The futile attempts to patch up S. Paul's were in 1673 at last abandoned, and Wren ordered the ground to be cleared that new foundations might be laid. A great mass of material for building had had to be disposed of while the repairs were going on. The Archbishop of Canterbury, the Bishops of London, Winchester, and Oxford, and the Lord Mayor, were commissioners for the repair of S. Paul's; from them Wren obtained an order that-- 'The clerk of the works shall be required to dispose of and sell the stone, chalk, timber and free stone for, and towards, the rebuilding of the parochial churches and to _no other use whatsoever_, as he shall be directed, at merchantable rates to the masons and carpenters that build the said churches by order of Sir Leoline Jenkins (judge of the Admiralty Court), Dr. Sancroft, and Dr. Wren, or any two of them.' The money thus collected was put aside for the fabric of the Cathedral. [_USE OF GUNPOWDER._] Though much of the old material was removed in this manner, and yet not diverted from its proper purpose, the ground was by no means clear. Wren, appointed under the Great Seal, architect of S. Paul's, and one of the commissioners in the new commission for its rebuilding, had to take down by degrees what portions of the old building were still standing. Warped and cracked as they were, the walls, eighty feet high and five thick, were yet strong enough to make the process of pulling down both difficult and tedious. Wren determined to avail himself of the knowledge he had acquired in the Royal Society's recent experiments in raising weights by means of gunpowder. Houses, it is true, had been blown up in several places during the Fire in order to protect the Tower of London and Whitehall, but the use of gunpowder to raise a definite weight, and throw it a fixed distance and no farther, was a novel experiment. When the labourers reached at last the old central tower, the walls of which were two hundred feet high, they were afraid to go up to the top, as they had done elsewhere, and work with their pickaxes, while those below shovelled away the stones and mortar that they threw down into separate heaps. This was the time for Wren's experiment. With great precautions, and the use of eighteen pounds of gunpowder only, he blew up the north-western angle of the tower, so contriving it that, while he raised more than three thousand tons weight, it was not scattered and no damage was done, though the shock made the neighbours imagine it to be an earthquake. Encouraged by this success, Wren had another mine prepared, but unluckily was obliged to go out of town himself and to leave it in the charge of his next officer.