Reports of the U. S. Weather Department show that the relative humidity of Death Valley, which is the driest and hottest known country, during the driest period of the year--between May and September--averages 15.5 per cent. saturation. In winter, many buildings, particularly offices and school buildings are not far from that atmospheric condition, constantly. Under the usual conditions of house heating, there is an almost absolute lack of means to give moisture to the air. Almost without exception steam-heating plants and hot-water heating plants in office buildings and dwellings are without any provision for changing the atmospheric humidity. In school buildings that are not kept under a more desirable condition of temperature and humidity, the general health is impaired and the behavior of the pupils very markedly influenced. The tension of a school-room full of fidgety nervous children can be very promptly and greatly reduced by the introduction of water vapor into the air to 50 per cent. saturation. All modern school buildings, auditoriums, etc., are provided--aside from the heating plants--with means of ventilating in which the entering air is washed and humidified to the desired degree, before being sent into the rooms. The popular conception of the hot-air furnace method of heating is that it produces particularly dry air, when in reality it is the only type of house-heating plant in which any provision is made for adding water to the air. These furnaces are usually furnished with a water reservoir by use of which the humidity may be raised to a desirable point. Much of the water which enters the air of the average home, during winter weather, comes from the evaporation that goes on in the kitchen. Usually on wash days the humidity is raised to a marked degree and that day is commonly followed by a short period of agreeable atmospheric condition. The arrangement of many houses is such that a much-improved condition of humidity might be obtained from the kitchen by continuous evaporation of water from a tea-kettle. RELATIVE HUMIDITY Depression of wet-bulb thermometer (_t_-_t'_) --------------+----+----+----+----+----+----+----+----+----+---- Air temp. _t_ | 1.0| 2.0| 3.0| 4.0| 5.0| 6.0| 7.0| 8.0| 9.0|10.0 --------------+----+----+----+----+----+----+----+----+----+---- 35 | 91 | 82 | 73 | 64 | 55 | 46 | 37 | 29 | 20 | 12 36 | 91 | 82 | 73 | 65 | 56 | 48 | 39 | 31 | 23 | 14 37 | 91 | 83 | 74 | 66 | 58 | 49 | 41 | 33 | 25 | 17 38 | 91 | 83 | 75 | 67 | 59 | 51 | 43 | 35 | 27 | 19 39 | 92 | 84 | 76 | 68 | 60 | 52 | 44 | 37 | 29 | 21