I fancied I saw an advantage, especially for movements without contact, in operating in an uncarpeted room. The carpet not only seems to be a bad element generally, it also hinders the gliding movements of the table, which are often only very slight. As for exterior meteorological conditions, I have noticed that a dry cold favours the production of psychical phenomena: it is, I believe, the temperature _optima_. In any case, the dryness of the air is a very good condition. I have noticed that the phenomena were more easily obtained, when outside conditions favoured the production of numerous sparks under the wheels of electric trams. I have often noticed this coincidence between good sittings and the abundance of electric sparks above-mentioned. I believe that the hygrometrical state of the atmosphere is an important factor in the production of these sparks. Rain and wind are, on the contrary, causes of failure. The lighting of the seance-room is one of the most important considerations in experimentation. Lamps and candles have the inconvenience of taking some time to light, and they do not allow of easy and rapid modification in the illumination of the room. Electric lighting is the best system, because, disposing of several lamps, it suffices to press a hand-lever in order to vary the quantity and quality of the light. Much criticism has been passed on the particular kind of experiments I have undertaken to relate; one of the most frequently reiterated criticisms is the reproach of always operating in obscurity. Nothing can be more inexact. As far as I am concerned, I have never considered as convincing telekinetic and parakinetic experiments made in obscurity. Those movements without contact, which have brought about my conviction, were obtained in full light, and more often in broad daylight. Of course, it is evident that darkness is necessary for the observation of luminous phenomena. To insist upon proving, in broad daylight, the reality of the delicate phosphorescences which it has been given me to observe, is a glaring contradiction. On the other hand, there is no doubt that darkness is particularly favourable to phenomena of a physical order. On several occasions I have had the opportunity of recognising this fact under conditions, which rendered the hypothesis of fraud extremely improbable. For example, I have frequently obtained raps in the light, the number and intensity of which increased when the light was extinguished. It is the same with movements of objects without contact; but, I repeat, obscurity is not necessary. In a popular scientific review I once read a criticism of some experiments in which I took part—a criticism written by a medical man at Bruxelles, if my memory be correct. This doctor, a man of talent, imagined that our conclusions were founded upon experiments conducted solely in total obscurity. He committed an involuntary mistake.