CHAMBERS'S INFORMATION FOR THE PEOPLE. 



owing to its small size, has been dissipated into 

 space. 



The Moon and the Weather. -It is an almost 

 universal belief that the changes of the moon 

 influence the weather; but when put to the test 

 of accurate observation, this opinion is found to be 

 completely groundless : there is, in fact, no cor- 

 respondence whatever between the changes of the 

 moon and those of the weather. See METEOR- 

 OLOGY. 



ECLIPSES. 



Eclipses are caused by the positions of the earth 

 and moon with respect to each other and to the 

 sun. An eclipse of the sun takes place when the 

 moon is between the sun and earth ; and an 



eclipse of the moon is the result of the earth being 

 between the sun and moon. 



The accompanying figure represents two posi- 

 tions of the moon : in the one she is in the earth's 

 shadow, and totally eclipsed ; in the other, her 

 shadow is falling upon a part of the earth's surface, 

 and eclipsing the sun to that part. Within the 

 limited circle on which the moon's shadow, or 

 umbra, falls, no part of the sun is seen, or he is 

 in total eclipse ; within a larger space round that 

 spot, the moon seems to cover only part of the 

 sun's disk, making a partial eclipse ; and this 

 space is within the penumbra, as it is called. 

 When the moon happens to be so far distant from 

 the earth that the cone of the shadow falls short 

 of the earth, then a spectator standing immediately 

 under the apex, or point, sees the moon covering 



the middle part of the sun's disk, and leaving a 

 ring of it visible. This is an annular eclipse. 



It is only when the moon is in one of her nodes, 

 or within a limited distance from it, that there can 

 be an eclipse either of sun or moon. Now, the 

 motions of the two orbs are such that there must 

 be annually two solar eclipses, and there may be 

 four. The limits for a lunar eclipse are shorter, 

 and a whole year may elapse without one occur- 

 ring. There are thus more solar eclipses than 

 lunar, though the general impression is to the 

 contrary. This arises from the circumstance that, 

 whenever an eclipse of the moon occurs, it is seen 

 at all places where the moon is above the horizon, 

 and the atmosphere unclouded ; whereas an eclipse 

 of the sun is confined to a limited tract. 



These eclipses, like all other things about the 

 heavens, can be predicted with almost perfect 

 accuracy. It is also possible to calculate 

 backwards, so as to find the probable date of 

 remarkable eclipses recorded to have happened 

 in antiquity. 



The inferior planets, Mercury and Venus, some- 

 times cross the sun's face, on which occasion they 

 may be traced by a telescope as a dark speck 

 moving from one edge over to another, and then 

 disappearing. These are transits, and are of 

 importance in ascertaining the sun's parallax and 

 distance. 



In times when people's fates and fortunes were 

 predicted from the positions of the planets at the 

 hour of their birth, much stress was put upon 

 conjunctions and oppositions. When two bodies 

 are in the same quarter of the heavens, so as to 

 be near one another, or have the same longitude, 

 they are said to be in conjunction; when they are 

 half a circle apart in longitude, they are in opposi- 

 tion. Astronomers use the sign Q" to indicate con- 

 junction ; and to indicate opposition. 



COMETS. 



' Comets,' says Humboldt, ' at the same time 



possess the smallest mass, and occupy the largest 



space of any bodies in the solar regions ; in their 



number, also, they exceed all other planetary 



12 



bodies, except, perhaps, aerolites, amounting to 

 many thousands at least.' Comets have usually 

 two parts a body or head, and a tail. The head 

 has the appearance of a round nebulous mass of 

 light, with usually a brighter part in the centre 

 called the nucleus, but so far from containing any- 

 thing solid, that the smallest stars are seen through 

 the densest part of the substance. The tail is a 

 still lighter luminous vapour, surrounding the 

 body, and streaming far from it in a direction 

 generally opposite to that in which the sun is 

 situated, as if repelled by that luminary, and often 

 curved. A vacant space has been observed 

 between the body and the enveloping matter of 

 the tail, which also appears sometimes less bright 

 along the middle, immediately behind the head, 

 as if it were a stream which the head had parted 

 in two. 



Unlike planets, comets shine partly, at least, by 

 their own light, and are believed by some to be 

 masses of white-hot gas. Others suggest a connec- 

 tion between comets and the rings of small bodies 

 that produce meteoric showers (see METEOR- 

 OLOGY). The tail is by no means essential to a 

 comet ; by far the greater number have no such 

 appendage, appearing merely as a nebulous disk. 



With regard to the motions of the comets, 

 instead of revolving, like the planets, nearly in 

 the plane of the sun's equator, it is found that 

 they approach his body from all parts of sur- 

 rounding space. At first, they are seen slowly 

 advancing, with a comparatively faint appearance. 

 As they approach the sun, the motion becomes 

 quicker, and at length they pass round him with 

 very great rapidity, and at a comparatively small 

 distance from his body. The comet of 1843 

 approached within one-seventh of his radius. 

 When near the sun, their brilliancy is greatly 

 increased. 



In moving round the sun, comets obey the same 

 general laws that regulate the planets. They do 

 not, however, all describe ellipses ; some pass 

 through our system in parabolas, open curves, 

 which never return into themselves. Now, the 

 comets that move in shut orbits, or ellipses, 

 must return to the sun again and again, and may 



