You have already succeeded, I dare say, by means of the distinctive marks I have given you, in finding out some of your acquaintance whom the characteristics fit, those whom I called sensitives. In point of fact it is not difficult to lay one's finger on them; they are to hand everywhere in great numbers. And if you cannot at once get hold of some in quite good health, then turn your attention to those who pass restless nights, who are always pulling the bedclothes about during their sleep, who talk, or even get out of bed while dreaming, are greatly troubled by passing attacks of sick headache, frequent sufferers from stomach-aches of short duration, complain of nervous depression, are not fond of large parties, and like keeping to a few friends, or even seek for solitude. All such people are, with few exceptions, of a more or less sensitive nature.

What I have recounted, however, only makes up the trivial aspect of the matter on which you are consulting me; as soon as our subject is laid on the touchstone of science, things of quite other importance come into view. Just procure a natural crystal, as big a one as you can get, say a gypsum spar two spans in length, a heavy spar, or a St. Gothard mountain crystal a foot long, and lay it horizontally over the corner of a table or the arm of a chair, so that both ends project unsupported. Now lead a "sensitive" person up to it, and tell him to put the palm of his left hand within three, four, or six inches' distance from each end of the crystal, one end after

the other; it will not be half a minute before he will tell you that a fine, cool current is coming against his hand from the end of the upper part of the peak of the crystal, while from the other end—but on the lower, broken surface, that on which the crystal grew—a certain feeling of lukewarmness reaches his hand. He will find the feeling of coolness pleasant and refreshing, that of the lukewarmness unpleasant, and accompanied by a disagreeable feeling, one almost of disgust, which, after a short period, will affect his whole arm, if kept there, and produce a sort of feeling of lassitude.

When I first made this observation, it was just as novel as puzzling; nobody, wherever I went, would believe it. Meantime I have repeated it with hundreds of sensitives in Vienna; it has been confirmed in England, Scotland, and France; and anyone can easily put it to the proof himself, as sensitives exist everywhere. When they hold their hand near other parts of the crystal, say the bevel-meats on each side, they do, it is true, feel the two sensations of coolness and lukewarmness, but to an incomparably weaker degree than at the two ends, which are opposite poles. Non-sensitives feel nothing at all.

As these contrasting sensations are excited without the crystal being touched, and at a distance of several inches—in fact, in the case of strongly sensitive persons at a distance of several feet—it seemed to be that from these so-to-speak semi-organic stones something was proceeding, emanating, radiating, something as yet unknown to natural science, something which, however incapable we may be of seeing it, still makes its existence known through its effects upon the body. Now sensitives being, so far as feeling is concerned, so very much more capable than other men, the thought occurred to me that they might, in certain respects, be superior to us also in the sense of sight, and perhaps be able, in dense darkness, to perceive something of these peculiar emanations from crystals.

To put this to the proof, one dark night in May 1844 I took an immensely large mountain-crystal with me on a visit to a highly sensitive girl, Miss Angelica Sturmann; her doctor, Professor Lippich, a man celebrated as a pathologist, was present on the occasion. We put two rooms into complete darkness, and in one of them I placed the crystal, in a spot unknown to the others. After pausing a little, to allow our eyes to get accustomed to the dark, we brought the girl into the room where the crystal was. Only a short time elapsed before she told me the place where I had set it down. The whole body of the crystal, she said, was glowing through and through with a fine light, while a body of blue light, the size of one's hand, was streaming out of its peak, in constant motion to and fro, and occasionally emitting sparks; it was tulip-shaped, and disappearing in fine vapour at the summit.

When I turned the crystal round, she saw a dense red and yellow smoke rising over the butt-end. You can imagine how delighted I was with this statement. It was the first observation of thousands of others similar to it, which followed on from that day to this, made with crystals under innumerable variations of conditions, observations which, through the medium of a multitude of sensitive persons, established the fact that the phenomena produced by crystals to the sense of touch are accompanied by phenomena to the sense of vision, the latter phenomena following the former Mari passe, in polar contrast of blue and red-yellow, and only perceptible by sensitives.

If you wish to make these experiments for yourself, I must warn you that you can only expect them to succeed in absolute darkness. The crystalline light is so fine and so extremely weak that if so much as a trace of any other light is perceptible anywhere in the dark chamber, it is sufficient to blind the sensitive observer, that is, to temporarily blunt his excitability of sense for so extremely weak a degree of light. Furthermore, there are but few human beings so highly sensitive to be able, like the young lady I have named, to perceive this delicate light after so short a period of darkness. For sensitives of a middling degree of power it has mostly taken one to two hours in the dark to sufficiently relieve their eyesight from the over-excitation of day- or lamp-light, and thus adequately to prepare it for the detection of the crystal-light. I have even had several cases in which weak sensitives gave no result after three hours, but who nevertheless succeeded quite well during the fourth hour in seeing crystals give out light and in convincing themselves of the reality of the phenomenon.

Now you are impatient to know what this really means, and where these phenomena fit in to physics and physiology, both as to their subjective and objective particulars. They are not heat, although they excite similar sensations to those of lukewarmness and coolness; there is no conceivable source of heat in the case, and, were there any, it would be perceived, not only by sensitives, but also by nonsensitives, or in the ultimate issue by a fine thermoscope. They are not electricity; for there is no excitation present to account for the eternally flowing stream, the electroscope is not affected, and conduction, in accordance with the laws of electricity, is without effect. It cannot be magnetism and diamagnetism, because crystals are not magnetic, and diamagnetism does not take effect in all crystals in the same sense, but in widely differing and contrasted senses—a matter that has no place here at all. It cannot be ordinary light, because, although light is here as an accompaniment, mere light never produces sensations of lukewarmness and coolness, etc. [See Odische Begetenheiten: Poggendorf's objection.]

Well, then, after saying all that, what are the phenomena you have described? If you really wish to know, you compel me to admit that I do not know myself. I am becoming aware through sundry avenues of the presence of a natural force, for which I am unable to find a place on the record established by those forces we already know of. If my judgment of the facts I have been able to gather has not gone astray, this force fits in between electricity, magnetism, and heat, without being identifiable with any of the three; so, in the embarrassment created by the occasion, I have provisionally designated it by the word " Od," the etymology of which I shall discuss later.