278 Application of Barometer for indicating the Weather 9 



4thly Seek in the column of temperatures, Table I., for 

 the temperature observed at the stations, (or for the mean 

 of the two, if they differ,) and note down the number of 

 feet, tenths, and hundredths, which are placed opposite to 

 that temperature in the adjoining column. 



5thly. Make corrections (if requisite) from Table II. 



6thly. Multiply the numbers, so found and corrected, 

 by the difference between the altitudes of the barometer at 

 the lower and upper stations. 



7thlv. Add to the product the increased ratio, from 

 Table III., which finishes the process. 



Table I exhibits the number of feet, tenths, and hun- 

 dredths, in perpendicular altitude, indicated by the descent 

 of the mercury in the barometer for each hundredth part 

 of an inch; which descent varies according to the tem- 

 perature of the air, at the rate shown in the corresponding 

 column. This table is constructed on the supposition that 

 the barometer at the lower station is at 30 inches. 



N. B. Although this calculation be given for each hun- 

 dredth part of an inch of variation on the barometer, it may 

 be used for variations of one tenth, or of one inch, by merely 

 altering the denomination of the figures in the column, thus : 



Feet. Tenth Hund. 



The variation of 100th part of an inch, at temO . 



perature 90°, indicates altitude of r' ' 



Feet. Tenth. 



The variation of a 10th part of an inch 99 > 5. 



Feet. 



The variation of an inch 995. 



Table II. shows the alteration which must be made in 

 the numbers taken from Table I., when the barometer is 

 not at 30 inches in the lower station. If it be lower than 

 30 inches, the number of feet, which are placed opposite to 

 the barometer's height in this table, must be added to the 

 feet r& altitude corresponding with the descent of the mer- 

 cury in the barometer for one inch. If it be higher than 30 

 inches, subtract instead of adding. 



N. B. It the variation of the barometer be not so much 

 as an inch, but only some tenths of an inch, then the 

 figures in the second column will not represent feet, but 

 tenths of feet to be added or subtracted. 



Table III. shows the number of feet to be ultimately 

 added to each 100 feet of altitude. This number varies 

 from 1 to 46 > according as the barometer in the upper sta- 

 tion stands between the altitudes of 31 and 14 inches. 



N. B. A table for the correction, or equation of heat,, in 

 the barometer, when the temperature of the atmosphere 

 differs at the upper and lower stations, is provided for here, 

 by the adjustment of the table of temperatures. T\ble 



