The warp is composed of silk, forming the body and groundwork on which the pattern in glass appears, as effected by the weft. The requisite flexibility of glass thread for manufacturing purposes is to be ascribed to its extreme fineness; as not less than from fifty to sixty of the original threads (spun by steam engine power) are required to form one thread of the weft. The process is slow; for no more than a yard of cloth can be produced in twelve hours. The work, however, is extremely beautiful and comparatively cheap, inasmuch as no similar stuff, where bullion is really introduced, can be purchased for anything like the price for which this is sold; added to this, it is, as far as the glass is concerned, imperishable. Glass is more durable than either gold or silver, and, besides, possesses the advantage of never tarnishing. CHAPTER VII. DESCRIPTION OF THE SILK-WORM, &c. Preliminary observations--The silk-worm--Various changes of the silk-worm--Its superiority above other worms--Beautiful verses on the May-fly, illustrative of the shortness of human life--Transformations of the silk-worm--Its small desire of locomotion--First sickness of the worm--Manner of casting its Exuviæ--Sometimes cannot be fully accomplished--Consequent death of the insect--Second, third, and fourth sickness of the worm--Its disgust for food--Material of which silk is formed--Mode of its secretion--Manner of unwinding the filaments--Floss-silk--Cocoon--Its imperviousness to moisture--Effect of the filaments breaking during the formation of the cocoon--Mr. Robinet’s curious calculation on the movements made by a silk-worm in the formation of a cocoon--Cowper’s beautiful lines on the silk-worm--Periods in which its various progressions are effected in different climates--Effects of sudden transitions from heat to cold--The worm’s appetite sharpened by increased temperature--Shortens its existence--Various experiments in artificial heating--Modes of artificial heating--Singular estimate of Count Dandolo--Astonishing increase of the worm--Its brief existence in the moth state--Formation of silk--The silken filament formed in the worm before its expulsion--Erroneous opinions entertained by writers on this subject--The silk-worm’s Will.