To return to the manifestations:  here are some other cases where Foster identified himself with a personality of his vision. (Bartlett, op. cit., 93.)

    From Sacramento Record, December 8, 1873: 

Foster at one time seized A.’s hand, explaining, “God bless you, my dear boy, my son.  I am thankful I at last may speak to you.  I want you to know I am your father, who loved you in life and loves you still.  I am near to you; a thin veil alone separates us.  Good-by.  I am your father, Abijah A——­”

    “Good heavens!” exclaimed A——­, “that was my father’s name, his
    tone, his manner, his action.”

    “And,” said Foster, “it was a good influence; he was a man of
    large veneration.”

The above indicates what we will provisionally call Possession.  But it is not possession to the extent of complete expulsion of the original consciousness, as in the trances of Home, Moses, and Mrs. Piper.

And which is the following? (Bartlett, op. cit., 103): 

    [Letter to editor, written Nov. 30, 1874]

New York Daily Graphic:  ...  He told me he saw the spirit of an old woman close to me, describing most perfectly my grandmother, and repeating:  “Resodeda, Resodeda is here; she kisses her grandson.”  Arising from his chair, Foster embraced and kissed me in the same peculiar way as my grandmother did when alive.

But here the Possession seems complete (Bartlett, op. cit., 140).  From the Melbourne Daily Age: 

Mr. Foster ... in answer to the question, What he died of? suddenly interrupted, “Stay, this spirit will enter and possess me,” and instantaneously his whole body was seized with quivering convulsions, the eyes were introverted, the face swelled, and the mouth and hands were spasmodically agitated.  Another change, and there sat before me the counterpart of the figure of my departed friend, stricken down with complete paralysis, just as he was on his death-bed.  The transformation was so life-like, if I may use the expression, that I fancied I could detect the very features and physiognomical changes that passed across the visage of my dying friend.  The kind of paralysis was exactly represented, with the palsied hand extended to me to shake, as in the case of the original.  Mr. Foster recovered himself when I touched it, and he said in reply to one of my companions that he had completely lost his own identity during the fit, and felt like waves of water flowing all over his body, from the crown downwards.

Now for some tentative explanation of these rather unusual proceedings.  It is generally known that a hypnotized person will imagine things and do things willed by the hypnotizer, that the sensibility of persons to hypnotism varies, and that persons frequently hypnotized become increasingly susceptible to the influence.