Soult was now growing vexed at the delay, and sent two guns of position from Oporto to Loison, to enable him to subdue the fire of the enemy’s batteries. He also offered to call up Heudelet’s division from Braga, even at the cost of abandoning his hold on the northern part of the province of Entre-Douro-e-Minho. But a mere increase of his already considerable force would have been of no service to Loison; it was a device for passing the Tamega that he needed. Such a scheme was at last laid before him by Captain Bouchard, one of his engineers[318]. The French officers had discovered, by a careful use of their glasses, that the Portuguese mine, which was to destroy the bridge, was situated in its left-hand arch, and that the mechanism by which it was to be worked was not a ‘sausage’ or a train of powder[319], but a loaded musket, whose muzzle was placed in the mine, while to its trigger was attached a cord which ran to the nearest trenches beyond the river. The musket was concealed in a box, but its cord was visible to those provided with a good telescope. Bouchard argued that if the cord could be cut or broken, the enemy would not be able to touch off the mine, and he had thought out a plan for securing his end. He maintained that an explosion at the French side of the bridge would probably sever the cord without firing the mine, and that a sudden assault, made immediately after the explosion, and before the Portuguese could recover themselves, might carry the barricades. In spite of the strongly-expressed doubts of Foy and several other generals, Bouchard was finally permitted to carry out his scheme. [318] Napier, ii. pp. 80-1, consistently mis-calls him Brochard. [319] Either of these might easily have been fired by a casual shot, during the long cannonading which had been in progress. The Portuguese, therefore, avoided them.