What would the Egyptians, who paid their tribute in glass to Rome, have thought of a serious order to pave the Via Sacra with blocks of purple glass? Yet such an order could be executed now at St.-Gobain, and when one sees the great flags weighing nine kilogrammes made here and used to let light into the cellarage below the carriage-ways, for example, of the huge Hotel Continental, at Paris, it comes easily within the probabilities that the whole underworld of our great cities in time may thus come to be made available for divers uses, as so much of the underworld of Broadway now is in New York. The great 'pavement question' is an open question still, in spite of asphalte and of wood, and there would seem to be nothing in the nature of things to prevent its being eventually solved by the glassworkers. The roofing question clearly belongs to them. The casting of glass for roofs began, I believe, with England, in the time of Sir Joseph Paxton, but it has been immensely developed at St.-Gobain. Over a hundred thousand square metres of glass roofing made here were required for the building of the Exposition of this year at Paris. All the most important railway stations in France, from Nantes to Strasburg (unless the Germans have changed this), and from Calais to Marseilles, are thus roofed. In great warehouses, markets, public museums, street galleries--like those of Victor Emmanuel at Milan--factories, workshops all over France and the Continent, this conversion of the roof into a colossal window has revolutionised matters within the last twenty years. The light is making its way even into Turkey, where the great bazaar at Salonica has been roofed in glass by St.-Gobain, and as the Chinese, who, despite their early invention of glass, never got beyond using it for beads and little bottles, have condescended to admit great French mirrors into the Imperial Palace at Pekin, the glass roof may, ere long, make its way even into China. In the form of tiles, such as are now made here, glass must inevitably, sooner or later, displace slates and shingles and terra-cotta for the roofs, even of private houses, it being quite certain that these glass tiles can be so used as to give a much better light in the garrets of private houses than can possibly be got through the windows. When that comes to pass the burglar's occupation of clambering stealthily from roof to roof will be seriously interfered with. What with glass roofs and glass floors and electricity, indeed, the city of the future is likely to be much more easily 'policed' and patrolled, as well as incomparably more cheery and habitable, than the city of to-day. Perhaps, too, when we all come to living in glass houses, the cause of peace and good neighbourhood may gain, and even Mrs. Grundy may grow more careful about looking into the affairs of her friends and acquaintances.