[ r^: ■.] 



To ufe this table, wite ont the decimals corre)(ponding to the 

 given heif^ht of the haroruster in inches and decimal parts, 

 lowerm-f the places of the decimals for the pdd inches and tenths 

 above or Vjclow 30 inches. Add all together, and muhiply the 

 fum by the difference in degrees of the attached thermometer 

 from 55*. This produifb applied to the obfcrved height — or+as 

 the temperature of the barometer was above or below 55°, will 

 give the corred height for the mean temperature. Note, this 

 corredion is to be regulated by the attached thermometer at 

 every ftation and obfervation ; and is intended with a view to 

 afcertain and allow for the adtual temperature of the mercury in 

 the feveral barometers. 



As the expanfive power of heat and the contradion of cold do 

 alfo fo affe£t the atmofphere, that as thefe caufes vary a longer 

 or fhortcr column of the atmofphere, and of courfe different 

 intervals of height, will be indicated at different times by a column 

 of mercury of the fame length, and reduced as above to a ftandard 

 temperature. 



It therefore becomes neceffary to corredt the differences of 

 heights {hewn by the reduced columns of mercury at the different 

 ftations, by a calculation founded on the effeds of heat and cold 

 on the atmofphere. The argument for this calculation is the mean 

 temperature of the atmofphere, obtained by adding together the 

 heights of the mercury in the detached thermometers at the dif- 

 ferent ftations, and dividing the fum by 2. This mean may be 

 called an imaginary temperature. 



TABLE 



