In other places boats were run under overhanging trees on the shore, in which signal flags were hoisted, and the angles measured below with sextants. It was very satisfactory, however, that the last measurement determined (leading to the flagstaff on St. Philip) agreed almost identically with the location given by the coast survey several years ago. It seemed to be a regular occupation of the garrison in the fort, to destroy, during the night-time, the marks and signals which were left daily by the party; and for this reason, Mr. Gerdes caused numbered posts to be set in the river banks, and screened with grass and reeds so that they could not be found by the enemy in the dark. From these marks, which were separately determined, he was enabled to furnish to Captain Porter the distances and bearings, from almost any point on the river to the forts, and by the resulting data the commander selected the positions for his mortar vessels. On the 17th day of April the mortar schooners were moved to their designated positions, and the exact distances and bearings of each vessel being ascertained from the map, were furnished to the respective captains. Then the bombardment fairly commenced, and was continued, with only slight intermission, for six days. Twice Captain Porter ordered some of the vessels to change their positions when he found localities that would answer better; the coast survey party furnished the new data required. From the schooners, which were fastened to the trees on the riverside, none of the works of the enemy were visible, but the exact station of each vessel and its distance and bearings from the forts had been ascertained from the chart. The mortars were accordingly charged and pointed and the fuses regulated. Thus the bombardment was conducted entirely upon theoretical principles, and as such with its results, presents perhaps a new feature in naval warfare. When the whole number of shells discharged from the flotilla is compared with those that fell and left their marks on the dry parts of Fort Jackson (to which must be added, in the same ratio, all those falling in the submerged parts), the precision of the firing appears truly remarkable, and must command our highest admiration, particularly when we consider that every shot was fired upon a _computed_ aim.