At this period of moving, most people become familiar with the general appearance of dust, and the peculiarly disagreeable sensations produced by its getting into the eyes, nose, and y mouth. Few pause to consider what it is or where it comes from. We repeat the passage, " Dust thou art and to dust thou shalt return," but we hardly realize that the almost impalpable particles which exert their pungent power to compel us to sneeze, or cough, or make the tears to run down our cheeks, may be composed of the same matter that constituted the body of some ancestor a thousand years ago, and for whom we never felt called upon to weep until now. Our readers will recollect the significant query, " Who ate Roger Williams?" and how it originated in the discovery tliat the body, of that resolute controversalist had been appropriated to the growth of a greedy apple tree, which, not content with the theft, mimicked with its roots the body and limbs it had devoured. Of course the fruit produced on this tree, doubtless eaten with satisfaction, some of it perhaps by the iescendants of Roger Williams, contained the very matter which once was a living being; and the same matter may have been a million times exchanged and transported, so that the dust which is perhaps this moment provoking the reader to sneeze, may be a portion of that which once revolted against puritan persecution, and wended its way from the Colony of Massachusetts, to find a grave beneath a Rhode Island apple tree. Dust is commonly regarded as being matter of death. But though upon examination with a powerful microscope we find it to contain myriads of skeletons of dead organic beings, we shall also find that we are not roaming in a microscopic grave yard merely. We shall find the reproductive bodies of the diatoms, about which so much has been written and said by microscopists as to whether they were plants or animals, finally resulting in the belief that they are plants. Ehren-berg has described several hundred kinds of diatoms found in atmospheric dust. There are also to be found encysted ani- malculse and rotatoria, and their germs; spores or seeds of fungi, algae, lichens, and other cryptogamic or flowerless plants, intimately mingled with particles, consisting of cells and portions of cells, of both animal and vegetable tissues, and finely comminuted mineral substances. Among the latter,salts of sodium are some of the most generally diffused, although near bodies of salt water they are to be found in largest quantity, being carried into the air in the spray of oceanic waves, and afterward precipitated by the evaporation of the water which held them in solution. Silica, alumina, lime, and ox'de of iron, are always lound. Near manufacturing establishments there are always more or less of the materials used in the works to be found, as sulphur, oxide3 of the metals, and carbon deposited from smoke. In the vicinity of tanneries tannin may be found; and near dye-works, coloring matters. Dust is so universally diffused throughout the atmosphere that no place within the limits of animated existence can be said to be free from it under ordinary circumstances. To remove it even from small quantities of air requires quite complex mechanical and chemical manipulations. In regions subject to miasmatic diseases, organic matter is found in the greatest abundance in the form of spores. Its presence is determinable by a very simple test. Strong sulphuric acid has the property of freeing carbon from its combinations in organic substances. If a piece of wood be immersed in it it will be converted into charcoal. If then, a watchglass containing strong sulphuric acid, be exposed to the atmosphere the acid will after a time become blackened by the carbonization of the organic matter deposited upon its surface-It has been found that in malarial districts, sulphuric acid thus exposed becomes blackened much more readily than in other places, thus proving the presence of organic matter. In view of these facts it will be seen that streets filled with dust, must be prejudicial to the sanitary condition of large towns, and that the laying of this dust by sprinkling, is more than a mere matter of comfort to their inhabitants. Our readers have been informed of the method adopted last year in London, i. e., the use of solution? of deliquescent salts, to lay street dust, and of the success that attended the experiment. We have no doubt of the value of this method and urge its trial in the large cities of this country. The additional cost of te salts would probably be compensated for by the dimin" ished necessity for frequent application, and the increased health and comfort of the people, as well as the saving to merchants of the damage to their wares, frequently a serious matter along dusty thoroughfares.