While barricades were being built at Rivas and the town was more thoroughly prepared for defence, Col. Swingle was engaged in labors which added much to the efficiency of the artillery. The mechanical genius of Swingle was extraordinary. Besides the well-organized work-shops he established at Rivas, he got a small engine from San Juan del Sur and succeeded in producing a blast of air which enabled him to smelt iron, and thus he cast the first cannon-balls ever made in Central America. The scanty supply of balls had been a serious obstacle to the employment of the artillery, and for some time it was necessary to use such as could be moulded with lead. As the supply of lead was limited, it would not do to put a great deal of it into the shape of cannon balls. A number of bells had been gathered from the towns and villages of the Meridional Department, and from these Swingle cast round shot, more effective, though also dearer, than those made of iron. On the morning of the 7th of February, a supply of round shot having been procured, Henningsen, supported by the Rifles, proceeded to San Jorge to give the enemy a cannonade. He prepared some empty musket-boxes in order to construct a breastwork rapidly and without annoyance from the enemy. While it was yet dark he reached a point about six hundred yards from the lines of the Allies, and before daybreak his work was so far complete as to enable the men to proceed without interruption by the fire from the Plaza. The breastwork being finished, the six-pounders were fired rapidly and with much accuracy. The impression made on the Allies was apparent, though they affected to say that the balls did small damage. None of the Americans was hurt, and they returned to Rivas in good spirits at the work which had been done with so little expense. The object of these frequent attacks on the enemy was to keep them in a state of constant alarm, and besides the actual loss of the Allies in killed and wounded, the confusion into which they were thrown by the appearance of the Americans always enabled a few of the soldiers to desert. It was important, also, for Walker—while waiting the result of Lockridge’s effort to open the Transit—to let his troops see that they were not thrown entirely on the defensive.