> Thanks Uli. I encountered these tyemperature-controlled devices as a > youngster about 70 years ago, but did not know that they were hydraulic. > Are they still being made? Energy-saving, I'd think and need to be brought > back or re-popularized for today's world These are available in almost any Garden Centre, or from a greenhouse supplier, in the UK. Just Google "automatic window opener". Different lifting strengths available. Some get tired after about 20-30 years or so, and stop working. I guess they leak slowly. Brian Whyer, Buckinghamshire, England, zone ~8