E. W. Evans on the Action of Oil-Wells. 165 
Examples differing in details might be multiplied indefinitely. 
I have aimed only to point out in a general manner the different 
modes of action, and the hypotheses on which they are to be 
explained. 
n the foregoing illustrations the quantity of gas has been sup- 
posed considerable. In many cases however it is so slight 
that the pump has to be used throughout. Yet wells of this 
kind often partake of the intermittent character to some extent. 
Consequent cessation of flow whenever the oil is red toa 
certain level, If collections of oil had direct and free connection 
