What follows is my provisional translation (in other words, not official or authorized; see here for more) of a passage from a Tablet of ‘Abdu’l-Bahá, the original text of which has been published in Yárán-i-Pársí, p. 340 (selection no. 454).
As to the matter of the conjuring of spirits which is now mentioned among the people, this is mere superstition, and certain displays are brought about by contrivances. Were it true, there would be no need for earthly measures and economic techniques. Any ruling authority would choose a person to communicate with spirits and consult them on the realities of events. But when the human soul acquireth strength, refinement, and sanctification, it becometh a medium for the truths of things, revealing their secrets. The same applieth to one’s rational faculty. What thou seest in the realm of visibility was once hidden; the human soul hath unveiled it and brought it out of the invisible plane into the visible world.
A typescript of the original Persian text of the passage appears below (all punctuation mine).