The instruments used for writing would, of course, be such as were adapted to the material on which they were to be employed. For writing upon the brazen, leaden, or waxed tablets, above mentioned, a needle, called a style, was used, the upper end of which, being smooth and flat, served to obliterate the marks on the tablet, as occasion might require. These styles were at first most often formed of iron or brass; but afterwards of ivory, bone, or wood. Indeed a fatal use having been, on several occasions, made of these pointed weapons by angry partisans in the public courts, the use of iron styles was prohibited; Cæsar, when attacked by the conspirators, is said to have used his iron style as a dagger, and with it to have pierced the arm of one of them: and the story of the Christian schoolmaster, Cassianus, is well known, who is said to have been killed by his scholars, armed with their styles: other similar instances are recorded. For the purpose of writing with fluid ink, a calamus, formed generally from a reed of the Nile, was used. Persons of distinction often wrote with a calamus of silver. The use of quills seems to have been of ancient date; but long after the time when the fitness of the quill for the purpose of writing had become known, the calamus of reed continued to be preferred. The scalpel, or knife employed for trimming the pen, the compasses, for measuring the distances of the lines, and the scissars, for cutting the paper, are always seen on the desk of the writers in the decorations attached to many ancient manuscripts. The ink most used by the ancients has been said, but on rather uncertain authority, to have consisted of the black liquor found in the cuttle fish. But it has been proved by chemical analysis that an opaque ink, very different from the mere dye or stain used at present, was commonly employed by the transcribers of books. This opaque ink seems, like the China ink, to have been formed from the finest soot of lamps, in which the purest combustibles were burnt. The coal of ivory, or of the finer woods, powdered, was also in use; these or similar substances, mixed with gums, and diluted with acids, formed a pigment that was much more durable than our modern ink; but it was also far less fluent, and therefore less adapted to a rapid and continuous movement of the pen.