Our inventions increase in geometrical ratio. They are like living beings, each one of which may become parent of a dozen others--some good and some ne'er-do-weels; but they differ from animals and vegetables inasmuch as they not only increase in a geometrical ratio, but the period of their gestation decreases in geometrical ratio also. Take this matter of Alpine roads for example. For how many millions of years was there no approach to a road over the St. Gothard, save the untutored watercourses of the Ticino and the Reuss, and the track of the bouquetin or the chamois? For how many more ages after this was there not a mere shepherd's or huntsman's path by the river-side--without so much as a log thrown over so as to form a rude bridge? No one would probably have ever thought of making a bridge out of his own unaided imagination, more than any monkey that we know of has done so. But an avalanche or a flood once swept a pine into position and left it there; on this a genius, who was doubtless thought to be doing something very infamous, ventured to make use of it. Another time a pine was found nearly across the stream, but not quite; and not quite, again, in the place where it was wanted. A second genius, to the horror of his fellow-tribesmen--who declared that this time the world really would come to an end--shifted the pine a few feet so as to bring it across the stream and into the place where it was wanted. This man was the inventor of bridges--his family repudiated him, and he came to a bad end. From this to cutting down the pine and bringing it from some distance is an easy step. To avoid detail, let us come to the old Roman horse-road over the Alps. The time between the shepherd's path and the Roman road is probably short in comparison with that between the mere chamois track and the first thing that can be called a path of men. From the Roman we go on to the mediaeval road with more frequent stone bridges, and from the mediaeval to the Napoleonic carriage-road. The close of the last century and the first quarter of this present one was the great era for the making of carriage-roads. Fifty years have hardly passed, and here we are already in the age of tunnelling and railroads. The first period, from the chamois track to the foot road, was one of millions of years; the second, from the first foot road to the Roman military way, was one of many thousands; the third, from the Roman to the mediaeval, was perhaps a thousand; from the mediaeval to the Napoleonic, five hundred; from the Napoleonic to the railroad, fifty. What will come next we know not, but it should come within twenty years, and will probably have something to do with electricity.