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you on the Horizon, and a line drawn from the eye to that object is a true Meridian line.
Problem 29. To find what two days of the year, the days will be of any given length leſs than ſixteen hours, suppose 10 hours, 20 minutes long?—Rule: Find the Semidiurnal Arc on the index, viz., 5 hours, 10 minutes, both Eaſt and Weſt; lay the director to theſe hours and minutes, on both ſides of the Meridian alternately; then turn the director and the Horizon together, till ſome point in the Ecliptic interſects them both, and the director will then lay over the day of the month required, viz. the 22d of February, and October 19, for anſwer. Again, what two days will be 13 hours, 30 minutes long each? Turn the director to 45 minutes after ſix Weſtward, and move it and the the Horizon together, till ſome point in the Ecliptic exactly interſects them both, and it points out September 1st. for one of the days; and, when brought to 15 minutes past 5, in the morning hours, or Eaſtern ſide of the Meridian, the director points out April 10th. for the other.
Problem 30. To find what two days in the year the Sun will have 50° Meridian Altitude at London? Turn the Meridian of the Index on each ſide of the Tropic of Cancer, till some point of the Ecliptic interſects it in the given Altitude, and in one caſe it points out August 23d. and in the other, April 21st. for answer.
Problem 31. To find the Longitude and Latitude of
