[ '°8 ] 



necefTary to complete the obfervcrs, they fhould unqueftionably 

 be made by feparatc obfervations at the fame inftant of time, to 

 be afcertained cither by fignals or by a previous comparifo« and 

 adjuftment of their feveral time-keepers. 



The Things to be done are, 



I ft, To obferve accurately the heights of the mercury in the 

 barometer at the refpedlive places of obfervation, and carefully to 

 note the differences. 



2d, To obferve the temperature of the mercury in the barometer, 

 by confulting the attached thermometer of each barometer at the 

 different places of obfervation. 



3d, To note the temperature of the air, by obfeVving alfo at 

 each ftation the ftate of the detached thermometer in the fhade. 



These obfervations being carefully made, and the neceffary 

 allowances and calculations gone through, the refult will give 

 very corredly the difference of the adual height of the two 

 Jiations. 



T$ 



