Then you remember that Von Reichenbach has shown, that the two ends of a large crystal, moved along and near the surface of a limb, in certain sensitive subjects, produced decided but different sensations, one that of a draught of cool air, the other of a draught of warm air. That the proximity of the northward pole of a magnet again produces the former, of the southward pole the latter; of the negative wire of a voltaic pile, the former, of the positive wire, the latter; finally, that _the two hands_ are equally and similarly efficient, the right acting like the negative influence, the left like the positive, of those above specified. Von Reichenbach came to the conclusion, from these and other experiments, that the two lateral halves of the human body have opposite relations to the influence, the existence of which he has proved, while he has in part developed its laws. And he throws out the very idea of a transverse polarity reigning in the animal frame. Do you remember, in confirmation of it, one of the most curious experiments which he leads Fraeulein Maix to execute; valueless it might be thought if it stood alone, but joined with parallel effects produced on others, its weight is irresistible. Miss M. holds a bar magnet by its two ends. In any case it is sensibly inconvenient to her to do so. But when she holds the southward or positive pole of the magnet in her right hand, the northward or negative pole in her left, the thing is bearable. When, on the contrary, she reverses the position of the magnet, she immediately experiences the most distressing uneasiness, and the feeling as of an inward struggle in her arms, chest, and head. This ceases instantly on letting go the magnet. I will not inflict upon you more of Von Reichenbach, though sorely tempted, so much is there in common between his Od and the influence investigated by the Count de Tristan. If you know the researches of the former already, why _verbum sat_; if not, I had better not attempt further to explain to you the _ignotum per ignotum_.