The 21st the besiegers’ batteries ceased firing to allow of a summons, but the governor refused to receive the letter and the firing was resumed. The main wall still resisted yet the parapets and embrazures crumbled away fast, and the batteries on Monte Olia plunged into the horn-work, although at sixteen hundred yards distance, with such effect, that the besieged having no bomb-proofs were forced to dig trenches to protect themselves. The counter-fire directed solely against the breaching batteries was feeble, but at midnight a shell thrown from the castle into the bay gave the signal for a sally, and during the firing which ensued several French vessels with supplies entered the harbour. This night also the besieged isolated the breach by cuts in the rampart and other defences. On the other hand the besiegers’ parallel across the isthmus was completed, and in its progress laid bare the mouth of a drain, four feet high and three feet wide, containing the pipe of the aqueduct cut off by the Spaniards. Through this dangerous opening lieutenant Reid of the engineers, a young and zealous officer, crept even to the counterscarp of the horn-work, and finding the passage there closed by a door returned without an accident. Thirty barrels of powder were placed in this drain, and eight feet was stopped with sand-bags, thus forming a globe of compression designed to blow, as through a tube, so much rubbish over the counterscarp as might fill the narrow ditch of the horn-work. [Sidenote: Plan 3.] On the 22d the fire from the batteries, unexampled from its rapidity and accuracy, opened what appeared a practicable breach in the eastern flank wall, between the towers of Los Hornos and Las Mesquitas. The counter-fire of the besieged now slackened, but the descent into the town behind the breach was more than twelve feet perpendicular, and the garrison were seen from Monte Olia diligently working at the interior defences to receive the assault: they added also another gun to the battery of St. Elmo, just under the Mirador battery, to flank the front attack. On the other hand the besiegers had placed four sixty-eight pound carronades in battery to play on the defences of the breach, but the fire on both sides slackened because the guns were greatly enlarged at the vents with constant practice.