This term was first used by Baron von Reichenbach to denote the subtle effluence said to emanate from every substance in the universe (especially from the stars and the planets). It also emanates from humans, crystals and magnets. The odyle was believed to be perceived only by sensitives, and it would give them vague sensations of heat or cold. The extremely sensitive might sense the odyllic light, a clear flame with a definite colour which would issue from fingertips, magnetic poles and various metals and chemicals.
The colours were said to vary according to the substance, and Reichenbach's beliefs were tested using various sensitives with strong results in his favour. The public imagination was captured by the idea, and Braid - who was promoting his theory of suggestion around the same time was largely unheeded.