This summer the distinguished officer who commanded the 143d regiment of Pennsylvania volunteers, United States army, at the battle of Gettysburg, informed me that during the last day of the battle, he and his men frequently heard, above their heads, amid the whistling of the minnie balls from the Confederate side, sharp, explosive sounds like the snapping of musket caps. He mentioned the matter to an ordnance officer at the time. The officer replied that what he heard was explosive rifle balls, which the Confederates had captured from the Union troops, who had lately received them from the Ordnance Department. From the fact that the Gardiner shell is not fitted with a percussion cap at the point of the projectile, and is not easily exploded by hand, and from the additional fact that only about ten thousand are reported as having been used in action, I am willing to believe that the primary purpose of the Government of the United States in using them was the exploding of caissons. There is, moreover, no evidence that any of these shells were issued from the Ordnance Bureau after the year 1863. The Gardiner shells are so constructed as to have no different appearance in the cartridge from the common minnie ball--only the title on the box, and an examination of the ball when separate from the cartridge, giving any indication of its explosive character. I know not _certainly_ if any other such projectiles were used by the United States troops, nor have I any especial desire to prosecute the investigation further than to prove the position taken in this paper. It would be disingenuous in me if I failed to notice the fact that a charge somewhat similar to that which begins this article was made by a correspondent in the _Scientific American_ for September 6th, 1862, volume VII, page 151, as follows: Recently it was my privilege to examine, in the hands of a man just from Fortress Monroe, an explosive bullet, such as was used by the Rebels in the six days' battle. It is conical in shape, about one inch long, made of lead, and consists of two parts--viz: a solid head piece and a cylindrical chamber, which are united together by a screw. From the point of the bullet projects a little rod, which passes down through a small hole in the head piece into the chamber below, where it was connected with a percussion cap. The chamber contains about a tablespoonful of powder. You can readily perceive that if the bullet should encounter a bone or other hard substance when entering a man's body, it will explode and thereby produce a fatal wound. F. J. C. PHILADELPHIA, August 23, 1862. In the Patent Office Report (United States) for 1863-4 will be found a shell exactly corresponding to this one: No. 39,593--Joseph Nottingham Smith, New York, N. Y.--_Improvement in Elongated Projectile for Firearms_--Patent dated August 18, 1863.