Quick answer:
from the end of book 1
Venus has the same powers and tempered nature as Jupiter, but acts in
the opposite way; for she warms moderately because of her nearness to
the sun, but chiefly humidifies, like the moon, because of the amount
of her own light and because she appropriates the exhalations from the
moist atmosphere surrounding the earth.
Jupiter has a temperate active force because his movement takes place
between the cooling influence of Saturn and the burning power of Mars.
He both heats and humidifies; and because his heating power is the
greater by reason of the underlying spheres, he produces fertilizing
winds.
Mercury in general is found at certain times alike to be drying and
absorptive of moisture, because he never is far removed in longitude
from the heat of the sun; and again humidifying, because he is next
above the sphere of the moon, which is closest to the earth; and to
change quickly from one to the other, inspired as it were by the speed
of his motion in the neighbourhood of the sun itself.
Long answer:
The vision of Ptolemy was modelled after Aristoteles in which the eart was at the center and the different cosmic object were positioned around on different spherical object, with the "fixed stars" at the end.
Ptolemy differentiates between two types of astronomical study: the first (astronomy proper) which discovers the astronomical cycles and movements; the second (astrology) which investigates the changes these movements bring about. The Tetrabiblos describe the latter.
The biggest influence was from (other than sun and moon) from planets in pairs::
- Beneficent and Maleficent
- Masculine and Feminine
- Diurnal and Nocturnal
Fixed stars where then classified based on the planets:
As it is next in order to recount the natures of the fixed stars with
reference to their special powers, we shall set forth their observed
characters in an exposition like that of the natures of the planets,
and in the first place those of the ones that occupy the figures in
the zodiac itself.
Was it considered useful?
Ptolemy uses 2 chapters (chapter 2 and chapter 3 of book 1) to discuss 2 arguments against astrology:
- the complexity of the subject makes its claim of providing reliable foreknowledge unattainable
- reliable foreknowledge—if it can be attained—would imply such fatalism as to make the subject's purpose useless (since if the future is predictable, anything which is destined to happen will happen whether predicted or not)
The conclusion (from Ptolemy) is:
it would not be fitting to dismiss all prognostication of this
character because it can sometimes be mistaken, for we do not
discredit the art of the pilot for its many errors;[...]
and
just as with prognostication, even if it be not entirely infallible,
at least its possibilities have appeared worthy of the highest regard,
so too in the case of a defensive practice, even though it does not
furnish a remedy for everything, its authority in some instances at
least, however few or unimportant, should be welcomed and prized and
regarded as profitable in no ordinary sense.
Is Tetrabyblos orginal content?
While wikipedia states
Much of the content of the Tetrabiblos was collected from earlier
sources; Ptolemy's achievement was to order his material in a
systematic way, showing how the subject could, in his view, be
rationalized. It is, indeed, presented as the second part of the study
of astronomy of which the Almagest was the first, concerned with the
influences of the celestial bodies in the sublunary sphere.
It is hard to find the specific references (no bibliography were included at the time, and we don't even know the exact original name of "Tetrabiblos").
A source states that
...Why did Ptolemy pay so much attention to the seemingly marginal
doctrine of the Terms? ... The classical version of this system was
attributed to “the Egyptians,” that is: to Nechepso the King and
Petosiris his High Priest. Under these pseudonyms, which evoke the
idea of a far remote age, the core of Hellenistic astrology had in
truth been created and dispersed by unknown, Greek writing authors
in the second or first century BCE
(emphasis is mine)
We may conclude that we know that the content is not original because it has been found similar content on previous sources
