146 



BOOK V. 



as in the case of the suspended plummet level, but is fixed to the instrument in 

 a half-lying position. They measure the tunnels for the purpose of knowing 

 how many fathoms they have been increased in elevation ; how many fathoms 

 the lower is distant from the upper one ; how many fathoms of interval is 



Indicator of a suspended plummet level. 



