It would appear that the field of labour and the number of labourers, chiefly those who toiled with brick and mortar, were greatly reduced when those huge fireplaces were so widely discarded. This must have seemed so especially in those regions where the houses were built up to meet the yearning wants of an outside chimney, but armies of men are engaged in civilised countries in making stoves and furnaces, where three-quarters of a century ago very few were so employed. As in every industrial art old things pass away, but the new things come in greater numbers, demand a greater number of workers, develop new wants, new fields of labour, and the new and increasing supply of consumers refuse to be satisfied with old contrivances. In the United States alone there are between four and five hundred stove and furnace foundries, in which about ten thousand people are employed, and more than three million stoves and furnaces produced annually, which require nearly a million tons of iron to make, and the value of which is estimated as at least $100,000,000. The matter of _ventilation_ is such a material part of heating that it cannot escape attention. There can be no successful heating without a circulation of air currents, and fortunately for man in his house no good fire can be had without an outflow of heat and an inflow of cooler air. The more this circulation is prevented the worse the fire and the ventilation. It seems to many such a simple thing, this change of air--only to keep open the window a little--to have a fireplace, and convenient door. And yet some of the brightest intellects of the century have been engaged in devising means to accomplish the result, and all are not yet agreed as to which is the best way.