RicHarpson—Lines of Flow of Water in Saturated Soils. 297 
The tube was now filled with filtered water and set upright ; and 
the rate of depression of the water-level was observed. The total 
difference of pressure tending to drive water through the plug is 
proportional to the height of the water-surface above some level 
in the plug. Just where this level comes in the plug depends on 
the proportion of water and solid therein. Ata guess I took it 
as the section AB in the figure (fig. 2). Then calling z the height 
of the water-surface above AB, the pressure-difference is gpg, 
where g is acceleration of gravity, and p the density of water. 
The mass-acceleration is found to be entirely negligible. 
glass 
Fie. 2. 
ao a) GE zi P , 
The flux is 7 oc: PEF Sq. om. per second. So that, if the flux is 
proportional to the pressure-difference, we have = =-—kz, where 
k is a positive constant, namely, the conductance of tube 1 sq. em. 
area cut longways from the plug. Integrating = de“. If in 
the observations 2, corresponds to 4, and s, to tf, then by dividing 
we have 
whence 
2R 2 
