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Examples, 



Barometer being at 30 inches, what is the length of a 

 vertical column of air that weighs, as much as the tenth of a cubic 

 inch of mercury ? 



Here 29,9 is the number which is ~ lower than 30. Then 

 log. 30 — log. 29,9 gives the length required, in fathoms and. 

 parts of fathoms. Log. 30 = 477 121 



Log. 29,9=475671 



Then the length required is - 14,50 fathoms.- 



Here 14, is the difference of the four firft figures of the 

 logarithm, and 50, that of the two laft figures, and therefore deci- 

 mal parts. 



Note. — When the barometrical height or heights are marked' 

 by mixed numbers, their logarithms muft be fought as if they 

 were integral numbers, and if one of them be an integer, it muft 

 be raifedr by. the addition of a cypher or cyphers to the fame 

 number of places. aS' the other has. 



Thus in the above example 29,9 is confidered as 2199, and.1 

 30 as 300. 



Seconds 



