00000351 |
Previous | 351 of 595 | Next |
|
small (250x250 max)
medium (500x500 max)
Large
Extra Large
large ( > 500x500)
Full Resolution
All (PDF)
|
320
THE ATMOSPHERE AND METEOROLOGY.
gradually became more numerous till 1728, and then diminished. In 1755
they were of very rare occurrence, but became more and more frequent
toward the end ofthe century; in 1812 they were again at a minimum*;
but from the year 1825 they increased in number very rapidly, the average rising from one per annum to thirty and forty in the same space of
time. It would appear, from the discussion of these facts, that the cycle
of auroras is one of fifty-eight, fifty-nine, or sixty years, and perhaps this
period may itself be divided into six periods of ten years, corresponding,
as Schwabe observes, with the regular variations of similar duration noticed in the number and size of the sun-spots; thus the fluctuations of the
magnetic storms constitute an astronomical phenomenon. The accompanying figure represents the series of auroras seen at New Haven, in Connecticut, during the seventy years from 1785 to 1854, comprising an entire
period.
fivuahers
So-
43-
40-
35-
30-
20-
15-
10-
B-
s Years 1J84 1394' 180* lfll% 1S2% 183% 18i%. l^a
Fig. 147.—Auroras observed at New Haven, Connecticut, United States, 1784-1854.
It is difficult to explain'now why the aurora appears more frequently
in certain places of the Old and New World than in other parts situated
at an equal distance from the magnetic pole. But it is incontestable that
this latter point is not distant from the centre whence the auroral light
radiates. In our hemisphere the culminating point of the luminous arc is
found toward the direction of the peninsula of Boothia Felix, where Ross
saw the southern pole of the magnetic needle turn directly toward the
centre ofthe earth. In Norway one sees the aurora borealis in the northwest; in Greenland, directly to the west; at Melville Island, Parry viewed
it on the southern horizon. It must not be thought, however, that these
magnetic storms are very frequent in the high circumpolar regions; on
the contrary, they are rather rare there, to judge from the accounts of
travelers who have advanced farthest to the north. Hayes, during his
stay in Smith's Strait, only saw three phenomena of this kind. In this
northern space, which is destitute of auroras—that is, in Southern Green-
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000351 |
| Type | Books/Pamphlets |
| Transcript | 320 THE ATMOSPHERE AND METEOROLOGY. gradually became more numerous till 1728, and then diminished. In 1755 they were of very rare occurrence, but became more and more frequent toward the end ofthe century; in 1812 they were again at a minimum*; but from the year 1825 they increased in number very rapidly, the average rising from one per annum to thirty and forty in the same space of time. It would appear, from the discussion of these facts, that the cycle of auroras is one of fifty-eight, fifty-nine, or sixty years, and perhaps this period may itself be divided into six periods of ten years, corresponding, as Schwabe observes, with the regular variations of similar duration noticed in the number and size of the sun-spots; thus the fluctuations of the magnetic storms constitute an astronomical phenomenon. The accompanying figure represents the series of auroras seen at New Haven, in Connecticut, during the seventy years from 1785 to 1854, comprising an entire period. fivuahers So- 43- 40- 35- 30- 20- 15- 10- B- s Years 1J84 1394' 180* lfll% 1S2% 183% 18i%. l^a Fig. 147.—Auroras observed at New Haven, Connecticut, United States, 1784-1854. It is difficult to explain'now why the aurora appears more frequently in certain places of the Old and New World than in other parts situated at an equal distance from the magnetic pole. But it is incontestable that this latter point is not distant from the centre whence the auroral light radiates. In our hemisphere the culminating point of the luminous arc is found toward the direction of the peninsula of Boothia Felix, where Ross saw the southern pole of the magnetic needle turn directly toward the centre ofthe earth. In Norway one sees the aurora borealis in the northwest; in Greenland, directly to the west; at Melville Island, Parry viewed it on the southern horizon. It must not be thought, however, that these magnetic storms are very frequent in the high circumpolar regions; on the contrary, they are rather rare there, to judge from the accounts of travelers who have advanced farthest to the north. Hayes, during his stay in Smith's Strait, only saw three phenomena of this kind. In this northern space, which is destitute of auroras—that is, in Southern Green- |
|
|
|
|
|
|
| B |
|
| C |
|
| G |
|
| H |
|
| M |
|
| T |
|
| U |
|
| Y |
|
|
|
