There's been that much going on I forgot that one, sorry Nigel. So we have two ideas to eliminate slippage, so much the better. I've been thinking about Steves rotating pivot log and how to secure it to the stone. So here goes, use a fairly substantial pivet log, place a similar log on top of the stone directly above the first, join the two together with logs each side of the stone using motise and tenon joints with an extended tenon. (like the legs of a refectory table) When the wedges are driven home it will grip the stone like a vice. If that's still not enough do the same again further down the stone (about three foot) and join the two rings together with cross bracing. That should hold forty ton for the time period required.

> So what's wrong with something along my previous idea, tying some logs along the stone and notching them? The notches would effectively hook onto the corner of the tower and the whole thing would pivot round until it fell cleanly.

I like the principle, but the problem is how to fasten the logs to the stone. When the stone reaches the angle at which it would have slipped, it is going to try to slip along the logs. The only thing restraining it is friction. For the block not to slip along the logs the rope has to increase the contact force with the logs to a point that does no exceed limiting friction. For a coefficient of friction of 1 the binding would have to produce 40 tons of pressure between the block and its logs in order to support it at the vertical. I know we dont't need to go that far, but the coefficient is probably less than 1 and we may need to get to 80 degrees or so. Of course 40 turns of rope around the block would mean that the average strain on the rope would only be 1 ton. Do we know what kind of ropes were available at the time and how thick a 1 ton rope of that era would be?

Actually the same argument applies to Gordon's suggestion of using wedged mortice and tenons. Would they be strong enough to increase the frictional force sufficiently?