ins TORT of the SOCIEtr, 25 



have the obfervations repeated at difFerent feafons of the year* 

 An obferver equally affiduous with Dr Baj^four will not be 

 eafily found ; but it will perhaps be fufficient to obferve the 

 barometer every three hours, and particularly at the ftationary 

 points. 



It is proper to remark here, that fome obfervations t)f a limi- 

 lar fort have been made in Europe; where, though the fituation 

 is far lefs favourable, than in India, for difcovering the true 

 law of fuch minute variations, refults have been obtained tole- 

 rably confident with one another, yet differing confiderably 

 from thofe that are dated above. 



A SERIES of fuch obfervations was inftituted by M. Planer 

 of Erfort in Germany, and is defcribed in the Ephemerides of 

 the Meteorological Society at Manheim for 1783. Before thefe 

 obfervations, it had been remarked, that when the barometer is 

 riiing, it ftands lower at noon than at any other time of the 

 day, and higher at the fame hour when it is defcending. M, 

 Planer's obfervations feem to extend and modify this conclu- 

 fion ; for they make it appear, that between ten and two, both of 

 the day and night, that is, for two hours before, and two hours 

 after the fun is on the meridian, the elevations and dcpreffions^ 

 of the mercury are lefs than at any other time of the day ; and 

 that between fix and ten in the morning, and, again, between 

 fix and ten at night, thefe elevations and deprefiions are the 

 gr^ateft. The fame rule feems to be confirmed by the obferva- 

 tions of M. CoTTE. in France, of which he has given an account 

 in the Journal de Phyfique for 1792 and 1794. 



These laft conclufions leem to indicate fome periodical re- 

 tardation of tlie movement of the mercury in the barometer, 

 whethei; afcending or defcending; but it is difficult to form any 

 notion of the force by which fueh an effedt can be produced. 

 Perhaps the only general inference that is yet deducible, fronat 

 comparing all the circumftances, is, that certain diurnal va- 

 VoL. IV. d riations 



