The very heavy pieces of the 14th and 15th centuries were fired from positions on the ground. Some rested in heavy wooden cradles that could be wedged up at the muzzle end to increase the elevation; while the recoil was taken by timbers braced against short piles or stakes driven into the earth. By the end of the 14th century the cradle of some of the lighter siege pieces was mounted on wheels and they began to be employed in ordinary field operations. In the 15th century, the cradle was separated from the carriage frame and trail and fitted with an axle directly above the axle of the wheels. The rear end of the cradle passed between two upright timbers on the trail and was held at the desired elevation by a pin passing through the timbers and the cradle-end. In the 16th century, trunnions were cast on the gun and the cradle discarded. By this time mobile artillery had become an im portant part of all armies. Bad roads and soft ground emphasized the necessity for lightness in field guns, heavy pieces being necessarily left behind in a rapid advance or retreat. The tendency toward decreased weight cul minated in the kalter or "leather') gun of Gustavus Adolphus. This consisted of a cyl inder of copper banded with iron and wound with rawhide rope. It was a feeble piece of artillery but it could accompany mounted troops and could be loaded and fired two or three times as fast as the musket of that day. Increasing knowledge of the metallurgy of iron led, in the 16th century, to the production of cast-iron guns though bronze guns continued to be made, especially for field service, during the next 300 years. The advent of cast iron was accompanied by a change from breech to muzzle loading, a general reduction in calibre and weight, and an increase of muz zle velocity and gun-power. In the 16th and 17th centuries a few rifled cannon and small arms were made, but difficulties with the pro jectiles and the change to muzzle-loading caused the attempts at rifling to be given up.
The growing power of guns and greater regularity of range due to better powder led to a desire for more accurate pointing, especially in elevation. Adequate lateral direction could be effected by sighting along the !line of or median line of the top of the piece and this was further facilitated by notches cut on the upper side of the muzzle or breech. But the elevation could not be so easily deter mined until, about 1550, Tartaglia devised the °gunner's This consisted of a de vice resembling a carpenter's square on which was secured the graduated quadrant of a circle. The centre of this quadrant was at the angle of the square where the end of a plumb line was secured. The long arm of the square was inserted in the bore and as the gun rose in elevation the angle was shown by the plumb line and quadrant. About 1600 a dispart sight was used for short ranges. This consisted of a block set on the muzzle, the notch in the top of the block being at the same distance from the axis of the bore as the notch in the base ring of the gun-breech. During the 17th cen tury guns commenced to take on a more defi nite form. Pieces of great size and calibre were given up. Classification was attempted.
Although many names were applied to guns of different size, ordnance was beginning to be designated by type and weight of the solid iron shot which it fired. Four types of cannon were now in use in British naval vessels — (a) culverins, long slender guns; (b) cannons of battery, shorter and stockier pieces; (c) pet rieros, guns firing stone balls with rather small charges; (d) small pieces with various names such as minion, saker, falcon, falconet, etc. Each type was made in three lengths, extraor dinary, ordinary and bastard; thus, extraor dinary culverins were 39 to 41 calibres in length; ordinary, 32; bastard, 26 to 28. Land guns were similarly named and classed but they also included the mortar and the trabuccho (which differed from the mortar only in having the trunnions at the breech end instead of in the middle. Whole culverins fired shot of 40 to 60 pounds or more; culverins, 20 to 35 pounds; demi-culverins, 14 to 18; whole cannon, 70 to 120 pounds; cannon, 30 to 50; demi-can non, 20 to 28; quarter-cannon, 16 to 18; saker, or quarter culverin, 8 to 12; falcon or half saker, 5 to 7; falconet, 2 to 4; rabinet, or smeriglio, 1,4 to 1.
In the 17th century, naval guns were gradu ally reduced to two types; long (18 to 25 cali bres in length), and short (about 15 calibres). Near the end of the century, carronades be gan to be used, particularly for upper deck guns. They were very short (5 or 6 calibres) and light, but fired large projectiles—of course with low velocity. Naval actions were usually fought at such very short ranges that a gun of this type was often exceedingly efficient. The heaviest naval guns were 42-pounders, but few pieces larger than the 32-pounders were carried and these by ships of the line. The gun-carriages were constructed with heavy wooden sides called brackets joined by similar flat timbers called transoms — the whole supported on wooden trucks 6 to 10 inches in diameter. The trunnions of the gun rested in trunnion sockets in the tops of the brackets. At the end of the 17th century, land guns for sea-coast fortifications were simi lar to the long naval pieces. Field guns were of three principal types, cannon (15 to 25 calibres long), howitzers (8 to 10 calibres) and mortars (3 to 5 calibres). During the 18th century many important improvements were made in ordnance and gunnery. About 1739 the French devised the plan of casting the gun solid and boring it out. This added nothing to the strength but much improved the accuracy. In 1742, Benjamin Robins, an English mathe matician and military engineer, published his work entitled Principles of Gunnery' which revolutionized ordnance and gunnery and founded the science of ballistics. In conduct= ing his researches Robins invented the ballistic pendulum, determined the path of projectiles in the air and investigated the air-pressure against them. He pointed out the desirability of rifling guns and expressed in strong terms the advantages which would accrue to any nation which would first succeed in arming itself with efficient weapons of this type.