MILITARY ENGINES. 125 



trunnion, D, of the mortar, an index is fixed, which shows, upon a circular 

 scale attached to the bed, the angle of elevation; a, is the pivot bolt for the 

 stool bed, h ; and c, the directing screw, the head of which fits into the stool 

 bed, h, while the female screw in which it plays lies in a movable transom 

 between the low cheeks. Fig. 22 is a side view of the stool bed : «, is the 

 socket for the spherical head of the directing screw; h, the cushion for the 

 mortars ; and c, the hole for the pivot bolt. 



A peculiar kind of mortar bed is that for the sea mortar {pi. 38, fig. 6, 

 side view ; jig. 7, upper view ; fig. 8, cross section on the half scale). These 

 beds are composed of two layers of oak beams, jJT and ee, each pair breaking 

 joints and bound together with the belts, gh and i. The studs, ff {fig. 7), 

 serve for giving the side direction. Upon this bed lies the iron sole plate, 

 which, by means of screw bolts through the disk, x, and by the screws of 

 the rings, ekno (which are for securing the mortar by ropes), is fastened to 

 the bed proper. In this sole plate the trunnion beds are sunk, and the cap 

 squares, m, secured upon them by key bolts. The sole plate and bed are 

 hollowed out at t, for the mortar and quoin. The whole bed stands, by 

 means of a groove, upon the circular iron platform, ah, and is so connected 

 with this by the pivot bolts, d (figs. 7 and 9), that both can revolve around 

 it for the side direction. The pivot bolt is secured into one of the beams 

 of the ship. 



f. The Elevating Screw. With cannon and howitzers, the muzzle 

 must be movable through a curve of ten or fifteen degrees, in order to give 

 the necessary elevation or depression for the aim ; for mortars, the eleva- 

 tion amounts even to sixty degrees. To effect these movements with the 

 requisite accuracy and rapiditj^ the elevating screw is employed. The 

 most simple means of accomplishing the purpose is by the quoin or wedge, 

 which was formerly used for cannon and howitzers by moving it in or out 

 under the base-ring. At present this is used only for mortars {pi. S7, fig. 8), 

 and for them three are employed. Under ]5° elevation, the mortar lies 

 upon the bed ; the first quoin gives 25°, the second, 30°, and thus with the 

 third 45° or 60'^ can be given. The screw quoin is better, indeed, as it 

 admits of moreiaccuracy in the elevation; but this, on account of its slow- 

 ness, is used only for garrison pieces. Fig. 25 shows the section of such a 

 quoin : a, is the wedge upon which the base-ring rests ; b, is the stool bed 

 lying between the bed cheeks, upon a groove in which the wedge moves by 

 means of the screw, d, which works in the female screw, c, firmly fixed in 

 the stool bed. The quoin of the Montalembert carriage is similar to this, 

 save that the screw in it is fixed and the female screw set in the wedge, 

 which is thus moved to and fro by turning the screw {fig. 26, side view of 

 this quoin ; fig. 27, longitudinal section ; fig. 28, front view). A, is the 

 quoin ; B, the screw, which is turned by the winch, C ; to the quoin the 

 plate, D, is fastened, which holds the thread of the female screw, and is 

 opened when the screw is to be taken out. Another kind of elevating 

 apparatus is that with a windlass {fig. 20), which was used for the Saxon 

 park cannon. The stool bed, B, which moves between the carriage cheeks, 

 AA, has two wings, aa, in front, by which it is attached to the trunnions, 



CGI 



