230 IN STARRY REALMS. 



astronomical work, will frequently find a bright streak 

 of light flash across his field. This is a meteor, and a 

 comparison with any stars which may happen to be in the 

 field of view will probably show him that the object was 

 far too small to have been seen with the naked eye. We 

 must remember that the field of view of a large telescope 

 is but an extremely small fraction of the entire extent of 

 the heavens. It would be easy to show, by the doctrine 

 of chances, that if a telescopic shooting star were to dive 

 to extinction into the air, the chance against its being 

 seen by any particular telescope at that moment directed 

 to the sky would be at least fifty thousand to one ; but 

 every astronomer knows that the perception of a tele- 

 scopic shooting star is a common incident in the obser- 

 vatory. If, therefore, we reflect that for every one that 

 is seen there must be thousands which dart in unseen, we 

 obtain an imposing idea of the myriads of shooting stars 

 that daily rain in upon our globe. 



The world is thus pelted on all sides day and night, 

 year after year, century after century, by troops and 

 battalions of shooting stars of every size, from objects not 

 much larger than grains of sand up to mighty masses 

 which can only be expressed in tons. In the lapse of 

 ages our globe must thus be gradually growing by the 

 everlasting deposit of meteoric debris. Looking back 

 through the vistas of time past;- it becomes impossible to 

 estimate how much of the solid earth may not owe its 

 origin to this celestial source. ^ J 



It will greatly promote our comprehension of these 

 bodies if we group them into classes so as to discover 

 some of the laws by which their movements are guided. 



