Curiosities of Science, Past and Present: A Book for Old and YoungTimbs, John
Science
Curiosities of Science, Past and Present: A Book for Old and Young
Timbs, John
Science
The same astronomer saw at the Cape of Good Hope, on the 29th March
1837, a solar spot occupying an area of near _five square minutes_,
equal to 3,780,000,000 square miles. “The black centre of the spot of
May 25th, 1837 (not the tenth part of the preceding one), would have
allowed the globe of our earth to drop through it, leaving a thousand
miles clear of contact on all sides of that tremendous gulf.” For such
an amount of disturbance on the sun’s atmosphere, what reason can be
assigned?
The Rev. Mr. Dawes has invented a peculiar contrivance, by means of
which he has been enabled to scrutinise, under high magnifying power,
minute portions of the solar disc. He places a metallic screen, pierced
with a very small hole, in the focus of the telescope, where the image
of the sun is formed. A small portion only of the image is thus allowed
to pass through, so that it may be examined by the eye-piece without
inconveniencing the observer by heat or glare. By this arrangement,
Mr. Dawes has observed peculiarities in the constitution of the sun’s
surface which are discernible in no other way.
Before these observations, the dark spots seen on the sun’s surface
were supposed to be portions of the solid body of the sun, laid bare to
our view by those immense fluctuations in the luminous regions of its
atmosphere to which it appears to be subject. It now appears that these
dark portions are only an additional and inferior stratum of a very
feebly luminous or illuminated portion of the sun’s atmosphere. This
again in its turn Mr. Dawes has frequently seen pierced with a smaller
and usually much more rounded aperture, which would seem at last to
afford a view of the real solar surface of most intense blackness.
M. Schwabe, of Dessau, has discovered that the abundance or paucity
of spots displayed by the sun’s surface is subject to a law of
periodicity. This has been confirmed by M. Wolf, of Berne, who shows
that the period of these changes, from minimum to minimum, is 11 years
and 11-hundredths of a year, being exactly at the rate of nine periods
per century, the last year of each century being a year of minimum. It
is strongly corroborative of the correctness both of M. Wolf’s period
and also of the periodicity itself, that of all the instances of the
appearance of spots on the sun recorded in history, even before the
invention of the telescope, or of remarkable deficiencies in the sun’s
light, of which there are great numbers, only two are found to deviate
as much as two years from M. Wolf’s epochs. Sir William Herschel
observed that the presence or absence of spots had an influence on the
temperature of the seasons; his observations have been fully confirmed
by M. Wolf. And, from an examination of the chronicles of Zurich from
A.D. 1000 to A.D. 1800, he has come to the conclusion “that years rich
in solar spots are in general drier and more fruitful than those of an
opposite character; while the latter are wetter and more stormy than
the former.”
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