This section is from the book "Astrology", by M. M. Macgregor. Also available from Amazon: Astrology.
Besides the Elemental Triunes, or rather Triunes of Elements, into which the twelve signs of the Zodiac are divided—where each element is divided from its two companions by three other elements in between—there is another set of Trinities. These are not divided from each other, three successive months forming a Trinity. And studying the signs in threes in this way there will be found in spite of the difference in the elements an underlying likeness. This is sometimes so strong that people of adjoining signs will often become very good friends with many sympathies in common. But this sympathy should not be mistaken for love, as sometimes happens, in the case of adjoining fire and water, for there would not be likelihood of much peace in such a union. These four successive Trinities occupy the Spring, Summer, Autumn and "Winter, seeming to obtain their character from the season of the year.
The first is the Intellectual Trinity. It begins March 21st and ends June 21st, taking in Aries, Taurus and Gemini. The second is the Maternal Trinity. It begins June 21st and ends September 22d, taking in Cancer, Leo and Yirgo. The third is the Reproductive Trinity. It begins September 22d and ends December 21st, taking in Libra, Scorpio and Sagittarius. The fourth is the Serving Trinity. It begins December 21st and ends March 21st, taking in Caprioornus, Aquarius and Pisces.
Both the Head Signs of the Elemental Triunes, and the Head or first Signs of these latter Trinities partake most strongly of the element or general principles of the Trinities. They are apt to be independent, self-reliant, assertive and even too self-sufficient at times, inclined to deal in generalities and neglect detail. The second or Middle Signs in both Trinities deal with the more interior thoughts and qualities of the Sign and are not so apt to be public characters. The third or Last Sign answers to the first. It is the Executive. It carries out the plans and makes possible and practicable the ideas of the Head.
 
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