jj INTRODUCTION Verses 29-33 relate to the determination of the Sun's longitude from the midday shadow of the gnomon. Verse 34 gives a rule for finding the Sun's declination with the help of the local latitude and the Sun's meridian zemth distance. , t . , . , Verse, 35 relates to the determination of the local latttude with the help of the Sun's declination and the midday shadow of the gnomon. The fourth chapter contains 32 verses and is devoted to the calculation of a lunar eclipse and also to the graphical represen- tation of an eclipse. Verse 1 gives an approximate rule for finding the longitudes of the Sun and the Moon for the time of geocentric opposition or • conjunction of the Sun and Moon. Verse 2 states the mean distances of the Sun and the Moon, and verse 3 gives a rule for finding their true distances. Verse 4 states the measures of the diameters of the Sun, Moon, and the Earth. Verse 5 gives a rule for finding the angular diameters of the Sun and the Moon. Verses 6-7 relate to the determination of the diameter of the Earth's shadow where the Moon crosses it. Verse 8 gives a rule for finding the Moon's latitude for the time of opposition of the Sun and Moon. Verse 9 gives a rule for finding the measure of the Moon's diameter unobscured by the shadow. Verses 10-13 relate to the determination of the durations of eclipse before and after the time of opposition of the Sun and Moon and of the times of the first and last contacts. Verse 14 gives a rule for finding the durations of totality before and after the time of opposition of the Sun and Moon. Verses 15-21 relate to the determination of the so called valana, which is required in the construction of the figure of an eclipse.
