[Footnote 8: The most plausible reason assigned is that of the expansion of the tube toward the fire by the influence of the heat. The fallacy of this theory is at once shown by the fact that, although heat does expand bodies, it does not increase their weight; therefore, notwithstanding that one side of the tube may be expanded, its equilibrium will remain unimpaired.] It is not surprising that marvels and paradoxes should be related of glass, considering the almost incredible properties it really possesses. Seeing that it emits musical sounds when water is placed in it, and it is gently rubbed on the edges; that these sounds can be regulated according to the quantity of water, and that the water itself leaps, frisks, and dances, as if it were inspired by the music; seeing its extraordinary power of condensing vapor, which may be tested by simply breathing upon it; and knowing that, slight and frail as it is, it expands less under the influence of heat than metallic substances, while its expansions are always equable and proportioned to the heat, a quality not found in any other substance, we can not be much astonished at any wonders which are superstitiously or ignorantly attributed to it, or expected to be elicited from it. One of the most remarkable is the feat ascribed to Archimedes, who is said to have set fire to the Roman fleet at the siege of Syracuse by the help of burning-glasses. The fact is attested by most respectable authorities,[9] but it is only right to add, that it is treated as a pure fable by Kepler and Descartes, than whom no men were more competent to judge of the possibility of such an achievement. Tzetzez relates the matter very circumstantially; he says that Archimedes set fire to Marcellus's navy by means of a burning glass composed of small square mirrors, moving every way upon hinges; which, when placed in the sun's rays, directed them upon the Roman fleet, so as to reduce it to ashes at the distance of a bow-shot. Kircher made an experiment founded upon this minute description, by which he satisfied himself of the practicability of at least obtaining an extraordinary condensed power of this kind. Having collected the sun's rays into a focus, by a number of plain mirrors, he went on increasing the number of mirrors until at last he produced an intense degree of solar heat; but it does not appear whether he was able to employ it effectively as a destructive agent at a long reach. Buffon gave a more satisfactory demonstration to the world of the capability of these little mirrors to do mischief on a small scale. By the aid of his famous burning-glass, which consisted of one hundred and sixty-eight little plain mirrors, he produced so great a heat as to set wood on fire at a distance of two hundred and nine feet, and to melt lead at a distance of one hundred and twenty, and silver at fifty; but there is a wide disparity between the longest of these distances and the length of a bowshot, so that the