A similar experiment was made with a yet more sensitive subject. This person saw, in the first instance, flames as the first had done; but when the armature of the magnet was applied, the flames did not disappear: she saw flames still: only they were fainter, and their disposition was different. They seemed now to issue from every part of the surface of the magnet equally. It is hardly necessary to add, that these experiments were made in a well-darkened room, and that none of the bystanders could discern what the sensitive subjects saw. Then the following experiment was made:—A powerful lens was so placed as that it should concentrate the light of the flames (if real light they were) upon a point of the wall of the room. The patient at once saw the light upon the wall at the right place; and when the inclination of the lens was shifted, so as to throw the focus in succession on different points, the sensitive observer never failed in pointing out the right spot. To his new force, which Von Reichenbach had now found to emanate likewise from the poles of crystals and the wires of the voltaic pile, he gave the arbitrary but convenient name of Od, or the Od force. His next step was to ascertain the existence of a difference among the sensations produced by Od. Sometimes the current of air was described as warm, sometimes as cool. He found this difference to depend upon the following cause: Whenever the northward pole of a magnet, or one definite pole of a large crystal, or the negative wire of a voltaic battery, is employed in the experiment, the sensation produced is that of a draft of cool air. On the contrary, the southward pole of the magnet, the opposite pole of the crystal, the positive voltaic wire, excite the sensation of a draft of warm air. So the new force appeared to be a polar force, and Von Reichenbach called the first series of the above described manifestations _Od-negative_ effects, the second _Od-positive_ effects. From among his numerous experiments towards establishing the polarity of Od, I select the following:—One of the most sensitive of his subjects held, at his desire, a piece of copper wire, by the middle with the right hand—by one end with the left. Then Von Reichenbach touched the free end of the wire with one pole of a large crystal, in order to charge it with Od. The patient immediately felt a sensation in the right hand, which disappeared as quickly, to be felt by the left hand instead, at the further end of the piece of wire. She then was bidden to take hold of the wire with both her hands at the middle, and then to slide them away from each other to the opposite ends: she observed, on doing so, that sensations were produced which were strong and decided when her hands held the two ends of the wire, and diminished in intensity in proportion as the hands were nearer its middle.