French National Institute. J3 



in preference the result of these physical experiments; it i.i 

 only by calculating with the greatest precision, millions of 

 observations made at different times, and with different 

 kinds of nistmnients, that we can attain this puinl of ap- 

 proximation. If we afterwards compare thfe new table of 

 refractions with those of Bradley, Mayer, Burg, and Piazzi, 

 we shall per'n^ps be astonished at the little that has Leea 

 gained by so many various observations, calculations, and 

 experiments: but such is the present state of astronomy, that 

 the greatest efforts can produce little more than aliiiost in- 

 sensible ameliorations, although we certainly gain in point 

 of accuracy in proportion as experiments become more exitct 

 and rigorous. The same comparison will prove that the 

 greatest difference. between the various, tables chiefly belongs 

 to the constant factor of the Ihermometrical correction. In 

 fact, as far as 80° of distance from the zenith, at which the 

 observations differ more from each other than they are re- 

 moved from the tables, scarcely can we find, in the mean 

 refractions, one or two seconds of difference among astro- 

 nomers, if we except M. Burg, who has frequently a double 

 quantity in excess, instead of our seeing in very high or very 

 low temperatures uncertainties of 9 or 10 seconds. It was 

 therefore extremely necessary to verify this co-eHicient; and 

 this is what M. Biot has done with the same success. The 

 quantity which he found, according to his own experiments 

 and those of Gay Lussac, scarcely exceeds what JVJayer liad 

 determined 50 years ago, and to which Lacaiile found al- 

 most nothing to add. Bradley made this co-eilicient a little 

 larger, and almost every astronomer has adopted his table. 



M. Biot, who employs his time so usefully, ai^o read se- 

 veral excellent memoirs to the Institute this year ; but his 

 departure for Spain does not admit of our analysing them: 

 he is at present occupied at Formentera, a small island tQ 

 the southward of Ivica, in measuring the aititude of the 

 pole, the length of the pendulum, and the azimuths of the 

 most southern points of the triangles which he drew from 

 that island to Tortosa, where the death of M. Mt-chain liad 

 caused them to be suspended. Messrs, Cli lix and Rodri- 

 guez, bi^t above all M. Ar^igo, took the most active part in 



this 



