Hele-Shaw & Hay. 
Phil. Trans., A., Vol. 195, Plate 16 . 
Double Cylindric Shield of very low 
permeability. 
Double Cylindric Shield enclosing Solid 
Cylinder. Permeability = 100. 
Triple Circular Cylindric Shield. 
Theoretical Diagram. 
Permeability=100. 
Triple Circular Cylindric Shield. 
Stream-line Diagram. 
Permeability = 100. 
