This extraordinary phenomenon, it is now generally known, has been completely elucidated through the discoveries of Von Reichenbach, to which, in a former letter, I had occasion to make allusion.
You are probably aware, that the individuals whose nerves Von Reichenbach found to be so sensitive to the proximity of crystals, magnets, &c., would, in the dark, see flames issuing from the same substances. Then, in the progress of his inquiries, Von Reichenbach found that chemical decomposition was a rich source of the new power he had discovered, by its action on the nerves. And being acquainted with the story of the ghost in Pfeffel's garden at Colmar, it occurred to him as not unlikely, that Billing had just been in the same condition with his own sensitive patients, and that graves very likely would present to all of them a luminous _aura_; and that thus the mystery might find a very simple explanation.
Accordingly, Miss Reichel, one of his most sensitive subjects, was taken at night to an extensive burying-ground, near Vienna, where many interments take place daily, and there were some thousand graves. The result did not disappoint Von Reichenbach's expectations. Whithersoever Miss Reichel turned her eyes, she saw masses of flame. This appearance manifested itself most about recent graves. About very old ones it was not visible. She described the appearance as resembling less bright flame than fiery vapour, something between fog and flame. In several instances, the light extended four feet in height above the ground. When Miss Reichel placed her hand in it, it seemed to her involved in a cloud of fire. When she stood in it, it came up to her throat. She expressed no alarm, being accustomed to the appearance.
The mystery has thus been entirely solved. For it is evident that the spectral character of the luminous apparition in the two instances I have narrated had been supplied by the imagination of the seers. So the superstition has vanished, leaving, as is usual, a very respectable truth behind it.
It is indeed a little unlucky for this new truth, which reveals either a new power in nature or an unexpected operation of familiar ones, that the phenomena which attest it are verifiable by a few only who are possessed of highly sensitive temperaments. And it is the use of the world to look upon these few as very suspicious subjects. This is unjust. Their evidence, the parties having otherwise a character for honesty, should be accepted with the same faith and the same distrust with which all evidence is to be viewed; with neither more nor less than in other cases. Nothing should be received in scientific inquiry which it is not compulsory on our understanding to believe. It is not a whit more difficult in these than in other cases to obtain inductive certainty. Nature is not here peculiarly coy or averse from being interrogated.