PROBLEM XVI. : The day and hour at any place being given to find where the sun is rising, where he is setting, where it is noon, where it is midnight where it is twilight in the morning, and where it is twilight in the evening. RULE.-Find, by problem 9th, the place to which the sun is then vertical; rectify the globe for the latitude of that place, and bring it to the brass meridian. All the places along the western edge of the horizon have the sun rising; those places along the eastern edge have the sun setting; those under the brass meridian above the horizon have noon; those under the brass meridian below the horizon, have midnight; those places that are less than 18° below the western edge of the horizon have twilight in the morning; and those that are less than 18° below the eastern edge, have twilight in the evening. Find where the sun is rising, where he is setting, where it is noon, where it is midnight, where it is twilight in the morning, and where it is twilight in the evening, at the following places 1. Newcastle, November 11th, at 10 o'clock, A. M. The day and hour being given when an eclipse of the sun will happen, to find where it will be visible. RULE. Find by problem 9, the place to which the sun is vertical at the given time; rectify the globe for the latitude of that place, and bring it to the brass meridian. To all the places within 70° of this place, the eclipse, if a considerable one, may be visible. 1. On the 29th of November, 1826, at four minutes past eleven o'clock in the morning, at London, there was an eclipse of the sun, where was it visible? 2. On the 15th of May, 1836, at half-past two o'clock in the - 1.. 系 afternoon, at London, there will be an eclipse of the sun, where will it be visible? PROBLEM XVIII. The day and hour being given, when an eclipse of the moon will happen, to find where it will be visible. RULE.-Find by problem 9, the place to which the sun is vertical at the given time, rectify the globe for the Antipodes of that place, and bring the Antipodes to the brass meridian. To all the places above the horizon the eclipse will be visible. 1. On the 13th of September, 1829, at half-past six o'clock in the morning, at London, there will be an eclipse of the moon where will it be visible? 2. On the 9th of March, 1830, at two o'clock in the afternoon, at London, there will be an eclipse of the moon, where will it be visible? PROBLEM XIX. To represent a right sphere, a parallel sphere, and an oblique sphere. RULE. Bring the poles to coincide with the horizon, for a right sphere; bring the equator to coincide with the horizon, for a parallel sphere; and elevate one of the poles less than 90o above the horizon, for an oblique sphere. Note. When the globe is in the position of a right sphere, it will represent the situation of the earth at the time of the eqinoxes; when the north pole is elevated 231°, it will represent the situation of the earth at the time of the summer solstice; and when the south pole is elevated 234°, it will represent the situation of the earth at the time of the winter solstice.. PROBLEM XX. A place being given in the north frigid zone, to find the number of days on which the sun shines constantly, without setting, at that place, and the number of days he is totally absent. RULE Rectify the globe for the latitude of the place, and bring the ascending part of the ecliptic to the north point of the horizon; observe the degree of the ecliptic which cuts that point, and the day of the month answering to that degree on the calendar, shows the time when continual day begins. Bring the descending part of the ecliptic to the same point of the horizon, and observe the degree as before, the day on the calendar which answers to it, is that on which continual day ends, During the interval between these two days the sun shines constantly. To find when the longest night begins and ends, bring the descending and ascending parts of the ecliptic to the south, instead of the north point of the horizon. Find the length of the longest day and the longest night at - the following places : North Cape, in latitude 714° N. CELIFT I I 1. The Celestia Gate heavens, or in the ral situations 2. The Sua S their satelina w ant 3. The sun is gez a centre of our SEE A L in different per a i d The sur's demez: 22 JU ZUE days 14 hours é marette 4. Planets are age wie move round the BUL 5. The primary pares em t motion. Planets a the borzon: serve the fegree of the ecliptic which cuts that pout, mute my off ne month answering to that degree on the center, suws te me when continual day begins. Bring the evening part of the ecliptic to the same point of the burzon, mi iserve de degree as before, the day on the calentar vici answers at is dat in which continual day ends, During the interval between these two days the sun shines consancy. Ta ini when the longest night begins and ends, beng de descening and ascending parts of the ecliptic to the SPICA, DISKERİ furth point of the horizon. Find the length of the longest day and the longest night at the inlowing pinces — North Cape, in incicule 71° N. |