140 MILITARY SCIENCES. 



charge. At the instant when the rocket is lighted the stick, U, is kindled 

 also, and the hand-grenades are thrown out, one after another, as it flies. 



To give the rockets a specific direction various apparatus are employed ; 

 Jig. 54 shows one variety. Here is a tube, to which, as soon as the rocket 

 is placed in it, the base cylinder, R X T V, is screwed fast, whose floor has 

 a round orifice, U, for the stick of the rocket ; e e are four cuts in the cir- 

 cumference of the cylinder, and above these is a ring-formed groove. When 

 the rocket is placed in the tube, the ring Imvr is slipped over the stick o 

 {fig. 55 gives a view of this ring with the flanges /, m, n, p), its flanges 

 shoved through the cuts e e and then turned, so as to catch in the groove, 

 whereby the tube is closed below ; r v are small pipes for the priming. 

 Fig. 56 is a rocket wagon : upon the under-frame, A, lies a bed, B, upon 

 which stands the chest, C, in which are kept the rockets without stick. 

 The sticks are fastened upon the bed and only attached to the rockets as 

 wanted for use. E is the principal trestle, with the socket G, for the rocket 

 H, for which a graduated curve, F, gives the elevation. The stick J rests 

 upon the second upright D, in which a slide, K, is movable for the support 

 of the stick. Fig. 57 is the upper part of Congreve's rocket- wagon : upon 

 the beam D slides, by means of the roller G, the bed A, on which, at B, is 

 a hinge-joint, receiving the tube E H, which is fastened at F, and can be 

 set higher or lower by means of the movable brace, C ; in this tube the 

 rocket stick is inserted. 



E. SCIETfCE OF FORTIFICATION. 



The Science of Fortification teaches so to prepare any point of ground by 

 artificial means that upon it a small number of persons can maintain them- 

 selves against the attacks of a superior force. The point in question may 

 be fortified only for a short time, or it may be desired to prepare it, in time 

 of peace even, to sustain a regular siege ; and according to these different 

 objects fortification is divided into temporary or field fortification, and fixed 

 or permanent fortification. The art of fortification has been practised ever 

 since the weak have had to defend themselves against the strong, and we 

 may divide it, for our consideration, into three periods. 



ANTiaUITY. 



The first attempts to build stone walls were rude ; the stones were piled 

 one upon another, just as they were found, and the interstices of the larger 

 filled up with smaller ones. Soon they progressed so far as at least to hew 

 the front of the stone and give the wall an even exterior. Gates and open- 

 ings in such walls were at first very simply made, and pi 42, fig. 2, gives a 

 picture not only of the oldest Cyclopean wall of Tiryns, but shows also how 

 the gate openings were covered only with one larger stone. These open- 

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