Marc Edmund Jones had, by the early 1920s, established himself as a serious writer on astrology within the Theosophical circles of Southern California. He conceived an experiment: to obtain, through a clairvoyant working blind and unprompted, a symbolic image for every one of the 360 degrees of the zodiac, in a single unbroken session. In 1923 he met Elsie Wheeler, a clairvoyant medium confined to a wheelchair by severe arthritis, whose gift he had come to admire, and he asked her to be his partner in the undertaking.
On an unrecorded day in 1925, the two of them carried out the experiment on a park bench in Balboa Park, San Diego. Jones read out each degree of the zodiac in turn, in an order chosen to prevent Wheeler from anticipating a pattern, and Wheeler spoke a brief visualized image for each one as it came to her, with no time to deliberate and no chance to revise. The whole set of 360 images was produced verbally, in Jones's presence, over the course of that single day, becoming the raw material of what is now called the Sabian Symbols. Jones did not read the degrees to her in zodiacal order; he called them out in a scrambled sequence specifically so Wheeler could not track her position in the circle and unconsciously shape her images to an expected progression from one sign to the next. The images she returned, delivered without pause or revision, ranged from the domestic to the strange, an ordinary schoolroom beside a witch riding a broomstick, and Jones kept the full transcript rather than editing it down before beginning the long work of interpreting it.