Necromancy: The raising of the images of the dead; black magic.  Moses,  condemned the "witches" of his day to death, the said witches being often only mediums, e. g., the case of the witch of Endor and Samuel.--H. P. Blavatsky

Mediumship: That abnormal psycho-physiological state which leads a person to take the fancies of his imagination, his hallucinations, real or artificial, for realities.  No entirely healthy person on the physiological and psychological planes can ever be a medium. --H. P. Blavatsky

Black Magic: Sorcery; necromancy, or the raising of the dead and other selfish abuses of abnormal powers.  This abuse may be unintentional; still it has to remain "black" magic whenever anything is produced phenomenally simply for one's own gratification or amusement. --H. P. Blavatsky

Anyone . . . who attempts to cultivate . . . hypnotism, mesmerism, or even the secrets of producing physical phenomena, etc., without the knowledge of the philosophic rationale of those powers, is like a rudderless boat launched on a stormy ocean . . .

. . . the eidolon of the ex-personality is left alone in its new abode.  Here, the pale copy of the man that was, vegetates for a period of time . . . . Bereft as it is of its higher mind, spirit and physical senses, . . it will gradually fade out and disintegrate.  But if forcibly drawn back into the terrestrial sphere, whether by the passionate desires and appeals of the surviving friends or by regular necromantic practices --one of the most pernicious of which is mediumship-- the "spook" may prevail . . . . Once the Kama Rupa (eidolon) has learned the way back to living human bodies, it becomes a vampire feeding on the vitality of those who are so anxious for its company.  In India,
these Eidolons are called Pisachas, and are much dreaded.

Materializations . . . are produced by the larvae, the eidolons, or Kama Lokic "ghosts" of dead personalities . . . . They are present around us, but being on another plane do not see us any more than we see them.  But whenever the . . . desires of living men and the conditions furnished by the abnormal constitutions of mediums are combined together, these eidolons are . . . pulled down from their plane on to ours and made objective.  This is necromancy; it does no good to the dead, and great harm to the living, in addition to the fact that it interferes with a law of nature  . . .

Hallucinations . . . when produced through mediumship, are preceded by a relaxation of the nervous system, generating invariably an abnormal magnetic condition which attracts to the sufferer waves of astral light . . .

. . . others see in mesmerism the great secret of ancient magic.  One and all of those who put their theory into practice are rapidly drifting, through ignorance, into black magic.

. . . . Gnomes, Sylphs and Undines, as the service agents of the occultist, may produce various effects; but if employed by . . . Kama Rupas . . . they enslave the mediums . . .

The Conscious Individuality of the disembodied cannot materialize, nor can it return from its own Devachanic sphere to the plane of terrestrial objectivity.

In truth there is neither ascending nor descending, but a change of state or condition for the medium.  The body of the latter becoming paralyzed or "entranced, the spiritual Ego is free from its trammels, and finds itself on the same plane of consciousness with the disembodied spirits.  Hence, if there is any spiritual attraction between the two they can communicate, as often occurs in dreams . . . . the liberated spirit of a medium has the opportunity and facility of influencing the passive organs of its entranced physical body, to make them act, speak, and write at its will.  The Ego [without the influence of Mind] can make it repeat echo-like, and in the human language, the thoughts and ideas of the disembodied entity [Seth Speaks], as well as its own . . .

Hypnotic power has been discovered almost by accident, the way to it having been prepared by mesmerism; and now an able hypnotist can do almost anything with it, from forcing a man, unconsciously to himself, to play the fool, to making him commit a crime --often by proxy for the hypnotist, and for the benefit of the latter . . .

Stevenson has used hypnotism in a few cases, but admits "I haven't succeeded in a single case" in obtaining through his experiments verifiable information on what seemed to be a previous life.  "I think most domestic experiments in this area are worthless.  People don't understand what they're getting into, and they're usually just tapping their own subconscious minds.  Then they come up with fiction and novels.  Occasionally, they may get into trouble.  There have been cases of people becoming so absorbed with these alleged spirits that they haven't been able to get rid of them.  They've become sort of preoccupied.  There have been . . . cases of people becoming psychotic."

. . . Do you not see the tremendous evils that lie concealed in hypnotism? . . . Hypnotism and suggestion are great and dangerous powers, for the very reason that the victim never knows when he is being subjected to them; his will is stolen from him . . . . Whoever lets himself or herself be hypnotized, by anyone, good or bad, is opening a door which he will be powerless to shut; and he can not tell who will be the next to enter!  If you could foresee what I foresee, you would begin heart and soul to spread the teaching of universal brotherhood.  It is the only safeguard!

. . . the scientist is wandering in the dark, confounded and confused by all that hypnotism and other strange things bring before him, because the conscious Man is out of sight on the very top of the divine mountain . . .

Hypnotism is trespass into the territory of another's consciousness . . . a negative psychological effect ensues that in time deranges the brain cells.