A man named Marc Edmund Jones worked with a psychic named Elsie Wheeler, and she used her powers to describe what she clairvoyantly "saw" in each of the 360 degrees of astrology. This was in the mid 1920's, when many were involved in the scientific reorganization of Astrology itself. Jones decided to publish the Sabian Symbols in 1932, but Dane Rudhyar became interested. He brought more attention to them in The Astrology of the Personality, reprinted as a mass-market paperback in New York in 1969. The Wheel of Significance is the 3rd volume found in the books called The Lost Writings. The first was The Universal Matrix, a work on the Zodiac and it's energies, and the 2nd was about the 12 houses of Astrology, The Way of Creative Accomplishment.
The Sabian Symbols came to my attention in an Astrology workshop I took in the mid 1970's. They are very accurate, and give a description for each of the 30 degrees of all 12 Zodiac signs. Their accuracy gives me chills! I found copies of my Sabian Symbols when looking for an old horoscope a few months ago, and was astonished to see The Wheel of Significance, in Kindle version no less, right on Amazon! If you are an Astrologer you will enjoy looking up the definitions of each degree in a person's chart. I was not aware Dane Rudhyar's work was "lost" as I found it quite easily, though it was not cataloged here.