22
tract the Oblique Aſcenſion from it, and it leaves 12° 40', which is the Aſcenſional Difference required.—Obſerve the ſame rule with the Moon, Planet, or any Star.
Problem 8. To find the time of Sun-riſing, and length of the day and night, on February 4th and Auguſt 9th. Bring the Sun's place to the Horizon, Eaſtward, and lay the director through it into the Hour Circle, and it points to 25 minutes paſt 7. For riſing on February 4th, ſubtract this from 12 hours, and the remainder is the Sun's Semi-diurnal Arc, 4 hours, 35 minutes, which doubled, is 9 hours, 10 minutes, for the length of the day; but ſubtract this 9 hours, 10 minutes, from 24 hours, and the remainder is the Nocturnal Arc, or the length of the night, 14 hours, 50 minutes, as required; but, on Auguſt 9th, the Sun riſes 25 minutes before 5; therefore, the Semi-diurnal Arc is 7 hours, 25 minutes, which doubled, makes 14 hours, 50 minutes, for the length of the day, which, ſubtracted from 24 hours, leaves 9 hours, 10. minutes, for the length of the night required.
Problem 9. To find the length of the longest and ſhorteſt days at London. Bring the firſt point of Cancer to the eaſtern Horizon, lay the director, through it, and it points to 3 hours, 47 minutes, A. M. or 13 minutes before 4 in the morning, ſubtract this from 12 hours, and it leaves 8 hours, 13 minutes for the Semi-diurnal Arc, which doubled, gives 16 hours, 26 minutes for the length of the day; but, ſubtract this
