755 



for Paris, scarcely 0.78 mm ; for la Chapelle *, 

 near Dieppe, 0.36 mm . I know of no precise or 

 numerous observations for the latitude of 60° ; 

 but M. Bessel has published a very important 

 result which corresponds to the parallel of 

 Koenigsberg (lat 54° 42'), where the mean of 

 eight years of observations made by M. Sommer 

 with the same instrument, and reduced to the 

 temperature of 10° cent, gives, for 8 h and 9 h in 

 the morning, 337.35 l H ; for 2 h and 3 h in the 

 afternoon, 337.264 11 ; and for 9 h and 10 h in the 

 evening, 337.35 V\ The extent of the horary 

 oscillations is therefore at that high latitude, 

 only 0.087 11 (scarcely the one-tenth of a milli- 

 meter), or 4 times less than at Paris. M. Bessel 

 adds, that those observations at Kcenigsberg 

 are so precise, that, notwithstanding the s m ali- 

 nes s of the oscillations, the value of the horary 

 variation is ascertained in the mean of each 

 year-f-. 



The mean height of the hour of noon at 

 Paris, scarcely differs in a whole year, accord- 

 ing to the remark of M. AragoJ one-tenth 



* Mean of four years (from 1819 to 1822). The small- 

 ness of the oscillations perhaps depends, according to M. 

 Arago, on the elevation of the spot, which is not a table- 

 land. M. Nell de Breaute, in the BibL univ., Tom. xxii, 

 p. 105. 



f Schumacher, Astron. Nichrichten, 1823, p. 26. 

 X Annales de Chimie, Tom. ix, p. 428. M. Billiet finds 

 that at no season, at Chambery, the mean of noon differs § 



3 d 2 



