The rectification by the trutine of Hermes in Lilly merchant’s chart

Of the three books of Christian Astrology the most famous is obviously the second dedicated to horary which eclipses the rest of the work, especially the third, about nativities, which is a pity because the third contains some important chapters, like the one about temperament or the one about the rectification of the birth hour, which we are going to recalculate in this post. This is Lilly’s “English merchant”


With a modern  software:


 The Trutine of Hermes is a rectification’s method of the birth time based on the Moon, which is a natural significator of women and pregnancy.

The first evidence of this rule is preserved by Antiochus and attributed to Petosiris, and from him mentioned by many Hellenistic authors. The pseudo-Centiloquium so states:

51. In what sign the Moon is at the time of birth, make that sign the ascendant in conception; and in what sign she is found at the conception, make that or its opposite the sign ascending at the birth.

The lenght of pregnancy since Babylonian times was established in 273 days, which are ten sideral months.

In fact the Moon takes 1 month to accomplish a whole revolution of the zodiac. In ten months

10 x 360°= 3600 °

The mean diurnal motion of the Moon is 13°10’35”

so for the Moon it takes 273 days

3600 :  13°10’35” =

3600 : 13, 17638 = 273 days

1- Let us see where the Moon is in the chart we want to rectify.

If the Moon is below the horizon one should count the distance between the Ascendant and the Moon and consider 1 day each 12 degrees, and add to 273.

If the Moon is above the horizon one should count the distance between the Ascendant and the Moon and consider 1 day each 12 degrees, and take away from 273 (or the distance between the Descendant and the Moon and add to 258, which is the same).

We will call this number x.

2- We shall take away x days from the birthday, and we get the conception day.

3 – we will see where the Moon is. This will be the ascendant or the descendant of the birth chart.

We can use this method in order to recalculate our birth time.

Let us how Lilly rectifies the Merchant’s chart.

The Moon is below the horizon, in the 5th house at 1 Gemini, the Ascendant is 6 Capricorn: they are distant 145 degrees, 4 signs and 25 degrees.
So we shall add to 273  12 days (145/12)

So 273+12= 285 days pregnancy lenght.

Lilly gives the following table, which is the same.


The merchant was born on September, 19 1616 ( a leap year) which is 264-th day of the year.

Since the pregnancy lasted 285 days, the Merchant was conceived on December, 10

In fact 285-264= 21

December 1615  has 31 days

31-21= December 10th, which is the conception day.

Then we make the Moon degree at the birth – 1.40 Gemini– the Ascendant of conception and we see where the Conception Moon falls, at 0.20 Capricorn


So 0.20 Capricorn will be the rectified Ascendant. This is the rectified chart.


Enjoy 🙂

2 thoughts on “The rectification by the trutine of Hermes in Lilly merchant’s chart

  1. Merci, j’ai fait le calcul (née à 9h40 le 11 décembre 1954 à Renaix à 26 km de Tournai, naissance de CLOVIS. (Basilique Saint Hermès). Ascendant: 11 degré du taureau. en plus il y a beaucoup de sychronicités avec votre exemple. Ascendant à 0, 20 degré du capricorne. Le degré d’arche correspond bien, mais je ne suis pas du tout envieuse…

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