THIRD DISCOURSE.

Abú Rayḥán Bírúní says in the first chapter of his
“Explanation of the Science of Astrology” (*Kitábu't-Tafhím
fí ṣaná'ati 't-tanjím**):

“A man does not deserve the title
of Astrologer until he attains proficiency in four sciences:
*first*, Mathematics; *secondly*, Arithmetic; *thirdly*, Cosmography;
and *fourthly*, Judicial Astrology.”

Now *Mathematical Science* is that whereby are known
the natures and qualities of lines and geometrical figures,
plain and solid, and the general relations of quantities,
and what partakes of the quantitative nature, to what has
position and form. It includes the principles of the Book
of Euclid the geometrician*

in the recension of Thábit ibn Qurra.*

*Arithmetic* is that science whereby are known the natures
of all sorts of numbers;*

the nature of their relation to
one another; their generation from each other; and the
applications thereof, such as halving, doubling, multiplication,
division, addition, subtraction, and Algebra. The principles
thereof are contained in the book of the *Takmila*) of Abú Manṣúr
of Baghdad,*

and the “Hundred Chapters” (*Ṣad Báb*) of
as-Sajzí.*

*Cosmography* is that science whereby are known the natures
of the Celestial and Terrestrial Bodies,*

their shapes and positions, their relations to one another, and the measurements and distances which are between them, together with the nature of the movements of each one of the stars and heavens, and the co-ordination of the spheres, axes, and circles whereby these movements are fulfilled. It includes a knowledge of the Al-Magest and the best of its commentaries and elucidations, which are the Commentary of Tabrízí*

and the Al-Magest of Shifá. And amongst the applications of this science is the science of the Calendar and of Almanacs.

*Judicial Astrology* is a branch of Natural Science, and
its special use is prognostication, by which is meant the
deducing by analogy from configurations, and from an
estimation of the degrees and zodiacal signs and their
influences, those events which are brought about by their
movements, in respect to the condition of the cycles of
the world, politics, cities, nativities, changes, transitions,
decisions, and other questions; and it is contained in these
five [books] which we have enumerated, to wit, the writings
of Abú Ma'shar of Balkh,*

Aḥmad 'Abdu'l-Jalíl-i-Sajzí, Abú Rayḥán Bírúní, and Gúshyár-i-Jílí.*

So the Astrologer must be a man of acute mind, approved
character, and great natural intelligence. And one of the
essentials of this art is that the astrologer who would
pronounce prognostications should possess in his own
horoscope the Share of the Unseen, and that the Lord of
the House of this Share of the Unseen should be lucky,
and in a favourable position, in order that such pronouncements
as he gives may be near the truth. And one of the
conditions of being a good astrologer is that he should have
in mind the whole of the “Principia” (*Uṣúl*) of Gúshyár,
and should continually study the “Opus Majus,”*

and
should look frequently into the *Qánún-i-Mas'údí**

and the
*Jámi'-i-Sháhí*, so that his knowledge and concepts may be
refreshed.