A writer who goes by the name Calliban has posted about the Trompe Hydraulic Air Compressor.
A recent post is about wave power, as a related concept: http://newmars.com/forums/viewtopic.php ... 31#p214431
A quick search for posts about Trompe include:
http://newmars.com/forums/viewtopic.php ... 23#p214323 Ragged Chute air plant in Ontario
http://newmars.com/forums/viewtopic.php ... 10#p206810 Explanation of operation
http://newmars.com/forums/viewtopic.php ... 93#p206793 Explanation of operation
http://newmars.com/forums/viewtopic.php ... 78#p206778 Wikipedia article and discussion
http://newmars.com/forums/viewtopic.php ... 31#p162831 Discussion
http://newmars.com/forums/viewtopic.php ... 38#p162638 Original post explaining air bubbles compressed by water