The Cities in Flight series by James Blish. Great stuff, Peace! I read the series as separate novels back in the Sixties. I think I have them around here somewhere and they definitely merit re-reading. Mind-boggling! Thanks for the reminder!

I saw a science program on the tube a few of weeks ago where a couple of heavy-duty physicist were discussing possible space drives. One of the things they talked about was using a rapidly rotating mass to control gravity waves. Sounds a bit like Blish's "spindizzy" antigravity device.

Don Firth