2. Elevate the pole, which is of the same name as the declination, as many degrees as are equal to it?

When the globe is rectified for the sun's place, and the sun brought to the zenith, the horizon will be the terminator, or boundary circle of light and darkness; it will therefore be day with all those places that are above the horizon, and night with all those that are below it.

EXAMPLES.

1. Rectify the globe for the sun's place on June 4th. Answ. On June 4th the sun's declination is 22° N.; therefore the north pole must be elevated 224° above the horizon.

2. Elevate the globe for the sun's place on October 6th. Answ. The sun's declination on October 6th is 5° S.; hence the south pole must be elevated 5° above the horizon.

PROBLEM XVIII.

To find the sun's rising and setting for any given day, at any given place.

1. Elevate the globe for the sun's declination, bring the given place to the meridian, and set the index to 12.

2. Turn the globe till the given place come to the eastern edge of the horizon, and the index will show the time of. the sun's rising.

3. Bring the given place to the western edge of the horizon, and the index will show the time of the sun's setting.

If the hour circle have a double row of figures, make use of that which increases towards the east; the sun's rising and setting may then be found at once, by bringing the place only to the eastern edge of the horizon, for the index will point in one row to the hour of rising, and on the other (that which increases towards the west) to the hour of setting.

This problem may also be performed in the following manner. 1. Elevate the globe for the latitude of the place, bring the sun's place to the meridian, and set the index to 12. 2. Bring the sun's place to the eastern horizon, and the index will show the time of the sun's rising.

3. Bring it to the western edge of the horizon, and the index will show the time of setting.

BY ADAMS'S GLOBES.

Having elevated the globe for the sun's declination, brought the given place to the meridian, and set the index to 12 as before,-bring the given place to the western edge of the horizon, and the index will show the time of the sun's rising; bring it to the eastern edge, and the index will show the time of setting.

By this problem may be found the length of the day and night. RULE.-1. Double the time of the sun's setting, and it will give the length of the day.

2. Double the time of the sun's rising, and it will give the length of the night.

In White's Ephemeris, pages 40 to 43, is given a table of the sun's semidiurnal arcs, or time of its half visible duration above the horizon, by which may be found the time of the sun's rising or setting in any part of Great Britain or Ireland.

As this method is very easy, and may be of use, either to prove the method by the globes, or where a pair of globes is wanting, it is here inserted.

Find the declination in the Ephemeris, for the given day. On that page which is marked N. or S. according as the declination is N. or S. look down the left-hand column, marked degrees at the top, till you come to that degree which is equal to the sun's declination; then look for the latitude of the place at the top of the table, and, in that column against the sun's declination, will be found the time of its visible half

duration above the horizon: this is its time of setting. Subtract this from 12, and the remainder will be the time of rising.

This method will give the time of the sun's rising and setting to within a few minutes; but if the latitude of the place, and the sun's declination, consist of degrees and minutes, and if greater accuracy be required, a small allowance must be made for the minutes, in both cases, in the following manner.

Find the nearest proportional part that the odd minutes are of one degree, and, first for the latitude, take the same proportional part of the difference between the column marked latitude and the next one.

For the odd minutes of the declination, take the proportional part of the difference between the degrees of declination and the next one. These two differences, added to the semidiurnal, are found in the table, when the sun's declination is north, but subtracted from it, when the sun's declination is south, will give the time of the sun's setting to a minute.

EXAMPLES.

1. Required the time of sun-rise and sun-set at Edinburgh on the 1st of June.

Answ. The sun rises at 27 minutes after 3, and sets 33 minutes after 8.

2. What time does the sun rise and set at London on July 17th, and what is the length of the day and night? Answ. The sun rises at 4, and sets at 8; the length of the day is 16 hours, and the night 8 hours.

Required the rising and setting of the sun at the following places, on the respective days mentioned.

3. Pekin, April 10.

4. Newcastle, Oct. 13.

5. Gibraltar, Jan. 22.

6. Petersburg, June 21.

7. Hamburgh, Dec. 21.

8. North Cape, Dec. 21.

9. Botany Bay, May 25. 10. London, Aug. 29.

Required the rising and setting of the sun at Cape Horn,

on the following days:

11. January 29.

12. March 2.

Required the time of the sun's rising and setting at Edin

burgh, on the following days.

29. Required the time of the sun's rising and setting at the following places, on March 21st and September 28d:— Archangel, London, Vienna, Jerusalem, Quito, and the Cape of Good Hope.

What is the length of the longest and shortest day, at the following places, and what is the difference between them?

What is the length of the day, and of the night, on December 26th, at the following places?

46. Dresden.

47. Turin.

48. Adrianople.

49. Shiraz.

50. Medina.

51. What is the hour of the sun's rising at Pekin, Naples, and Philadelphia, on August 29th?

52. How much longer is the sun above the horizon, on June 21st, to Edinburgh than to London?

53. How much longer is June 21st at Petersburgh, than at Jerusalem?

54. At what time does the sun rise and set at Spitzbergen, on April 5th?

EXAMPLES.

of finding the sun's rising and setting in any part of GreatBritain or Ireland, by White's Ephemeris.

1. What is the hour of the sun's rising and setting at Newcastle, on May 31st?

The sun's declination on that day is 22° N. and the latitude of Newcastle is 55°. Look down the left-hand column of page 42d of the Ephemeris for 22; then against 22, in the column marked at the top latitude 55, stands 8 hrs. 26 min.-which is the time of the sun's setting on that day; and this, subtracted from 12, gives 3 hrs. 34 min. the time of rising.

2. Required the sun's rising and setting at Liverpool, on May 14.

The latitude of Liverpool is 53° 22′, and the sun's declination for May 14th is 18° 28′ N. Neglecting the minutes, look in page 40 for the declination, 18 degrees: then against that degree, in the column marked latitude 53, stands 7 hrs. 46 min. the time of the sun's setting on that day. If greater accuracy be required, the minutes may be allowed for thus-on the line of 18° take the difference between the columns 53 and 54, which is 5 minutes: then 22' being rather more than the third part of 60, 2 minutes of time may be allowed for it. For the odd minutes of declination (28), nearly equal half a degree, take half the difference of the hours and minutes in the column (latitude 53) standing against the respective lines 18 and 19; the difference in the present case is 7 minutes, -the half of which may be called 3. Hence, adding 2 minutes of time for the odd minutes of latitude, and 3 for the declination, the time of the sun's setting, on the above day, will be 7 hrs. 51 min.

It may be proper here to observe, that, without allowing for the minutes of latitude or declination, the table will give the sun's setting to