_Smoky Chimneys._ When a chimney smokes, the draught is downward. This may be, caused—1. By an obstruction in the flue or stove-pipe. 2. By a higher chimney in the same house, the air coming down the shorter chimney, and going up the other. The remedy is to equalize the heights, or close the doors between the two. 3. If, when the fire is started, the air outside is warmer than that in the chimney, the heavier column will of course fall. This effect will vanish in a few minutes, when the flue becomes heated. 4. The doors and windows of the room may be so tight as to prevent a sufficient supply of fresh air to burn the fuel. If so, they must be opened. 5. The chimney may be lower than the adjoining wall, and the wind from certain directions, striking the wall, may be directed down the flues. This may be remedied by extending the chimney above the wall, or by capping the flues with one of the various cowls that prevent a downward draught. CHAPTER II. DRAINAGE. =How to prevent the contamination of the air by the products of decomposition.= There is no evidence to show that the emanations from fresh house-slops, or the excreta of healthy animals, are injurious to health, but it has been proved that when these matters decompose they become dangerous. The bubbles of gas which rise to the surface of such decomposing matters, when they burst, throw up solid particles of organic matter in the air, which float about for some time before falling to the ground. It is, therefore, essential to health that all such matters shall be removed from the vicinity of human beings promptly, before decomposition sets in, or else so manipulated as to prevent decomposition, or promote rapid oxidation. The lower animals seem to recognize by instinct that their excreta are dangerous, and they deposit them (except when penned up by men) in places remote from their abodes, or else carefully cover them with fresh earth. Man alone retains his excreta in carefully prepared receptacles near his place of residence, until the accumulation is so large that he is forced to remove it.