VOL. XXXVIir.] PHILOSOPHICAL TRANSACTIONS. 637 



Fig. 6, tlie fruit cut into two halfs, containing 6 segments : n tlie segments 

 good to eat, of unequal sizes ; o the calix ; p the pedicle. 



Fig. 7, a separate segment of the fruit, in the shape of a half-moon, con- 

 taining a grain. 



Fig. 8, a grain or seed separated from the segment, its coat covered with 

 filaments, which formed the parenchyma of the segment. 



Fig. Q, a leaf of the tree which bears the mangostans, with its fellow cut off 

 near the bottom, supported by a piece of its twig. 



y^n Account by Mr. John Eames, F. R.S. of a Booh entitled, Traite Physique et 

 Historique De V Aurore Boreale,Par Mr. De Mairan.* Suite des Memoires 

 de rAcademie Roy ale des Sciences, Annee 1731: or, a Philosophical and 

 Historical Treatise concerning the Aurora Borealis. By Mr. De Mairan, 

 being a Supplement to the Memoires of the Academy of Sciences for the Year 

 1731. N°431, p. 243. 



The frequent appearances of the northern lights in several parts of Europe 

 and America, and the surprising beautiful phsenomena that have been observed 

 in some of them, such as the rainbow-colours, canopy, &c. have very justly 

 engaged the philosophers of the present age in a search after their causes ; and 

 several hypotheses have been invented and proposed by the learned, to explain 

 them. Most of them suppose these phosphorus like appearances to proceed from 

 certain effluvia, either perspired out of the earth, or at least passing through it. 

 But our ingenious author has thought of a cause very distant, as well as very 

 different from all these, viz. the atmosphere of the sun, which at some times 

 shows itself under the appearance of a light, which he calls the zodiacal light, 

 but at other times produces an aurora borealis. The zodiacal light is the purer 

 unmixed atmosphere of the sun ; but an aurora borealis is the effect of the 

 solar atmosphere, consequent on its making a descent into, and blending itself 

 with the atmosphere of the earth, at certain times and seasons of the year. 



The work consists of 5 sections ; the first gives a short history of the 

 zodiacal light. In the 2d he treats at large of the atmosphere of the earth ; its 

 altitude, and the height of the aurora borealis in it, and the exclusion this cir- 

 cumstance gives to some of the causes, which have been already assigned, of 

 this phenomenon. In the 3d he proposes the cause, and accounts for the for- 

 mation of this appearance in general, and then descends to a detail of the 

 several particulars, adding the solution of each. The next section is employed 



• M. de Mairan was author of various philosophical treatises, viz. Dissert, de la Glace; Dissert, 

 sur les Phosphores ; Traite de 1' Aurore boreale, &c. He succeeded Fontenelle in the office of secre- 

 tary to the Parisian Acad, of Sciences, and wrote a vol. of Eloges of deceased members. A number 

 of communications of his are inserted in the Memoirs of the aforesaid Academy. He died in 1771, 

 aged 93. 



