At The Parliament of Religions in Chicago 1893, Swami Vivekananda spoke about Paper on Hinduism. A part of it contains this:
There is another suggestion. Taking all these for granted, how is it that I do not remember anything of my past life ? This can be easily explained. I am now speaking English. It is not my mother tongue, in fact no words of my mother tongue are now present in my consciousness; but let me try to bring them up, and they rush in. That shows that consciousness is only the surface of the mental ocean, and within its depths are stored up all our experiences. Try and struggle, they would come up and you would be conscious even of your past life.
This is direct and demonstrative evidence. Verification is the perfect proof of a theory, and here is the challenge thrown to the world by the Rishis. We have discovered the secret by which the very depths of the ocean of memory can be stirred up — try it and you would get a complete reminiscence of your past life.
What is this secret of revealing our past lives that Swamiji was talking about?