THIRD PERIOD. 127 



casions is open only to the pupils, who are at 

 liberty to continue their work on the interven- 

 ing days, and are often assisted with the advice 

 of the professor. 



As it is necessary to adapt the instructions to 

 the greater number of pupils, the professors 

 cannot in their courses enter into minute details, 

 nor expose discoveries and principles which 

 would be understood only by men versed in 

 science ; for these objects the Annals of the Mu- 

 seum offer an appropriate medium of communi- 

 cation. In this work M. Haiiy has fixed the cha- 

 racters of different minerals recently added to 

 his cabinet, and shewn the simplicity of the laws 

 of crystallography, and the advantage of analytic 

 formulas ; MM. Fourcroy, Yauquelin and Laugier 

 have communicated the most important results 

 of their experiments in the chemical laboratory ; 

 M. Desfontaines has described new genera of 

 plants, that have bloomed in the garden or been 

 found in the herbarium ; M. de Jussieu has defined 

 the characters of the principal natural families, 

 with such additions and correc tions as the progress 

 of the science has necessitated in his work; 

 M. Thouin has explained in detail the management 

 of the seed-beds and plantations, and the processes 

 of grafting ; MM. Geoffroy and Lacepede have 

 published new genera of quadrupeds, bats, rep- 



