Exactness of body could be secured with little difficulty if all the types belonging to the same font were of the same width, and could be cast in one fixed and unalterable mould. But types of the same font and same body are of all widths. They vary, in the letters from the l to the W; in the spaces or blanks used to separate the words, from the hair space to the three-em quadrat. The spaces in the following illustrations are of the same body, but they are of different widths, to suit the peculiarities of different kinds of printed matter. [Illustration: Six-in-em Five-in-em Four-in-em Three-in-em space. space. space. space. En Em Two-em Three-em quadrat. quadrat. quadrat. quadrat.] It is not practicable to make a mould for each character; the cost would be enormous, and the multiplicity of moulds [p057] would lead to fatal faults in inaccuracy of body. Exactness of body can be had only by casting all the characters in one mould, but this mould must be made to suit all the matrices. The matrices must be frequently changed, but with such nicety that the types of every letter shall be uniform in height, in line, and truly square. Any mechanic will see that the construction of an adjustable mould is work of difficulty, and that the fitting-up of a set of matrices for one mould is a very nice operation. [Illustration: Figure 1. Type-Mould, without Matrix and with a Type in the Mould.] [Illustration: Figure 2. One Half of the Mould.] [Illustration: Figure 3. The Other Half of the Mould.] The Type-Mould of modern type-founders consists of two firmly screwed combinations of a number of pieces of steel, making right and left halves. In the first illustration of the mould, Figure 1, the halves are properly connected. In this form it is not practicable to represent the interior, but it may be understood that the interior faces fit each other snugly in every part but the centre, in which provision is made for a small opening which can be increased or diminished in a lateral direction only. One end of this opening is closed by the matrix; the other end is the jet, or the mouth-piece through which the melted metal is injected. In this opening, which is indicated by the letter H in the cut, the body of type is cast. The matrix which forms the face of the type is snugly fitted between the jaws on [p058] either side of this letter H. It does not appear in the cut; for the matrices, although indispensable parts, are always looked upon by founders as attachments to the mould.