Histonj of AstroiwmiJ for the Year 1S06. 77 



was brother to our celebrated geographer, and I had pro- 

 cured him the means of going to exercise his zeal ia a 

 country ahnost unknown, where important observations 

 might be made: to him only we are indebted for any know- 

 ledge of the marshes of Cayenne. 



The class of Sciences having resolved to publish their 

 memoirs half-yearly, were only able to publish tht;ir vo- 

 lume for the first half of 1806 on the 8th of December. 

 It contains memoirs by M. Legcndre upon triangles, in the 

 spheroids; by M. Burckhardt upon the comets of 1703, 

 1770, and 1784, and upon Harding's planet; and some ex- 

 periments of Messrs. Biot and Arrago upon the refractive 

 power of the different gases, a very interesting object to 

 astronomical refraction. The class of Sciences offers a con- 

 siderable -prize for an account of the perturbations of 01- 

 bers's planet. 



M. Delambre has observed the equinoxes and the sol- 

 stices, and has found no cause for changing his new 

 tables. 



M. Piazzi has examined the question on the obliquity of 

 the ecliptic, which has been a long lime in dispute. The 

 winter and summer solstices of 1604 have given him 7" less 

 in winter than in summer: he does not think that this can 

 arise from the variations in refraction : he was led to ascribe 

 it to the light of the sun being more refiangible than that of 

 the stars, whence it would follow that the refractions de- 

 duced almost singly from the stars would not agree with the 

 sun: he thinks he is certain, from his own observations, that 

 the refractions of the stars are the same night and day. He 

 thinks ihat from the zenith to the winter solstice the re- 

 fractions can only be two seconds in error : this is not suf- 

 ficient to explain the differences from l" to 8" found be- 

 tween the two solstices by the observations of ]\1e«srs. Pi- 

 azzi and those of Greenwich. M. Delambre only finds 4" 

 as well as M. Chiminello. M. Piazzi thinks that a new 

 element must enter into the calculations of refractions, ex- 

 pecting further light upon the subject: he thinks that the 

 obliquity cannot be deduced except from the ob.^ervations of 



sumiwcr. 



