OP ROCKETS. 213 



To give the cartridges the same length and thickness, in order 

 that any number of rockets may be prepared of the same size and 

 force, they are put into a hollow cylinder of strong wood, called a 

 mould. This mould is sometimes of metal ; but at any rate it 

 ought to be made of some very hard wood. 



This mould must not be confounded with another piece of wood, 

 called the former or roller, aruund which is rolled the thick pfper 

 employed to make the cartridge. If the calibre of the mould be 

 divided into 8 equal parts, the diameter of the roller must be equal 

 to 5 of these parts. The vacuity between the roller and the inte- 

 rior surface of the mould, that is to say of the calibre of the 

 mould, will be exactly Ailed by the cartridge. 



As rockets are made of different sizes, moulds of different lengths 

 and diameters must be provided. The calibre of a cannon is nothing 

 else than the diameter of its mouth ; and we here apply the same 

 term to the diameter of the aperture of the mould. The size of the 

 mould is measured by its calibre ; but the length of the moulds for 

 different rockets does not always bear the same proportion to the 

 calibre, the length bi ing diminished as the calibre is increased. 

 The length of the mould for small rockets ought to be six times the 

 calibre, but for rockets of the mean and larger size, it will be suffi- 

 cient if the length of the mould be five times or four times the 

 calibre of the moulds. 



At the end of this chapter we shall give two tables, one of which 

 contains the calibres of moulds below a pound bullet ; and the 

 other the calibres from a pound to a hundred pounds bullet. 



For making the cartridges, large stiff paper is employed. This 

 paper is wrapped round the roller, and then cemented by means of 

 common paste. The thickness of the paper when rolled up in this 

 manner, ought to be about one-eighth and a half of the calibre of the 

 mould, according to the proportion given to the diameter of the 

 roller. But if the diameter of the roller be made equal to the 

 calibre of the mould, the thickness of the cartridge must be a twelfth 

 and a half of that calibre. 



When the cartridge is formed, the roller is drawn out, by turn, 

 ing it round, until it is distant from the edge of the cartridge the 

 length of its diameter. A piece of cord is then made to pass twice 

 round the cartridge at the extremity of the roller. And into the 

 vacuity left in the cartridge, another roller is introduced, so as to 

 some space between the two. On end of the pack. thread 



