Se< 5 t» 3 » Globes.

m Pr ob. XXIV. To find the Time when totalDarkness ceases , or when the Twilight con-tinues from Sun-Jetting to Sun-* risings inany given Place.

. Let the Place be in the Northern Hemi-sphere; then if the Complement of theLatitude be greater than (the Depression)18 Degrees, subtract 18 Degrees from it,and the Remainder will be the Sun’s Decli-nation North, when total Darkness ceases.But if the Complement of the Latitude is letsthan 18 Degrees, the Difference will bethe Sun’s Declination South, when the Twi-light begins to continue all Night. If theLatitude is South, the only Difference willbe, that the Sun’s Declination will be onthe contrary Side.

Thus at London > when the Sun’s Decli-nation North is greater than 2 oi Degrees,there is no total Darkness, but constantTwilight, which happens from the 15th ofMay to the 7th of July, being near twoMonths. Under the North Pole the Twi-light ceases, when the Sun’s Declination isgreater than 18 Degrees South; which.isfrom the ad of November , till the 18th ofJanuary: So that notwithstanding the Sunis absent in this Part of the World for halfa Year together, yet total Darkness does notcontinue above 11 Weeks $ and besides, the

Moon

14 $