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22 the Oblique Acenion from it, and it leaves 12° 40', which is the Acenional Difference required.—Oberve the ame rule with the Moon, Planet, or any Star.

Problem 8. To find the time of Sun-riing, and length of the day and night, on February 4th and Augut 9th. Bring the Sun's place to the Horizon, Eatward, and lay the director through it into the Hour Circle, and it points to 25 minutes pat 7. For riing on February 4th, ubtract 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 ubtract 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 Augut 9th, the Sun ries 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, ubtracted 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 hortet days at London. Bring the firt point of Cancer to the eatern Horizon, lay the director, through it, and it points to 3 hours, 47 minutes, A. M. or 13 minutes before 4 in the morning, ubtract 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, ubtract this