THE U-TUBE LEVEL

This simple builder's level of recent times works on the principle of the U-tube in which water finds its own level. A long flexible tube of rubber or polythene is laid along the ground. One end is held vertical against the mark from which the level is to be taken, the other end is also held vertical, but initially rather higher, at the point to which the level is to be transferred. The tube is then filled until the water reaches the brim at the starting end, and the other end is slowly lowered until it coincides with the water surface. Because no sighting is involved, the result is extremely accurate. The question of whether the method was used in the ancient world has in the past been asked, but rejected on the grounds that making a U-tube of sufficient length would have been difficult.

Flexible pipes, however, were not unknown. A leather pipe at least 50 cubits long, no doubt sewn and greased, was used to raise fresh water to the surface from a spring on the sea bed off the Phoenician coast, and others for carrying steam were installed in a fiendish early Byzantine device. A better material, because less prone to leakage and easier to make, would be animal intestine.