The Astronomical Observatories of Jai Singh c20.s1.16

c20.s1.16

**Houses.**—The astrological houses (*Domus cœli*) must not be confused with the planetary domiciles. The system of twelve houses was not altogether accepted by Ptolemy, but since the date of Sextus Empiricus (3rd century of the present era) it has been in universal use.⁴ In plate V and figure 17 the twelve houses are shown. The boundary lines pass through the intersection (*H*) of the horizon and meridian, and cut the equator at equal intervals of thirty degrees. The points at which these boundary lines cut the ecliptic are termed the cusps (*Cuspides domorum*), and four of these are at once seen (*E*, *t*, *W* and *A* in plate V), but to find the others is a mathematical problem of some little difficulty, and occupied the attention of al-Battānī, Regiomontanus, Jean-Antoine Magini (1556-1617) and others. According to Delambre (p. 501), the Arabs divide the south-east quadrant of the equator (*S.E.* in plate V) into spaces each equivalent to two temporal day hours, and the next quadrant (*E.N.*) into corresponding spaces of night hours.⁵ Campanus and Gazulus divide the prime vertical (*EZW*), instead of the equator, into equal divisions, and so on.