"John and I have provided for that, while Bob is responsible for the electrical features I have just mentioned," said Paul.  "You will notice that at the top of the mercury channel there is a dividing wall. A tube runs from the left side of this wall to the right wing of the airplane, also from the right side of the wall to the left wing.  At the end of each tube there is what we call a 'venturi tube.'  This is a kind of suction device operated by the wind.  The wind which blows through the left venturi tube sucks the air out of the right-hand side of the mercury tube, and the right venturi tube sucks the air out of the left-hand side of the mercury tube.  The stronger the wind, the greater the suction.  Now, when making a turn to the right the left wing must travel faster than the right wing, and so there must be more suction in the left venturi.  This produces a greater suction in the right-hand side of the mercury tube, which draws the mercury up on that side and down on the other, until the proper electrical contact is broken and the ailerons are returned to neutral position."