4 HIStORT of the SOCIErr. 



The firft of the obfervations here referred to were made by 

 M. Lamanon, an ingenious natura'.ifl: who accompanied Pey- 

 ROUSE, and who has given an account of them, (fee 4th vo- 

 lume of the Voyage, 8vo edit,), in a letter to M. de Condorcet, 

 dated, St Catherine, 5th November 1785. Dr Balfour's Ob- 

 fervations are in the Afuitlc Refearches for 1744, and a fliort ac- 

 count of them is aUb infcrted in the 4th volume of the T'raiifac- 

 tiotis, R. S. Edin. Hift. p. 23. 



M. Laivi ANO'^'s'obfervations were made in confequence of 

 inftruiftions from the Academy of Sciences, directing him to keep 

 an exadt account of the heights of the barometer in the vicinity 

 of the equator at different hours of the day, with a view to dif- 

 cover, if poffible, the quantity of the variation of that inrtru- 

 ment, due to the adlion of the fun and moon, that quantity 

 being there probably at its ;;/(7.v/ot//;;/, while the variations arifing 

 from other caufes are at their min'nnum. 



M. Lamanon was provided with one of Nairne's marine ba- 

 rometers, which, he fays, was fo little affedled by the motion of 

 the fliip, that it might be depended on to the -^^ of an inch. 

 In this barometer, he tells us, that from about the i ith degree 

 of north latitude, he began to perceive a certain regular motion, 

 fo that the .mercury ftood higheft about the middle of the day, 

 from which time it defcended till the evening, and rofe again 

 during the night. As they approached the equator, this became 

 more diftindtly perceptible ; and on the 28th of September, the 

 ihip being then in \° 17' north latitude, a feries of obfervations 

 was begun, and continued, for ev^ry hour till the ifl of O'dober, 

 at 6 A. M. The following abftraiSl fhews the refult of the ob- 

 fervations on the 2Sth and 29th. 



Cprom 4 to 10 A. M. Barometer rofe i /. t'o 



28th Sept. ^From 10 A. M. to 4 P. M. . fell i r% 



(^From 4 to 10 P. M. rofe o VW 



29th 



