Required the correfponding hour with the following latitudes, fun's altitude, and days of the month.

Bethlehem, lat. 32, Jan. 6, fun's altitude 20°. -Babylon, lat. 34, April 21, fun's altitude 30°. -Dover, lat. 51, Jan. 7, fun's altitude oo.Paris, lat. 49, Jan. 21, fun's altitude 6o-Ferns, lat. 52, Nov. 29, fun's altitude 10°.-Hackney, lat. 51, April 10, fun's altitude 15°.-York Town, lat. 37, Oct. 19, fun's altitude 13o.Annonay, lat. 45, Nov. 21, fun's altitude 7°.

PROBLEM XVII.

To find the Time of the Sun's rifing and fetting, and confequently the Length of any particular Day and Night, in a given Latitude, or at any propofed Place.

Rectify the globe for the given latitude, or place, and day of the month, agreeably to the directions given in the 12th problem; then revolve the globe till the fun's place comes in contact with the Eaftern verge of the horizon; and if the hour circle have a double row of figures*, the index will at once fhew the time of the fun's rifing, and the period of its fetting the number of intervening hours is the length of the day required, which fubtracted from 24 will give the duration of the night. But if the hour circle have no more than a fingle row of figures, the operation juft mentioned will only point out the time of the fun's

:

Similar to thofe, for inftance, on the globes made by Mr. Bardin. See p. 4.

rifing;

rifing; and its fetting must be found in like manner, by bringing the fun's place to the Weftern edge of the horizon.

N. B. The hour of fun-fetting doubled gives the length of the day, and the hour of fun-rifing doubled gives the length of the night.

Another method of performing this problem: Rectify the globe for the affigned latitude; find the fun's place for the given day, and bring it to the Eastern verge of the horizon; fet the index to 12 at noon; turn the globe till the fun's place touch the Western verge of the horizon, and obferve by the index the number of hours which have intervened during the operation; and thefe will be the length of the day required. If the length of the propofed day do not exceed twelve hours, the hour to which the index points when the fun's place is brought to the Western edge of the horizon is its length but if it do exceed 12 hours, the time to which the index then points must be added to 12, and the total of thefe will give the answer fought.

EXAMPLES.

What is the length of the day at London, lat. 511, at the fummer and winter folftices ?—Anf. 16 hours at the former period; 7 hours at the latter.

Required the length of the following days at the places mentioned. Oct. 12, at Guanahani, or St. Salvador, lat. 24 North.-March 15, at Palos, lat. 37.-May 20, at Valladolid, lat. 41.-Oct. 16, at Arnheim, lat. 52.-May 19, at London, lat. 51.-Oct. 25, at St. Quintin, lat. 484May 3, at Paris, lat. 49.-Aug. 2, at Blenheim, lat. 481.-July 22, at Gibraltar, lat. 36.

N. B.

N. B. This problem may also be solved by the fcale of declination, in the following manner :

Having rectified the globe for the affigned latitude, bring the middle part of the scale to the meridian, and fet the index to 12; then bring the given day in the scale to the Eastern fide of the horizon; and the index will fhew the time of the fun's rifing and fetting; if the hour circle have a double row of figures; if it have only a fingle row, the fetting muft be fought by turning the fcale to the Western fide of the horizon.

PROBLEM XVIII.

To find the Length of the Longest Day and shortest Night in any given Place, or affigned Latitude, not exceeding 66 Degrees in the Northern Hemifphere.

Rectify the globe for the given latitude, or propofed place; bring the fummer folftice, or firft degree of Cancer (which is the utmost recefs of the fun from the equator Northwards, and confequently the boundary of the length of days in the Northern hemifphere) to the meridian; fet the index to 12 at noon, and revolve the globe till the fun's place, i. e. the beginning of Cancer, come in contact with the Eastern verge of the horizon, and the index, on a globe with a double hour circle, will point to the time of the fun's rifing and fetting the intervening hours are the length of the longeft day in the latitude propofed. If the globe have only a fingle hour circle, the above operation will give the time of the fun's rifing; and its time of fetting must be fought by bringing the fun's place to the Western edge of the horizon.

E

Another

Another method of folving this problem: Rectify the globe for the latitude mentioned; bring the first degree of Cancer to the Eastern fide of the horizon; place the index to twelve at noon; then revolve the globe till the fame degree of the ecliptic touches the Western edge of the horizon; and, finally, count the number of hours which the index has paffed over during the revolution of the sphere.

N. B. The length of the longest day deducted from 24 will give the duration of the shorteft night; and allowing one for every half hour which the longest day contains above 12 hours, will give the climate in which the propofed place is fituated. A part of half an hour must be accounted another climate; e. g. where the longest day is 12 hours the place is in the fecond climate.

EXAMPLES.

What are the longest day and the shortest night at London, and in what climate is it fituated? -Anf. 16 hours the longest day, 7 hours the shortest night; and London is fituated in the oth climate.

Required the length of the longeft day, the fhortest night, and the climate in which the following places are fituated: Tobago, St. Salvador, Bombay, Pekin, Toulon, Mofcow, Bergen, Archangel, Cherfon, Marseilles, Rhodes, Meffina, Zante, Jerufalem, Calcutta, Mecca, Medina, Smyrna, and Goa.

* See Art. 16. p. 19.

PROBLEM

PROBLEM XIX.

To find the Length of the longest Day and the shorteft Night in any given Place, or affigned Latitude, not exceeding 66 Degrees in the Southern Hemisphere.

This problem is folved exactly in the fame manner as the preceding one, only the South pole must be elevated inftead of the North, and the first degree of Capricorn fubftituted for the first degree of Cancer; because that point of the ecliptic fhews the fun's greatest recefs from the equator Southward, and, of courfe, exhibits the boundary of the longest day in the Southern hemifphere.

N. B. This problem cannot be worked with globes which have the hour-circle attached to the exterior furface of the brafs meridian, because that circumstance prevents the South-pole from being elevated; and globes of this defcription are moreover deficient in a Southern hour-circle.

EXAMPLES.

What is the length of the longest day and the fhortest night, and in what climate is a place which is fituated in 51 deg. of South latitude ?-Anf. Longeft day 16 hours; shortest night 7 hours; climate the 9th.

Required the length of the longest day, the fhortest night, and the climate, of the following places: Juan Fernandez, Cape of Good Hope, Cape Horn, Buenos Ayres, Baldivia, Rio Janeiro, Lima, Potofi, Arica, Truxillo, St. Salvador, Quito,.

E 2

Otaheite,