The general principle of all perforating machines is a series of hollow needles, which remove rows of small disks of the paper from between the stamps, and thus fit them to be readily torn apart. For convenience of reference and description philatelists have adopted, as a standard of measurement, the space of two centimetres. The gauge of a perforation is determined by the number of holes in this distance. Scales have been prepared for measuring perforations but it would be superfluous to attempt to describe them here. One of the largest perforations that has been used for stamps has seven holes in two centimetres. This was used on the stamps of France by Susse Freres, a firm of stationers. It was done for the convenience of themselves and their customers. Some of the stamps of Mexico have a still larger perforation gauging 51/2. The finest gauge is about 19. This is an unofficial perforation and was applied to some of the early stamps of Tasmania. [Illustration: Perforation] [Illustration: Perforation] [Illustration: Perforation] [Illustration: Perforation] We show you here a variety of perforations. The first two are ordinary perforations of different gauges, 91/2 and 14. The third shows a perforation in square holes instead of round. The next is an example of pin perforation, the holes being far apart and small. Two sides of the stamp show the holes before the stamps have been torn apart and a third side shows the ragged effect produced by separating them. Another form of pin perforation is made by needles which are not hollow and merely prick holes in the paper without removing any of it. This sort of perforation has sometimes been made by a sewing machine with an unthreaded needle. [Illustration: Perforation] The last form of perforation shown is called lozenge. In this the machine removes small diamond shaped pieces from the paper. The effect before the separation is shown between the pair of stamps, while the outer edges show the appearance of single copies. [Illustration: Perforation] A variety of machines are used in perforating stamps. One perforates only a single row of holes at a time. This is known as the guillotine machine because its action suggests that unpleasant instrument. Another machine is called the comb machine because the needles are arranged to perforate across the top of a row of stamps and at the same time between the stamps of that row. This arrangement somewhat resembles a comb. It will be seen that the first application perforates the stamps of one row on three sides. The application of the machine to the next row below completes the fourth side. In the best perforating machines the needles are arranged in circles around a spindle. The sheets pass under this roller and are perforated in one direction. A similar machine makes the perforations in the other direction.