What a difference in private life was made by the introduction of chimneys and glass windows, for glass, though known to antiquity, was not commonly applied to the openings that, as the etymology of the English word implies, let in the wind! By the fifteenth century the power of lenses to magnify and refract had been utilized, as mirrors, then as spectacles, to be followed two centuries later by telescopes and microscopes. Useful chemicals were now first applied to various manufacturing processes, such as the tinning of iron. The compass, with its weird power of pointing north, guided the mariner on uncharted seas. The obscure inventor of gunpowder revolutionized the art of war more than all the famous conquerors had done, and the polity of states more than any of the renowned legislators of antiquity. The equally obscure inventor of mechanical clocks--a great improvement on the {8} older sand-glasses, water-glasses, and candles--made possible a new precision and regularity of daily life, an untold economy of time and effort. [Sidenote: Printing] But all other inventions yield to that of printing, the glory of John Gutenberg of Mayence, one of those poor and in their own times obscure geniuses who carry out to fulfilment a great idea at much sacrifice to themselves. The demand for books had been on the increase for a long time, and every effort was made to reproduce them as rapidly and cheaply as possible by the hand of expert copyists, but the applications of this method produced slight result. The introduction of paper, in place of the older vellum or parchment, furnished one of the indispensable pre-requisites to the multiplication of cheap volumes. In the early fifteenth century, the art of the wood-cutter and engraver had advanced sufficiently to allow some books to be printed in this manner, _i.e._ from carved blocks. This was usually, or at first, done only with books in which a small amount of text went with a large amount of illustration. There are extant, for example, six editions of the _Biblia Pauperum_, stamped by this method. It was afterwards applied, chiefly in Holland, to a few other books for which there was a large demand, the Latin grammar of Donatus, for example, and a guide-book to Rome known as the _Mirabilia Urbis Romae_. But at best this method was extremely unsatisfactory; the blocks soon wore out, the text was blurred and difficult to read, the initial expense was large. The essential feature of Gutenberg's invention was therefore not, as the name implies, printing, or impression, but typography, or the use of type. The printer first had a letter cut in hard metal, this was called the punch; with it he stamped a mould known as the {9} matrix in which he was able to found a large number of exactly identical types of metal, usually of lead.