13. Why is a piece made stronger near the breech than towards the muzzle? Because the elastic force of the inflamed gunpowder is there greatest, constantly diminishing in intensity as the space increases in which it acts. 14. What is the length of a piece? The distance from the rear of the base-ring to the face of the piece. [Sidenote: 12]] 15. What is the extreme length? From the rear of the cascable to the face. 16. What is the _bore_ of a piece? It includes the part bored out, viz: the cylinder, the chamber (if there is one), and the conical or spherical surface connecting them. 17. What is understood by the _calibre_ of a piece? The diameter of the bore. 18. How do you ascertain the number of calibres in a piece? Divide the length of the cylinder, in inches, by the number of inches in the calibre. 19. The number of calibres being known, how do you find the length of the cylinder? Multiply the number of calibres by the calibre in inches. 20. What is meant by the _sights_ of a piece? Artificial marks on the piece for determining the line of fire. 21. How are the sights determined? Usually by means of the gunner’s level, when the trunnions are perfectly horizontal. 22. What is the _line of metal_ or the natural line of sight? It is a line drawn from the highest point of the base-ring to the highest point on the swell of the muzzle. 23. What is the _axis_ of a piece? An imaginary line passing through the centre of the bore. 24. What is the _natural angle of sight_? It is the angle which the natural line of sight makes with the axis of the piece. [Sidenote: 13]] 25. What is the _dispart_ of a piece? It is the difference of the semi-diameter of the base-ring and the swell of the muzzle, or the muzzle-band. It is, therefore, the tangent of the natural angle of sight to a radius equal to the distance from the rear of the base-ring to the highest point of the swell of the muzzle, or the front of the muzzle-band, as the case may be, measured parallel to the axis. 26. Give the nomenclature of a piece? The CASCABLE is the part of the gun in rear of the base-ring, and is composed generally of the _knob_, the _neck_, the _fillet_, and the _base of the breech_. The BASE OF THE BREECH is a frustum of a cone, or a spherical segment in rear of the breech. The BASE-RING is a projecting band of metal adjoining the base of the breech, and connected with the body of the gun by a concave moulding. The BREECH is the mass of solid metal behind the bottom of the bore, extending to the rear of the base-ring. The REINFORCE is the thickest part of the body of the gun, in front of the breech; if there be more than one _reinforce_, that which is next the breech is called the _first reinforce_; the other the _second reinforce_. The REINFORCE BAND is at the junction of the first and second reinforces in the heavy howitzers and columbiads. The CHASE is the conical part of the gun in front of the reinforce.