An instrument shelter (Figure 4) is employed to screen off the direct and reflected sunshine, and to keep the thermometers dry. This shelter is a box with louvered sides, constructed in such form that there is a free circulation of air through it. It should be exposed in an open space as far away from buildings as may be convenient, or on a housetop, and be as free from shadows as possible. If such position cannot be secured, then place it on the north side of a building. [Illustration: FIG. 6.—Dry and Wet Bulb Thermometers.] =Comparison of Centigrade and Fahrenheit.= Only Fahrenheit and Centigrade are in general use. Figure 5 is designed to enable observers to convert temperature readings from one scale to the other without resorting to a mathematical formula. For precise reductions the following rules apply: To convert Fahrenheit to Centigrade: Subtract 32 and multiply by five ninths. To convert Centigrade to Fahrenheit: Multiply by nine fifths and add 32. =Humidity Affects Health and Complexion.= The importance to health of maintaining a proper humidity in living quarters during the winter months and during all months in the arid and semi-arid regions of the West is not fully appreciated. Each habitation should be supplied with one to several hygrometers (Fig. 6), and frequent readings should be taken of the dry and the wet bulb thermometers so as to be familiar with the conditions under which one is living. RELATIVE HUMIDITY TABLES Temperature Readings in Degrees Fahrenheit. Relative Humidity Readings in Per Cent. Barometric Pressure 29.0 inches.