ASTRONOMY AND METEOROLOGY. 341 



explanation whicli was the foundation of the memorable law 

 announced by the German philosopher, Kirchhoff, in 1859 ; a law 

 now universally accepted as affording a perfect solution to the 

 long standing puzzle of Fraunhofer's lines. — Reader. 



BOLIDES. 



A bolide is a planet in miniature ; a small mass of matter, re- 

 volving round the sun in a longer or shortfer elliptical orbit, obey- 

 ing the same laws and governed by the same forces as the greater 

 planets. Now, suppose the orbit described by a bolide to cross 

 the orbit of the earth, exactly as one road crosses another ; and, 

 moreover, that the two travellers reach the point of junction or 

 crossing at the very same time. A collision is the inevitable con- 

 sequence. The bolide, which, in respect to size, is no more than 

 a pebble thrown against a railway train, will strike the e:irth with- 

 out lier inhabitants experiencing, generally, the slightest shock. 

 If individuals hapjjen to be hit, the case will be ditferent. If the 

 earth arrive there a, little before or after the bolide, but at a rela- 

 tively trifling distance, she will attract it, cause it to quit its own 

 orbit, dragging it after her, an o'bedient slave, to revolve around 

 her until it falls to her surface. Or it may happen that the liolide 

 may pass too far away for the earth to drag it into her clutches, 

 and yet near enough to make it swerve from its course. It may 

 even enter our atmosphere, and yet make its escape. But, in the 

 case of its entering the atmosphere, its friction against the air will 

 cause it to become luminous and hot, perhaps determining an ex- 

 plosion. Such are the meteors whose appearance at enormous 

 heights our newspapers record from time to time. 



lie it remarked that bolides are true planets, and not projectiles 

 shot out from niountains in the moon, as has been conjectured. A 

 projectile coming from the moon would reach the earth with a 

 velocity of about seven miles per second. But the most sluggish 

 bolide travels at the rate of nearly nineteen miles per second, fast 

 goers doing their six-tmd-thirty miles in the same short space of 

 time. None of the inferior planets travel so rapidly as that. Mer- 

 cury, the swiftest of them all, gets over only thirty miles per sec- 

 ond. Mr. Tyndall states that this enormous speed is certainly 

 competent to produce the eflects ascribed to it. 



When a bolide, then, glances sufficiently close to our earth to 

 pass through our atmosphere, the i-esulting friction makes its sur- 

 face red hot, and so rendei's it visible to us. The sudden rise of 

 temperature modifies its structure. The unequal expansion causes 

 it to exjjlode with a report which is audible. If the entire mass 

 does not burst, it at least throws off splinters and fragments. The 

 effect is the same as that j^roduced by pouring boiling water upon 

 glass. The fragments, falling to the ground, ai-e aerolites. It is 

 needless here to cite instances of their falling. They are of uni- 

 versal notoriety. Aerolites have no new suljstance to otl'er us. If 

 the earth, therefore, be made up of atoms, we may conclude that 

 the universe is made up of atoms. — All the Year Bound. 

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