Baron Karl von Reichenbach, a successful German chemist and industrialist who had already discovered several real chemical compounds, turned in the 1840s to investigating what he proposed was an entirely new natural force, which he named od (sometimes "odyle" in English), distinguishing it explicitly from electricity, magnetism, heat and light, though he described it as related to and perhaps underlying all of them. Reichenbach held that od radiated from magnets, crystals, chemical and organic processes, the sun and moon, and living human bodies, and that it possessed polarity, a positive pole and negative pole, comparable in structure though not identical to magnetism.
Because Reichenbach himself reported he could not perceive od directly, his research depended entirely on a group of self-described "sensitives," typically people he identified as nervous or unusually susceptible, who reported seeing od as faint colored light, usually blue at one pole and red or yellow at the other, when observing magnets and other objects in near-total darkness, conditions Reichenbach considered necessary for the effect to be visible. He published his results in a series of works through the 1840s and 1850s, including letters later collected in English as The Odic Force, presenting od as a serious rival research program to established physics rather than as a fringe curiosity.