Baron Karl von Reichenbach                    

Reichenbach found that some people that could not sleep and were "sensitive" could perceive a glowing of objects in a room which was totally absent of light.
He tested many subjects and was surprised to find they all desribed similar behavour of a type of flame, glowing or light radiated from many objects such as crystals, magnets and electricity.
He conducted many years of research determining the characteristics of this odic energy, determining that it is quite different from electricity and magnetism, behaving quite differently, though always consistently, as described by many sensitives.
Despite Reichenbach never being able to see any of this glowing behavour, he found very similar descriptions and behavour from sensitives reporting. This included being able to inform him of events in pitch blackness such as whether electricity was turned on or off in a wire.
  Horse shoe and bar magnets as described by sensitives, glowing and with flames on the ends. More bluish on the north pole and more reddish on the south. Magnets are often painted these same colours.  

His compiled research is presented in a pdf book called:

Researches on Magnetism, Electricity, Heat, Light, Crystallization and Chemical Attraction in Relation to the Vital Force