Astronomical and Nautical Collections. 431 



The opposition to the sun will be 1828, Oct. 12.34; while its 

 light is weak, it may be observed on or near the meridian. 



On the 10th of Nov. 1828, its distance from the sun will be the 

 same as at the time of its discovery in 1818, and it will be consider- 

 ably nearer to the earth ; and on the 21st of December, its position 

 with respect to the sun will be the same as at its last observation 

 in 1819 ; and with respect to the earth, its situation will be more 

 advantageous. The 1st of January, 1829, it will set with the sun. 



It follows, that the most advantageous time for seeing it will be 

 during the whole of November, and the first 25 days of December. 

 It will scarcely be seen before the end of September, as it has here- 

 tofore never been observed more than two months before the time of 

 its perihelion, and even in the dark winter nights will scarcely be 

 visible more than 14 or 15 weeks before that period. After the peri- 

 helioii it will not be visible in these parts of the world. 



ii. Elementary F/^?^) o/^A^ Undulatory Theory of Light. 

 By Mr. Fresnel. 



[Continued from the last Number.] 

 In order to complete the explanation of the conditions neces- 

 sary for the formation of the fringes, it remains to show why 

 a small hnninous point must be employed in experiments on 

 diffraction, and not an object of any considerable dimensions. 

 If we resume the case of the interior fringes of the shadow of 



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