apparent daily course of any heavenly body. In latitude 85°, for instance, the sun, which, at midnight of the 3d of April, touches the northern horizon, obtains an elevation of ten degrees only in proceeding from the north to the south during the succeeding twelve hours; such being his altitude when greatest, or at noon of that date. At the pole itself, where the inhabitants, if any, have a parallel sphere, (the equinoctial line describing their rational horizon,)* the place of the sun in the sphere, when he has not too great south declination, must, for weeks, be traceable, first by the point of strongest twilight, then by the point of most vivid redness, which will appear to traverse the whole horizon each twenty-four hours as the scenery rotates around the observer. When the sun's north limb (the upper portion of his circumference) first shows itself, (in consequence of refraction some days before the 21st of March,) it is gliding thus along in the course of a few hours this floating segment of his disk visibly increases; then his centre appears; then his whole form: and thus he continues to ascend, in a course really spiral, but not perceptibly so, until, on the 21st of June, three months from his rising, he has attained his greatest altitude of 23° 28' by attaining his greatest north declination; again to descend during three months, (21st of June to 23d of September,) by the same spiral course, to the equinoctial in the horizon.

:

PROBLEM X.

CELESTIAL GLOBE.

Having a latitude within the north Frigid Zone, to find the length of the period of the continual presence or absence of the sun; and to note some of the phenomena of the heavens during those periods.

* At the poles, the distinction of east and west could not obtain, the whole horizon being to the south, and the polar point in the zenith.

PHENOMENA OF THE FRIGID ZONES.

Read over and explain the remarks on pp. 130-132.

133

RULE.—1. Elevate the pole to the latitude, and mark the two points in the ecliptic which are cut by the brazen meridian in the north point of the horizon: the day answering to that point of the ecliptic in which the sun is coming northward, is the day of the commencement of the long period of sun-light; and the interval between this day and the day answering to the other point, will give that period. 2. Note the two points of the ecliptic which are cut in like manner by the south point of the horizon, and the interval between the two corresponding days, reckoning from that on which the sun is going southward, will give the period of his long absence.

*** The quadrant of altitude fixed in the zenith, will measure altitudes and depressions as before. It must be remembered that the sun, whether above the horizon or below it, is always crossing the south of the meridian at noon, and the north of it at midnight.

Observe, the sun must be 18° depressed in order that stars of the sixth magnitude (and therefore the whole) may be seen at their rising or setting.

Stars of the 1st magnitude may appear at their rising or setting when he is depressed

of the 2d

of the 3d

12°

13°
14° &c.

1. Messrs. Scoresby, in 1806, attained the latitude of 8150 N. On what days does the sun there begin and end his visit of longest continuance; and how long might Messrs. Scoresby have viewed the sun continually above the horizon, had their avocations permitted their stay in that latitude?

2. What are the different altitudes of the sun at the following hours of the following dates in latitude 82° 40', attained by Captain Parry in his attempt to reach the pole across the ice during June and July, 1827?

N

Viz. 3d of June

At midnight,(a) at 4 л. м. and 10 a. M.
At noon, at 2 P. M. and 8 P. M.(b)

22d of August, at 6 л. м. and at 6 P. M.

The "fields" of ice are formed on the surface of the sea, and are the congelation of salt water. Icebergs which are the accumulated productions of centuries, and which sometimes attain the altitude of a thousand feet before they float, are formed near the cliffs of the shores, entirely from the fresh water, which proceeds in torrents from the meltings of the snow during the periods of the long presence of the sun. In the journey of Captain Parry, referred to above, he failed to reach the 83°. He found, on taking his observations, that the vast covering of the ocean over which he was travelling, was drifting daily faster southward than his party could traverse it towards the north.

3. In 1754, Mr. Stephens is said to have reached lat. 8410. How long (without considering the effect of refraction) does the sun continue above the horizon in that latitude?

It is commonly during June that the vast shoals of ice formed from sea-water, are broken up: they are not dispersed and dissolved, (even where the locality admits of it,) until the end of that month. A dense fog then generally rests, for some weeks, on the sea-surface; the higher land alone being exposed to the sun-beams. When this fog disperses, the heat, which has been accumulating during so many weeks from the continuous though slanting rays of the sun, is so intense as to cause the pitch to run down the sides of vessels.

CAPTAIN PARRY'S FIRST VOYAGE, A.D., 1819.

Melville Island, lat. 7430, November 11. "Mr. Ross, having gone to the mast-head at noon, reported that he saw the sun.

On the following day we expected to see the sun again, and looked out from the mast-head for that purpose, but he did not re-appear." (page 115).

4. Refraction caused his appearance as described above, at noon of the 11th of November. How far (c) was the sun really depressed at noon on that day in that latitude?

(a) To avoid the stronger snow-glare, and to ensure the greater dryness of the ice, Captain Parry's party dined at midnight, travelling during five or six hours before and after that hour; and availing themselves of the greater portion of warmth, when the sun was higher, for resting and sleeping.

(b) At 2 P. M., the same as at 10 A. M., &c.

(c) The thickness of the wooden horizon will render it awkward to examine that portion of the ecliptic in which the sun is situated: to answer this question, therefore, find the sun's declination, and contrast it with the declination in the south point of the horizon or the

co-latitude.

CAPTAIN PARRY'S VOYAGES.

135

Nov. 17. "At noon to day we saw, for the first time at this hour, a star of the first magnitude (Capella); and, at half an hour past noon, those of the second magnitude in Ursa Major, were visible." (p. 116.)

5. What was the sun's depression at noon of Nov. 17?(d) 6. What were the azimuth and altitude of Capella, and of Arcturus; and why was Arcturus not then seen as well as Capella?(e)

February 3d. "At twenty minutes before apparent noon, the sun was seen from the Hecla's main-top, (fifty-one feet above the sea,) being the first time that this luminary had been visible to us since the 11th of November, a period of eighty-four days; or--days less than the time of its remaining actually beneath the horizon, independently of the effects of atmospherical refraction.”—(p. 139.)

7. On what day would the sun have re-appeared (ƒ) had there been no refraction; and on how many additional days have the inhabitants of that latitude the advantage of a portion of sun-light in consequence of this beautiful arrangement of Divine providence, which rendered the sun visible on the 3d of February? (g)

"A column of light had been observed by Captain Sabine, (on this day, 3d of February,) at 10 A. M., immediately over the spot where the sun was."-(p. 139.)

8. Give the depression of the sun at that time, and the point of the horizon in which this column of light appeared?

CAPTAIN PARRY'S SECOND VOYAGE, A.D., 1821.

Winter Island, where Captain Parry's ships were blocked up during the winter-months of 1821, is in lat. 6610, (not quite within the Arctic circle.) He had three hours daylight, for writing in the cabin, on the 21st of December.

Igloolik, lat. 6910, Dec. 2, 1822. "At apparent noon, days after the sun had, independently of the effects of refraction, set to us for a period of more than weeks, we caught a glimpse of its upper limb from the deck of the Fury.”—(p. 383.)

(d) See note (c).

(e) Consider how it was that one of these stars was, at this hour, involved in strong twilight.

(f) i. e., when, after his long absence, did he again attain declination corresponding to the co-latitude.

(g) The days of his appearance by refraction, after he has really ceased to rise, (viz., at the beginning of their long winter period,) are as many as those found here; hence we must double the number of days to answer the question.

Jan. 5, 1823. "The sky looked so red towards noon, that we were induced to look out for the sun from the mast-head, but without success, though we could not help fancying every moment, that it was about to burst above the horizon."

9. Find the length of the long period of the sun's absence at Igloolik, and also the days during which he is constantly above the horizon there.

CAPTAIN PARRY'S THIRD VOYAGE, 1824, 1825.

Port Bowen, lat. 7310. "As early as the 20th of November, Arcturus could very plainly be distinguished by the naked eye, when near the south meridian at noon."

10. Find the altitudes and azimuths of Spica Virginis, Regulus, Castor, and Capella, and of a of Lyra and Altair, at Port Bowen, at noon of the 20th of November; and, since Arcturus could be thus distinguished at noon, show why certain of these several stars might or might not also be discernible? (h)

11. The most remarkable of all the stars has declination very nearly corresponding to the co-latitude of Port Bowen; and, consequently, is visible in the south point of the horizon, when culminating in that latitude; at what hour does this take place on the 20th of November, and is the depression of the sun then such as to admit of this star's being seen?(i)

12. What declination must the sun have, in order that his twenty-four hours' course at Port Bowen, may be exactly similar to that of Aldebaran; and on what two days of the year does this occur ?

13. What is the greatest depression of B Leonis at Port Bowen ?

14. In what latitude is the course of Arcturus nearly similar to that of Aldebaran at Port Bowen ;(k) and what is the length of the sun's long period in that latitude?

(h) One of these stars was too near the horizon and the twilight; others of them were more favourably situated than Arcturus. (i) See the observation at the end of the rule.

(k) i. e., in what latitude does the northern, or "lower culmination" of Arcturus, just touch the horizon?