1818.] Royal Academy of Sciences. 141 



March 30. — M. de Varennes delivered in a description of a 

 species of incombustible cloth, which was referred to a com- 

 mittee. 



M. Desfontaines made a report on M. Dellile's memoir on the 

 Persea. 



The persea was a tree formerly cultivated in Egypt for the 

 sake of its fruit, and of which Theophrastus, Dioscorides, Pliny, 

 and other ancient naturalists have made mention. The former 

 of these writers thus describes it. " There grows in Egypt a 

 remarkable tree called persea. In its leaves, flowers, and man- 

 ner of growth, it resembles the pear tree ; but differs from it 

 in being evergreen. It produces fruit in abundance, which 

 ripens about the time of the Etesian winds. When the fruit is 

 intended to be kept, it is gathered before it is quite ripe. In 

 this state it is of a greenish colour, and in form like an almond 

 or elongated pear : the pulp, which is soft, agreeable to the taste, 

 and of easy digestion, incloses a stone like that of a plum, but 

 smaller and harder. The wood of the persea is dense, and of a 

 fine black colour, and is used for making tables and statues." 

 Many modern naturalists have sought for this tree, but without 

 success. M. de Sacy, in his translation of the Description of 

 Egypt, by Abdallatif, an Arabian physician, proves that the 

 tree described by the ancient writers of that nation under the 

 name of lebakh, is the persea of Theophrastus- This tree has 1 

 for some ages past disappeared from lower Egypt ; but M. Dellile 

 thinks that he has recognized it in the Xymenia Egyptiaca of 

 Linnaeus, of which he saw one specimen in a garden at Cairo, 

 and two others in Upper Egypt. It is, however, common in 

 Nubia and Abyssinia, where it is known by the name of glig- 

 The committee think the opinion of M. Dellile to be in all pro- 

 bability well founded, and propose that his memoir should be 

 inserted among the Scavans etrangers. 



M. Poisson read a memoir on the Motion of Elastic Fluids. 



The reading of M. Beudant's memoir was concluded, and was 

 referred to a committee. 



M. Fresnel read a memoir on the Colours produced in homo- 

 geneous Fluids by polarized Light. 



M. Moreau de Jonnes read a memoir on the Coluber Cursor of 

 Martinique. 



April 6. — M. Dupin presented in manuscript that part of his 

 Voyage en. Angleterre relating to the construction of ships ; it 

 was referred to a committee. 



M. de Lavalette gave in a supplementary letter on the 

 musical notation of the Greeks ; this also was referred to a 

 committee. r 



M. Biot presented a specimen of the glass employed by Mr. 

 Stevenson in the Bell-rock light-house in Scotland. It is a red 

 glass, the colour of which is occasioned by a thin, superficial 

 coating of metallic oxide. The cost is considerable ; and the 

 reporter suggests that hollow glasses of any desired form, and 



