The reason why the beings directing a _seance_ find it easier to operate in darkness or in very subdued light will now be manifest, since their power would usually be insufficient to hold together a materialized form or even a "spirit hand" for more than a very few seconds amidst the intense vibrations set up by brilliant light. The _habitues_ of _seances_ will no doubt have noticed that materializations are of three kinds:--First, those which are tangible but not visible; second, those which are visible but not tangible; and third, those which are both visible and tangible. To the first kind, which is much the most common, belong the invisible spirit hands which so frequently stroke the faces of the sitters or carry small objects about the room, and the vocal organs from which the "direct voice" proceeds. In this case, an order of matter is being used which can neither reflect nor obstruct light, but which is capable under certain conditions of setting up vibrations in the atmosphere which affect us as sound. A variation of this class is that kind of partial materialization which, though incapable of reflecting any light that we can see, is yet able to affect some of the ultra-violet rays, and can therefore make a more or less definite impression upon the camera, and so provide us with what are known as "spirit photographs". When there is not sufficient power available to produce a perfect materialization we sometimes get the vaporous-looking form which constitutes our second class, and in such a case the "spirits" usually warn their sitters that the forms which appear must not be touched. In the rarer case of a full materialization there is sufficient power to hold together, at least for a few moments, a form which can be both seen and touched. When an Adept or pupil finds it necessary for any purpose to materialize his Mayavirupa or his astral body, he does not draw upon either his own etheric double or any one else's, since he has been taught how to extract the matter which he requires directly from the astral light or even from the Akasha. [Sidenote: Reduplication.] Another phenomenon closely connected with this part of the subject is that of reduplication, which is produced by simply forming in the astral light a perfect mental image of the object to be copied, and then gathering about that mould the necessary physical matter. Of course for this purpose it is necessary that every particle, interior as well as exterior, of the object to be duplicated should be held accurately in view simultaneously, and consequently the phenomenon is one which requires considerable power of concentration to perform. Persons unable to reduce the matter required directly from the astral light have sometimes borrowed it from the material of the original article, which in this case would be correspondingly reduced in weight. [Sidenote: Precipitation.]