rays passing on from the image through the eye-glass S, and through a small hole e in the end of the lesser tube t t, they enter the eye f which sees the [Page 291] image a d (by means of the eye-glass), under the large angle c e d, and magnified in length, under that angle, from c to d. To find the magnifying power of this telescope, multiply the focal distance of the great mirror by the distance of the small mirror, from the image next the eye, and multiply the focal distance of the small mirror by the focal distance of the eye-glass; then divide the product of the latter, and the quotient will express the magnifying power. (Fig. 280.) We now come to that much disputed and often quoted experiment of Archimedes, who is stated to have employed metallic concave specula or some other reflecting surface by which he was enabled to set fire to the Roman fleet anchored in the harbour of Syracuse, and at that time besieging their city, in which the great and learned philosopher was shut up with the other inhabitants. The story handed down to posterity was not disputed till about the seventeenth century, when Descartes boldly attacked the truth of it on philosophical grounds, and for the time silenced those who supported the veracity of this ancient Joe Miller. Nearly a hundred years after this time, the neglected Archimedes fiction was again examined by the celebrated naturalist Buffon, and the account of his experiments detailed by the author of "Adversaria," in Chambers' Journal, is so logical and conclusive, that we give a portion of it verbatim. "For some years prior to 1747, the French naturalist Buffon had been engaged in the prosecution of those researches upon heat which he afterwards published in the first volume of the Supplement to his 'Natural History.' Without any previous knowledge, as it would seem, of the mathematical treatise of Anthemius ([Greek: _peri paradoxôn mêchanêmatôn_]), in which a similar invention of the sixth century is described,[G] Buffon was led, in spite of the reasonings of Descartes, to conclude that a speculum or series of specula might be constructed sufficient to obtain results little, if at all, inferior to those attributed to the invention of Archimedes. [Footnote G: See Gibbon's "Decline and Fall," chap. xl., section v., note _g_.]