In some cities, the evils of street dust are supplemented by the mischiefs of coal smoke, to an aggravated degree. Wherever soft coal is burned as the principal fuel, a black, fuliginous substance goes floating through the air, and soils every thing it touches. It penetrates into houses and public buildings, often intensified by their own interior use of the same generator of dirt, and covers the books of the library with its foul deposits. You may see, in the public libraries of some western cities, how this perpetual curse of coal smoke has penetrated the leaves of all the books, resisting all efforts to keep it out, and slowly but surely deteriorating both paper and bindings. Here, preventive measures are impossible, unless some device for consuming the coal smoke of chimneys and factories were made compulsory, or the evil somewhat mitigated by using a less dangerous fuel within the library. But, aside from these afflictions of dust, in its most aggravated form, every library and every room in any building is subject to its persistent visitations. Wherever carpets or rugs cover the floors, there dust has an assured abiding-place, and it is diffused throughout the apartment in impalpable clouds, at every sweeping of the floors. Hence it would be wise to adopt in public libraries a floor-covering like linoleum, or some substance other than woolen, which would be measurably free from dust, while soft enough to deaden the sound of feet upon the floors. Even with this preventive precaution, there will always be dust enough, and too much for comfort, or for the health of the books. Only a thorough dusting, carried on if possible daily, can prevent an accumulation of dust, at once deleterious to the durability of the books, and to the comfort both of librarians and readers. Dust is an insidious foe, stealing on its march silently and unobserved, yet, however impalpable in the atmosphere of a library, it will settle upon the tops of every shelf of books, it will penetrate their inner leaves, it will lodge upon the bindings, soiling books and readers, and constituting a perpetual annoyance.