16 M. Arago on the Number of' 



years, if every three years were to supply four comets, as has 

 just been said, the 300 years would furnish 400 comets. Such, 

 then, according to this mode of reasoning, would be the number 

 of the comets of the solar system, which would be visible from 

 the earth. 



But I shall not stop now to canvass these calculations, that 

 I may immediately address myself to considerations of a much 

 more elevated character, by the help of which Lambert had pre- 

 viously endeavoured, in his ingenious Lettres Cosmologiques, to 

 arrive at a solution of the curious problem which forms the sub- 

 ject of this chapter. 



On the 31st December 1831, the number of comets whose 

 orbits could be accurately calculated was 137. Let us now exa- 

 mine if, in their movements, these luminaries shew a tendency 

 for any peculiar epochs, or any especial directions. 



Epochs of their Passing the Perihelion. — In January there 

 pass 14 comets, February 10, March 8, April 10, May 9, June 

 11, July 10, August 8, September 15, October 11, November 

 18, December 13 ; total 137. 



There are evidently fewer comets in the summer than in the 

 winter months ; and it could scarcely be otherwise, on account 

 of the shortness of the nights during the months of May, June, 

 July, and August. The long duration of the day properly so 

 called, and also the brightness of the twilight, cannot fail to hide 

 from our view a certain number of these bodies. 



Direction of their Movements. — Number of direct comets, 69 ; 

 number of retrograde, 68 ; total 137. 



If this comparison had been made when the number of comets 

 whose orbits were accurately calculated was only 49, there would 

 then have been 24 direct, and 25 retrograde, in their move- 

 ments. 



Inclinations of their Orbits. — From 0° to 10°, the number of 

 comets is 9; 10° to 20°, 13; 20° to 30°, 10; 30° to 40°, 17; 

 40° to 50°, 14 ; 50° to 60% 23 ; 60° to 70°, 17 ; 70° to 80°, 19 ; 

 80° to 90°, 15; total 137. 



It seems to follow from this table, that the comets are more 

 common in the greater inclinations than in the smaller. Bode 

 had come to the same result, from considering the elements of 

 72 comets which were known in 1785. At the same time, we 

 have only to glance at the catalogue of this astronomer, to per- 



