The giant Blakely gun at Charleston.This was an English gun, all steel, to which the principle of “initial tension” was successfully applied. From the breech to the trunnions of the Blakely gun it was pear-shaped, for the purpose of resisting the tremendous power-pressures. By “initial tension” is meant intentional strain in the metal of the gun, scientifically placed, so as to counteract in a measure the strains set up by the powder discharge. There is an inner tube, on the outside of which bands are shrunk so as to set up a strain of extension in the exterior band. By properly combining these strains the extreme tension due to the powder gases at their moment of greatest expansion does not affect the gun as injuriously as if these initial strains were not present. This was among the earliest form of cannon to be successful with this principle of “initial tension,” a fundamental element in the scientific design of the best modern built — up guns.