Finally, the third statement which my observations permit me to make, is that the production of forms and luminous phenomena is accompanied with much fatigue on the part of the observers. I have already frequently pointed out this circumstance. On the occasion of the production of the facts described in the present chapter, I noticed certain peculiarities, which I will point out to the attention of experimenters. Fatigue is not felt in an equal degree by all the sitters. Some seem to feel none at all; and, as a rule, these latter are not good auxiliaries. It looks as though some persons were not capable of emitting the force employed. Others, on the contrary, emit it with great facility and tire quickly. I have not been able to study the relation which may exist, between the temperament of these two kinds of sitters and the production of the phenomena; but I have the impression, that this relation ought to exist; it appears to me in a function of the organism rather than in a _rapport_ with the mental condition or moods. This makes one think of the belief professed by spiritists concerning incredulity. In several spiritistic groups failure is attributed to the presence of incredulous sitters; I am persuaded, that the beliefs of experimenters have nothing at all to do with the production of the phenomena observed, though it is certainly necessary to experiment seriously and without bias. I touched upon the results of my observations in that respect, when speaking about the harmony of the circle. The influence of bias would be explained, if the apparent consciousness of the personification could be considered as composed of the elementary consciousness of the sitters. This hypothesis does not appear to me to be demonstrated; but some of my experiments have made me think of its possibility, and I consider it ought to be submitted to examination. Things seem to happen, as though the nervous influx of the sitters created a field of force around the experimenters, and more especially the medium: Each experimenter would then act as a dynamogenic element, and would enter, for a variable part, into the production of the liberated energy. This energy would act beyond the apparent limits of the body, under conditions analogous to those governing its intracorporal action; that is to say, it would remain, to a certain extent, in connection with the superior or inferior nervous centres, conscious or unconscious. In this case we could understand, how the energy appears to depend, to a certain extent, upon the will of the sitters or the medium. We can even explain that it should appear to manifest an independent will, if its production were due to the activity of the nervous centres, the action of which is independent of ordinary consciousness. In that hypothesis, none of the sitters would recognise the trace of their normal personality in the evolution of the phenomena; and this is what generally happens. Sometimes, however, the medium or one of the sitters