CHAMBERS'S INFORMATION FOR THE PEOPLE. 



LUMINOUS METEORS. 

 Rainbows Halos Parhelia Coronae, && 



The various luminous appearances of the 

 heavens, apart from the ordinary phenomena of 

 sun, moon, and star light, are usually treated of 

 under Meteorology. 



The rainbow is owing to a complicated reflec- 

 tion and decomposition of the rays of the sun in 

 passing through drops of rain. It appears when 

 the sun is unclouded, and rain is falling in the 

 opposite quarter of the heavens. The mode of its 

 formation is more particularly explained under 

 OPTICS. A morning rainbow is an unfavourable 

 prognostic of the weather ; a rainbow in the 

 evening is favourable. 



Halos are coloured rings occasionally seen sur- 

 rounding the sun or the moon. There are often 

 several circles, some concentric, others intersecting 

 or touching one another. They arise from the 

 minute snow crystals of the cirrus cloud, and are 

 due partly to refraction and partly to reflection. 

 It can be shewn by the well-known principles of 

 prismatic refraction, that the common halo of 22 

 radius is owing to refraction by the faces of the 

 crystals that are inclined to one another at an 

 angle of 60 ; while the wider circle of 46 radius 

 is produced by faces at an angle of 90. At cer- 

 tain points of the circles, other effects conspire to 

 produce luminous knots called parhelia (mock- 

 suns), or paraselenes (mock-moons). 



The true halos are to be distinguished from the 

 corona that surround the sun or moon when a 

 thin cloud passes over them. These depend on a 

 different optical principle. The same appearances 

 may be seen by looking at a candle through steam 

 or through the dust of a room. The smaller the 

 size of the particles, the greater is the diameter of 

 the corona. A narrowing corona round the moon 

 shews that the cloud particles are enlarging, and 

 indicates coming rain. Coronas are less often 

 seen round the sun, owing to the strength of his 

 light. 



One marked distinction between coronas and 

 halos is, that in halos the red prismatic colour is 

 next the centre ; in coronas, the blue. 



IGNEOUS METEORS. 

 Shooting-stars Fire-balls Aerolites. 



Shooting-stars are observed during serene nights. 

 A luminous point like a star bursts into view, 

 shoots a certain way through space, and then 

 disappears. Sometimes it leaves a luminous train 

 behind it ; in other cases it gives forth sparks. 

 These meteors have been noticed to occur in great 

 numbers at once ; and the interest of such appear- 

 ances has been very much increased by the fact 

 of their being in some measure periodical. On 

 several years they have been found to occur in the 

 month of November. They also occur with some 

 degree of frequency in August. Shooting-stars 

 and fire-balls break out occasionally at every 

 period of the year. 



It is now agreed that these bodies are nothing 

 else than small planets, and, therefore, the con- 

 sideration of them properly belongs to astronomy. 

 There is every reason to believe that the planets, 

 satellites, and comets are not the only bodies 



48 



, which move round the sun, and lie within the solar 

 system they are merely the large conspicuous 

 masses; while millions of others may exist, too 

 small to be descried on ordinary occasions, and 

 making themselves known by coming within the 

 earth's atmosphere. The friction against the air, 

 caused by their immense velocity, develops enor- 

 mous heat, which melts the surface of the body, 

 and this outer liquid portion is thrown off in a 

 long flaming stream forming the train, which, after 

 losing its velocity, is precipitated to the earth as a 

 fine dust or volcanic ash, while the meteor, thus, 

 rapidly diminishing, either becomes wholly dissi- 

 pated into tail, or falls to the earth, or makes its 

 way out of the atmosphere, and continues its- 

 course. The periodic meteors are small bodies : 

 they have been calculated to range from 30 grains 

 to 7 or 8 pounds, and none of them have been 

 known to fall to the earth. These smaller bodies,, 

 that are for the most part dissipated in the air, 

 are the shooting-stars, properly so called. The 

 irregular or sporadic meteors frequently come to- 

 the earth in large masses, and often burst in fall- 

 ing, owing to the outside being suddenly and 

 intensely heated, while the interior remains cold. 

 These aerolites (Gr. aer, air, and lithos, a stone)- 

 are found to consist of iron and stony matter 

 in various proportions, the iron in some largely 

 predominating. To account for the periodicity of 

 the November meteors, it is imagined that a great 

 number of them may move in a continuous ring or 

 common orbit round the sun, so situated that the 

 earth, in its annual course, brushes, as it were, 

 with the outskirts of its atmosphere this ring of 

 planetary fragments once a year. If the bodies 

 were all round the ring, there ought to be a shower 

 of them every November; but the great displays 

 occur only once in about 33 years; and there- 

 fore it is inferred that the great mass of them are 

 grouped at one part, and that the time of revolu- 

 tion of the ring being 33 years, that length of time 

 must elapse between each concurrence of the earth 

 and the dense part of the group. 



One of the most familiar of luminous meteors 

 is the ignis-fatuus, or ' Will-o'-the-wisp,' which 

 appears at night on marshy grounds, places of 

 sepulture, or wherever putrefaction and decompo- 

 sition are going on. The appearance is that of a 

 small flickering light, straggling in an irregular 

 manner at the height of one or two feet from the 

 ground, and sometimes standing for a few moments 

 over a particular spot. When approached or pur- 

 sued, the lights are agitated by the motion of the 

 air, and seem to elude investigation. The cause 

 of this species of meteor has never been satisfac- 

 torily explained. 



Until recently, meteorological observations had 

 been mostly casual and without any uniform plan ;. 

 hence the vagueness and uncertainty that hang 



1 over so much of the subject. But since 1840, the 

 earth has been covered with a net-work of mete- 

 orological observatories, maintained by the seve- 

 ral European governments. Above all, the use of 

 the telegraph in meteorology is proving a power- 

 ful means both of advancing the science and of 

 turning it to practical account. It is not un- 

 reasonable to anticipate that, with the agents and 

 apparatus now at work in this field, the next half- 

 century may see light and order arising out of 

 many things that now seem nothing but chaos. 



