Seeing one’s own double

(…)
Comparing a large number of cases Dr. Sollier found that the apparition has many degrees from the simple impression of being in one’s own presence to the clear vision as if in a mirror. In the last case the apparition is sudden and does not last long. Any excitement whatever will make it disappear. When the phantom has different attributes, is smaller in stature, different in clothes, it may persist for hours in different intensity. The moment of apparition is usually during the evening hours, in states of deep meditation, self-concentration or anaesthesia. The distance at which it is seen varies from a few yards to close proximity. Sometimes it marches before the subject and vanishes all at once, sometimes it turns about or moves to the side and imitates his movements. In most cases it is silent. Occasionally there is a dialogue and difference of opinion between phantom and self. When the phantom has different attributes his clothes are usually black and the ressemblance is like that of a brother. The costume, however, may be identical with that of a favourite romantic hero or with one worn in the past.

From: Encyclopedia of Psychic Science by Nandor Fodor, University Books, 1966, excerpt from entry: “seeing one’s own double”