(1.) The question of his mental condition at the time of the investigation. It is asserted by Baron Hellenbach (see _Geburt und Tod_ etc., Wien, 1885, S. 96) that Zoellner was of sound mind up to his death. The statement should have due weight, but the author's general attitude towards Spiritism should not be overlooked. I do not consider his testimony for Zoellner's sanity as good as that of Fechner or Scheibner against. Of the four men mentioned as connected with him, Wundt, Weber, Fechner and Scheibner, three (all except Weber) are decidedly of the opinion that his mental condition was not normal. The opinion of Wundt, as of a man whose profession would not permit him to speak hastily upon this topic, I would regard as of special value; but if we rule that out upon the ground that Wundt was not impressed by the investigation, and might naturally be inclined to underrate Zoellner, who was, we have left the opinions of Fechner and Scheibner, both Zoellner's colleagues at Leipsic, both particular friends of Zoellner, and both inclined to agree with him as to the reality of the facts he describes. Both of them regarded Zoellner at the time as of more or less unsound mind. His disease, as described by them, seems to have been chiefly emotional, showing itself in a passionate dislike of contradiction, and a tendency to overlook any evidence contrary to a cherished theory. To the general change in his nature due to his disease Professor Scheibner testifies; and Professor Fechner's belief as to his mental condition is specially worthy of note from the fact that, although recognizing it to be abnormal, he still holds his powers of observation to be sound, and upon this ground is inclined to assent to the facts described. If anyone could be tempted to make Zoellner as sane as possible, it would be one in the position of Professor Fechner. Professor Weber's testimony I will examine later. Upon the question whether the peculiar form of Zoellner's disease would be likely to affect his powers of observation, the following points may throw some light. (2.) It is evident, both from what Zoellner has himself printed and from what Professor Scheibner has said, that Zoellner's interest in the investigation centered in his attempt to prove experimentally what he already held to be speculatively true as to a fourth dimension of space. In a paper published in the _Quarterly Journal of Science_, for April, 1878, he says: