it comes from their hands, shall be absolutely perfect; and whoever looks at the result, as they now attain it, will admit that they carry out their determination in a very successful manner. CINDER HOLES. Various other improvements have been made from time to time in the mode of manufacturing and finishing the musket, which have led to the condemnation or alteration of those made before the improvements were introduced. A striking illustration of this is afforded by the case of what are called _cinder holes_. A cinder hole is a small cavity left in the iron at the time of the manufacture of it--the effect, doubtless, of some small development of gas forming a bubble in the substance of the iron. If the bubble is near the inner surface of the barrel when it is welded, the process of boring and finishing brings it into view, in the form of a small blemish seen in the side of the bore. At a former period in the history of the Armory, defects of this kind were not considered essential, so long as they were so small as not to weaken the barrel. It was found, however, at length that such cavities, by retaining the moisture and other products of combustion resulting from the discharge of the piece, were subject to corrosion, and gradual enlargement, so as finally to weaken the barrel in a fatal manner. It was decided therefore that the existence of cinder holes in a barrel should thenceforth be a sufficient cause for its rejection, and all the muskets manufactured before that time have since been condemned and sold; the design of the department being to retain in the public arsenals only arms of the most perfect and unexceptionable character. At the present time, in the process of manufacturing the barrels, it is not always found necessary to reject a barrel absolutely in every case where a cinder hole appears. Sometimes the iron may be forced in, by a blow upon the outside, sufficiently to enable the workman to bore the cinder hole out entirely. This course is always adopted where the thickness of the iron will allow it, and in such cases the barrel is saved. Where this can not be done, the part affected is sometimes cut off, and a short barrel is made, for an arm called a musketoon. THE GRINDING.