The question is very frequently asked as to how the necessary registration of the colours is secured; it may be stated for the benefit of the amateur that in hand printing this is generally done by pricking with a pair of needles through printed marks present on each stone; but in the machine this has been done in different ways, although in quite early days "pointing" or "needling" was done even on the machine. On modern machines this registration depends on the accurate cutting of the edge of the paper, of which at least one corner must be an absolute right angle. The paper is then laid on a sloping board in such a way that the longest of the two true edges gravitates into the gripper of the machine, the stops of which move slightly forward as the gripper closes; simultaneously what is called the "side lay" moves forward automatically to a given extent, and in this way at the critical moment the sheet is always in the same position in regard to the stone, which has already been firmly secured in the bed of the machine. Quite recently a new method has come into use that is probably destined to be a great aid to the craft in its competition with other methods. This is known as offset printing; it is more a matter of evolution than invention, and proceeds from the method adopted in tin-plate decoration so much used for box-making and lasting forms of advertisement. It consists in bringing a sheet of rubber into contact with the charged stone and then setting-off the impression so obtained upon card, paper, pegamoid, cloth or other material, the elasticity of the rubber making it possible to print upon rough surfaces that have been previously unsuited to lithographic printing. Both flat bed and rotary machines are available for this system, the latter being restricted to zinc or aluminium plates, but giving a high speed, while the former can use both stones and metal plates and may be more effective for the highest grade of colour work; by both classes of machines the finest engraved note headings can be printed on rough paper, and colour work that has for so long been confined to coated or burnished papers will be available on surfaces such as the artists themselves use. The following treatises may be referred to with advantage by those in search of more detailed information: _A Complete Course of Lithography_, by Alois Senefelder (R. Ackermann, London, 1819); _The Grammar of Lithography_, by W. D. Richmond (13th edition, E. Menken, London); _Handbook of Lithography_, by David Cumming (London, A. & C. Black). The first of these will only be found in libraries of importance; the others are present-day text-books. (F. V. B.)