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TURNING.

After the boring, then, of the barrel, comes the turning of the outside of it. The piece is supported in the lathe by means of mandrels inserted into the two ends of it, and there it slowly revolves, bringing all parts of its surface successively under the action of a tool fixed firmly in the right position for cutting the work to its proper form. Of course the barrel has a slow progressive as well as rotary motion during this process, and the tool itself, with the rest in which it is firmly screwed, advances or recedes very regularly and gradually, in respect to the work, as the process goes on, in order to form the proper taper of the barrel in proceeding from the breech to the muzzle. The main work however in this turning process is performed by the rotation of the barrel. The workman thus treats his material and his tools with strict impartiality. In the boring, the piece remains at rest, and the tool does its work by revolving. In the turning, on the other hand, the piece must take its part in active duty, being required to revolve against the tool, while the tool itself remains fixed in its position in the rest.

Among the readers of this article there will probably be many thousands who have never had the opportunity to witness the process of turning or boring iron, and to them it may seem surprising that any tool can be made with an edge sufficiently enduring to stand in such a service. And it is indeed true that a cutting edge destined to maintain itself against iron must be of very excellent temper, and moreover it must have a peculiar construction and form, such that when set in its proper position for service, the cutting part shall be well supported, so to speak, in entering the metal, by the mass of the steel behind it. It is necessary, too, to keep the work cool by a small stream of water constantly falling upon the point of action. The piece to be turned, moreover, when of iron, must revolve very slowly; the process will not go on successfully at a rapid rate; though in the case of wood the higher the speed at which the machinery works, within certain limits, the more perfect the operation. In all these points the process of turning iron requires a very nice adjustment; but when the conditions necessary to success are all properly fulfilled, the work goes on in the most perfect manner, and the observer who is unaccustomed to witness the process is surprised to see the curling and continuous shaving of iron issuing from the point where the tool is applied, being cut out there as smoothly and apparently as easily as if the material were lead.

THE STRAIGHTENING.

One of the most interesting and curious parts of the process of the manufacture of the barrel, is the straightening of it. We ought, perhaps, rather to say the straightenings, for it is found necessary that the operation should be several times performed. For example, the barrel must be straightened before it is turned, and then, inasmuch as in the process of turning it generally gets more or less sprung, it must be straightened again afterward. In fact, every important operation performed upon the barrel is likely to cause some deflection in it, which requires to be subsequently corrected, so that the process must be repeated several times. The actual work of straightening, that is the mechanical act that is performed, is very simple—consisting as it does of merely striking a blow. The whole difficulty lies in determining when and where the correction is required. In other words, the making straight is very easily and quickly done; the thing attended with difficulty is to find out when and where the work is crooked; for the deflections which it is thus required to remedy, are so extremely slight, that all ordinary modes of examination would fail wholly to detect them; while yet they are sufficiently great to disturb very essentially the range and direction of the ball which should issue from the barrel, affected by them.

STRAIGHTENING THE BARRELS.

The above engraving represents the workman in the act of examining the interior of a barrel with a view to ascertaining whether it be straight. On the floor, in the direction toward which the barrel is pointed, is a small mirror, in which the workman sees, through the tube, a reflection of a certain pane of glass in the window. The pane in question is marked by a diagonal line, which may be seen upon it, in the view, passing from one corner to the other. This diagonal line now is reflected by the mirror into the bore of the barrel, and then it is reflected again to the eye of the observer; for the surface of the iron on the inside of the barrel is left in a most brilliantly polished condition, by the boring and the operations connected therewith. Now the workman, in some mysterious way or other, detects the slightest deviation from straightness in the barrel, by the appearance which this reflection presents to his eye, as he looks through the bore in the manner represented in the drawing. He is always ready to explain very politely to his visitor exactly how this is done, and to allow the lady to look through the tube and see for herself. All that she is able to see, however, in such cases is a very resplendent congeries of concentric rings, forming a spectacle of very dazzling brilliancy, which pleases and delights her, though the mystery of the reflected line generally remains as profound a mystery after the observation as before. This is, in fact, the result which might have been expected, since it is generally found that all demonstrations and explanations relating to the science of optics and light, addressed to the uninitiated, end in plunging them into greater darkness than ever.

The only object which the mirror upon the floor serves, in the operation, is to save the workman from the fatigue of holding up the barrel, which it would be necessary for him to do at each observation, if he were to look at the window pane directly. By having a reflecting surface at the floor he can point the barrel downward, when he wishes to look through it, and this greatly facilitates the manipulation. There is a rest, too, provided for the barrel, to support it while the operator is looking through. He plants the end of the tube in this rest, with a peculiar grace and dexterity, and then, turning it round and round, in order to bring every part of the inner surface to the test of the reflection, he accomplishes the object of his scrutiny in a moment, and then recovering the barrel, he lays it across a sort of anvil which stands by his side, and strikes a gentle blow upon it wherever a correction was found to be required. Thus the operation, though it often seems a very difficult one for the visitor to understand, proves a very easy one for the workman to perform.

OLD MODE OF STRAIGHTENING.

In former times a mode altogether different from this was adopted to test the interior rectitude of the barrel. A very slender line, formed of a hair or some similar substance, was passed through the barrel—dropped through, in fact, by means of a small weight attached to the end of it. This line was then drawn tight, and the workman looking through, turned the barrel round so as to bring the line into coincidence successively with every portion of the inner surface. If now there existed any concavity in any part of this surface, the line would show it by the distance which would there appear between the line itself and its reflection in the metal. The present method, however, which has now been in use about thirty years, is found to be far superior to the old one; so much so in fact that all the muskets