BA is equal to the angle CA. From this knowledge was derived the art of perspective, or that of designing on a plane the representations of various objects, as they would appear to the eye from a given point ;- -an art which was re-invented about the end of the fifteenth century.

The ancients seem also to have been conversant with the laws of the reflection of objects from the surface of water and polished metals. The earliest application of their knowledge in this way with which we are acquainted is that of the burning mirrors employed by Archimedes, a philosopher of Syracuse, about two hundred years before the Christian era. At the siege of that city by Marcellus, the Roman consul, he employed them to destroy the navy of the assailant. The method he

adopted is thus described by the historian Tzetzes :"When the fleet of Marcellus was within bow-shot, the old man, Archimedes, brought an hexagonal mirror, which he had previously prepared, at a proper distance from which he also placed other smaller mirrors of the same kind that moved in all directions on hinges, which, when placed in the sun's rays, directed them upon the' Roman fleet, whereby it was reduced to ashes." We are also informed that Proclus in the same way destroy the fleet of Vitellius, at the siege of Byzantium.

RS.

on this knowledge , or that of designing various objects, as they

a given point;--an art terd of the fifteenth

been conversant with ets from the surface of e earliest application of ..hich we are acquainted yed by Archimedes, hundred years bee of that city by employed them to The method he istorian setzes :--