the need for defense must be balanced with maintenance accessibility. Geocurrent bridges can theoretically be long enough to span every cube layer in a tesseract - providing easy access and distribution for all residents via substations - but this greatly increases the chances of breaks in the line due to attack, misadventures, or acts of nature.
The powerful seasonal charges built up by buried geocurrent bridges cans sometimes cause detectable interference in devices like radios and magnetic armillaries. This interference has associated geocurrent bridges in many cultures with the concept of leylines: alignments of geographical features and structures that have an aesthetic, spiritual, paranormal significance. The practice of tapping geocurrent bridge cables with induction coils to 'steal' power from apparently nowhere does little to dissuade this belief in those who don't have a firm grasp of electronics. Notably, ovinex (especially of Native extraction) are distressed by otherworldly sensations of 'wrongness' they report around where the cables are laid. It has been suggested for this reason that ovinex neurophysiology may include a little-explored magnetoperceptive sense, and, out of an abundance of caution for public safety, the Rostran Archipelago Confederacy has issued regulations stating that no new lines may be laid beneath predominantly ovinex territories.