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HA'LO, n. s.

LONDON ENCYCLOPÆDIA.

A red circle round the sun or

moon.

If the hail be a little flatted, the light transmitted may grow so strong, at a little less distance than that of twenty-six degrees, as to form a halo about the sun or moon; which halo, as often as the hail-stones are Newton. duly figured, may be coloured.

I saw by reflection, in a vessel of stagnated water, three halos, crowns or rings of colours about the sun, like three little rainbows, concentrick to his body.

them saw his own shadow projected upon it, and
The distance was such that all the
no other.
parts of the shadow were easily distinguishable,
as the arms, the leg, and the head; but what
surprised them most was, that the head was
adorned with a kind of glory, consisting of three
or four small concentric crowns, of a very lively
color, each exhibiting all the varieties of the pri-
mary rainbow, and having the circle of red on
the outside. The intervals between these circles
continued equal, though the diameters of them
all were constantly changing. The last of them
was very faint; and at a considerable distance
was another great white circle, which surrounded
As near as M. Bouguer could com
the whole.
pute, the diameter of the first of these circles
was about 53°, that of the second 11°, that of the
third 17°, and so on; but the diameter of the
white circle was about 76°. This phenomenon
never appeared but in a cloud consisting of
frozen particles, and never in drops of rain like
the rainbow. When the sun was not in the ho-
rizon, only part of the white circle was visible,
as M. Bouguer frequently observed afterwards.
Similar to this curious appearance was one seen
by Dr. M'Fait in Scotland; who observed a
In this situa-
rainbow round his shadow in the mist, when he
was upon an eminence above it.
tion the whole country round seemed buried un-
der a vast deluge, and nothing but the tops of
distant hills appeared here and there above the
flood. In those upper regions, the air, he says,
is at that time very pure and agreeable. At
another time he observed a double range of co-
lors round his shadow. The colors of the outer-
most range were broad and very distinct, and
every where about two feet distant from the
shadow. Then there was a darkish interval,
and after that another narrower range of colors,
closely surrounding the shadow, which was very
much contracted. He thinks that these ranges
of colors are caused by the inflection of the
rays of light, the same that occasioned the ring
of light which surrounds the shadow of all bo-
dies, observed by M. Maraldi, and this author.

Halos may be produced by placing a lighted candle in the midst of steam in cold weather. If glass windows be breathed upon, and the flame of a candle be placed some feet from it, while the spectator is also at the distance of some feet from another part of a window, the flame will be surrounded with a colored halo. And if a candle be placed behind a glass receiver, when air is admitted into the vacuum within it, at a certain degree of density, the vapor with which it is loaded will make a colored halo round the flame. This was observed by Otto Guericke. In December 1756 M. Muschenbroeck observed, that, when the glass windows of his room were coverwith a thin plate of ice on the inside, the moon appearing through it was surrounded with

B

Id.

HALO, or Corona, in optics, is a luminous circle surrounding the sun, moon, planets, or fixed stars. Sometimes these circles are white, and sometimes colored like the rainbow. Sometimes one only is visible, and sometimes several concentric halos appear at the same time. Those which have been seen about Sirius and Jupiter were never more than 3°, 4°, or 5° in diameter; those which surround the moon are, also, sometimes no more than 3° or 5°; but these, as well as those which surround the sun, are of very different magnitudes, viz. of 12° 0′, 22° 35′, 30° 0', 38° 0′, 41° 2′, 45° 0′, 46° 24', 47° 0′, and 90°, Their diameters also or even larger than this. sometimes vary during the time of observation, and the breadths both of the colored and white circles are very different, viz of 2°, 4°, or 7°. Their colors are more diluted than those of the rainbow; and they are in a different order, according to their size. Mr. Huygens observed red next the sun, and a pale blue outwards. Sometimes they are red on the inside and white on the outside. M. Weidler observed one that was yellow on the inside and white on the outside. In France one was observed, in 1683, the middle of which was white; after which followed a border of red, next to it was blue, then green, and the outermost circle was a bright red. In 1728 one was seen of a pale red outwardly, then followed yellow, and then green, terminated by a white. In Holland, M. Muschenbroeck says, fifty may be seen in the day-time, almost every year; but they are difficult to be observed, except the eye be so situated, that not the body of the sun, but only the neighbouring Mr. Middleparts of the heavens, can be seen. ton says, that this phenomenon is very frequent in North America; for that there is generally one or two about the sun every week, and as Halos many about the moon every month. M. round the sun are very frequent in Russia. Epinus says, that from the 23d of April, 1758, to the 20th of September, he himself had observed no fewer than twenty-six, and that he has sometimes of time. seen twice as many in the same space Similar, in some respects, to the halo, was the remarkable appearance which M. Bouguer describes, as observed on the top of Mount Pichinca, in the Cordilleras. When the sun was just ris-ed ing behind them, so as to appear white, each of VOL. XI.-PART I.

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LONDON ENCYCLOPÆDIA.

HA'LO, n. s. A red circle round the sun or

moon.

If the hail be a little flatted, the light transmitted may grow so strong, at a little less distance than that of twenty-six degrees, as to form a halo about the sun or moon; which halo, as often as the hail-stones are duly figured, may be coloured. Newton.

I saw by reflection, in a vessel of stagnated water, three halos, crowns or rings of colours about the sun, like three little rainbows, concentrick to his body.

them saw his own shadow projected upon it, and
no other.
The distance was such that all the
parts of the shadow were easily distinguishable,
as the arms, the leg, and the head; but what
surprised them most was, that the head was
adorned with a kind of glory, consisting of three
or four small concentric crowns, of a very lively
color, each exhibiting all the varieties of the pri-
mary rainbow, and having the circle of red on
the outside. The intervals between these circles
continued equal, though the diameters of them
all were constantly changing. The last of them
was very faint; and at a considerable distance
was another great white circle, which surrounded
the whole. As near as M. Bouguer could com
pute, the diameter of the first of these circles
was about 53°, that of the second 11°, that of the
third 17°, and so on; but the diameter of the
white circle was about 76°. This phenomenon
never appeared but in a cloud consisting of
frozen particles, and never in drops of rain like
the rainbow. When the sun was not in the ho-
rizon, only part of the white circle was visible,
as M. Bouguer frequently observed afterwards.
Similar to this curious appearance was one seen
by Dr. M'Fait in Scotland; who observed a
rainbow round his shadow in the mist, when he
was upon an eminence above it. In this situa-
tion the whole country round seemed buried un-
der a vast deluge, and nothing but the tops of
distant hills appeared here and there above the
flood. In those upper regions, the air, he says,
is at that time very pure and agreeable. At
another time he observed a double range of co-
lors round his shadow. The colors of the outer-
most range were broad and very distinct, and
every where about two feet distant from the
shadow. Then there was a darkish interval,
and after that another narrower range of colors,
closely surrounding the shadow, which was very
much contracted. He thinks that these ranges
of colors are caused by the inflection of the
rays of light, the same that occasioned the ring
of light which surrounds the shadow of all bo-
dies, observed by M. Maraldi, and this author.

Halos may be produced by placing a lighted candle in the midst of steam in cold weather. If glass windows be breathed upon, and the flame of a candle be placed some feet from it, while the spectator is also at the distance of some feet from another part of a window, the flame will be surrounded with a colored halo. And if a candle be placed behind a glass receiver, when air is admitted into the vacuum within it, at a certain degree of density, the vapor with which it is loaded will make a colored halo round the flame. This was observed by Otto Guericke. In December 1756 M. Muschenbroeck observed, that, when the glass windows of his room were coverwith a thin plate of ice on the inside, the moon appearing through it was surrounded with

B

Id.

HALO, or Corona, in optics, is a luminous circle surrounding the sun, moon, planets, or fixed stars. Sometimes these circles are white, and sometimes colored like the rainbow. Sometimes one only is visible, and sometimes several concentric halos appear at the same time. Those which have been seen about Sirius and Jupiter were never more than 3°, 4°, or 5° in diameter; those which surround the moon are, also, sometimes no more than 3° or 5°; but these, as well as those which surround the sun, are of very different magnitudes, viz. of 12° 0′, 22° 35′, 30° 0', 38° 0′, 41° 2′, 45° 0′, 46° 24′, 47° 0′, and 90°, or even larger than this. Their diameters also sometimes vary during the time of observation, and the breadths both of the colored and white circles are very different, viz of 2°, 4°, or 7°. Their colors are more diluted than those of the rainbow; and they are in a different order, according to their size. Mr. Huygens observed red next the sun, and a pale blue outwards. Sometimes they are red on the inside and white on the outside. M. Weidler observed one that was yellow on the inside and white on the outside. In France one was observed, in 1683, the middle of which was white; after which followed a border of red, next to it was blue, then green, and the outermost circle was a bright red. In 1728 one was seen of a pale red outwardly, then followed yellow, and then green, terminated by a white. In Holland, M. Muschenbroeck says, fifty may be seen in the day-time, almost every year; but they are difficult to be observed, except the eye be so situated, that not the body of the sun, but only the neighbouring parts of the heavens, can be seen. Mr. Middleton says, that this phenomenon is very frequent in North America; for that there is generally one or two about the sun every week, and as many about the moon every month. Halos round the sun are very frequent in Russia. M. Æpinus says, that from the 23d of April, 1758, to the 20th of September, he himself had observed no fewer than twenty-six, and that he has sometimes seen twice as many in the same space of time.

Similar, in some respects, to the halo, was the remarkable appearance which M. Bouguer describes, as observed on the top of Mount Pichinca, in the Cordilleras. When the sun was just ris-ed ing behind them, so as to appear white, each of VOL. XI.-PART I,

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