Intelligence and Miscellaneous Articles, 



235 



to find it collected in cosmical clouds similar to the visible nebulae. 

 Now this, in fact, is precisely what has been observed in regard both 

 to comets and meteors. In 150 years, from 1600 to 1750, sixteen 

 comets were visible to the naked eye*, of which eight appeared in the 

 twenty-five years, from 1664 to 1689. Again, during sixty years, from 

 1750 to 1810, only five comets were visible to the naked eye, while in 

 the next fifty years there were double that number. The probable 

 cause of such variations is sufficiently obvious. As the sun in his 

 progressive motion approaches a cometary group, the latter must, by 

 reason of his attraction, move toward the centre of our system, the 

 nearer members with greater velocity than the more remote. Those 

 of the same cluster would enter the solar domain at periods not very 

 distant from each other — the forms of their orbits depending upon 

 their original relative positions with reference to the sun's course, 

 and also on planetary perturbation. It is evident also that the pas- 

 sage of the solar system through a region of space comparatively 

 destitute of cometic clusters would be indicated by a corresponding 

 paucity of comets. By the examination, moreover, of any complete 

 Table of falling stars, we shall find a still more marked variation in 

 the frequency of meteoric showers. 



Previously to 1833, the periodicity of shooting-stars had not been 

 suspected. Hence the showers seen up to that date were observed 

 accidentally . Since the great display of that year, however, they 

 have been regularly looked for, especially at the November and 

 August epochs. Consequently the numbers recently observed can- 

 not properly be compared with those of former periods. Now, accord- 

 ing to the Catalogue of Quetelet, 244 meteoric showers were observed 

 from the Christian era to 1 833. These were distributed as follows: — 



Centuries. 



i 

 Number of 

 showers. 



Centuries. 



Number of 

 showers. 







Oto 100 



5 



1000 to 1100 



22 



100 to 200 







1100 to 1200 



12 



200 to 300 



3 



1200 to 1300 



3 



300 to 400 



1 



1300 to 1400 



4 



400 to 500 



1 



1400 to 1500 



4 



500 to 600 



20 



1500 to 1600 



7 



600 to 700 



1 



1600 to 1700 



7 



700 to 800 



14 



1700 to 1800 



24 



800 to 900 



37 



1800 to 1833 



48 



900 to 1000 



31 



j 





A remarkable secular variation in the number of showers is ob- 

 vious from the foregoing Table. During the five centuries from 

 700 to 1200, 116 displays are recorded; while in the five succeed- 

 ing, from 1200 to 1700, the number is only 25. It will also be ob- 

 served that another period of abundance commenced with the eigh- 

 teenth century. A catalogue of meteoric stonefalls indicates also a 



* See Humboldt's * Cosmos,' vol. iv. p. 538. 

 tion to this variation as long since as 1861. 



The writer called atten- 



