56 BAROMETRICAL CHAKGESa 



XIII, 



.;hj/'.- "(' ^ Compar/fon of fome Objervalions on the Diurnal Variations of 

 the Barometer^ made in Peyroufc's Voyage round the Worlc^t 

 xvi(h thofe made at Calcutta by Dr. Balfour *, 



Barometrical JL HE firft of the obfervalions here referred to were made by 



two»n*the"* '* ^^' Lamanon, an ingenious naturalift who accompanied Pey- 



Tropicsby roufe, and who has given an account of them, (fee fourth 



^™^'jj^^^°'^''y volume of the Voyage, o6tavo edit.), in a letter to M. de 



Condorcet, dated St. Catharine, 5th November 1785. Dr^ 



Balfour's Obfervations are in the Afiatic Rtfearches for ITQ*, 



and a fliort account of them is alfo infcrted in the fourth 



volume of the TranfaSiions, R. S. Edin. Hift. p. 2.3. 



M. Lamanon's obfervations were made in confequencc of 

 inftrudtions from the Academy of Sciences, direcling him to 

 keep an e^^aft account of the heights of the barometer in the 

 vicinity of the equator at different hours of the day, with a 

 view to difcover, ifpoflible, the quantity of the variation of 

 that inf?rament, due to the a^ion of the fun' and moon, that 

 quantity being there probably as its maxivmin, while the varia^* 

 tions ariHng from other caufes are at their minijuum. 

 Lamanonufed a M. Lamanon was provided with one of Nairne's marine 



marine Baro- barometers, which, he fays, was fo little affecled by the 

 oicwr u* Nairne. • -^ ' J 



motion of the ftiip, that it might be depended on to the -j-©^ 

 of an inch. In this barometer, he tells us, that from about the 

 1 1th uegree of north latitude, he began to perceive a certain 

 regular motion, fo that the meixrury flood higheft about the 

 Regular diurnal middle of the day, from vvhich time it defcended till the 

 S^lhTn'""^" evening, and rofe again during the night. As they ap- 

 u«. N. proached the equator, this became more diftinflly perceptive; 



and on the 28lh of September, the Ihip being then 1« 17' 

 north latitude, a feries of obfervations was begun, and con- 

 tinued for every hour till the 1ft of Odlober, at 6 A. M. 

 The following abftrad (hews the refultof the obferva^tioais oq 

 the 28th and 29lh. 



T'werUy eighth of September. 

 From 4 to 10 A. M. Barometer rofe U. -^^ 



From 10 A. M. to 4 P. M, fell \ ^\ 



From 4. to 10 p. M. yofe -,% 



"^ from the Hiftory of the Royal Society of Edinburgh, 1805, 



