_C._ =The Relation of Local Pressure Changes to Cyclones and Anticyclones, and thus to Weather Changes.=——Make a detailed study of the relation of the local pressure changes at your station, as shown by the barograph curves, or by frequent readings of the mercurial or aneroid barometers, to the passage of cyclones and anticyclones, and to their accompanying weather changes. Classify the simple types of pressure change, so far as possible, together with the general weather conditions that usually accompany these types. Apply the knowledge of local weather changes thus gained when you make your forecast on the basis of the daily weather maps. CHAPTER XXVI. METEOROLOGICAL TABLES. The tables which follow are those which are now in use by the United States Weather Bureau. They were first published in the _Instructions for Voluntary Observers_ issued in 1892, and were reprinted in 1897. The following instructions will be found of service in the use of the tables:—— TABLE I.——DEW-POINT. The figures in heavy type, arranged in vertical columns at each side of the page, are the _air temperatures_ in degrees Fahrenheit, as recorded by the dry-bulb thermometer. The figures in heavy type, running across the page, denote the _differences_, in degrees and tenths of degrees, _between the dry-bulb and wet-bulb readings_, or, technically, the _depression of the wet-bulb thermometer_. The figures in the vertical columns denote the _dew-points_. Make your observation of the wet and dry-bulb thermometers and note the difference between the two readings. Find, in the vertical columns of heavy type, the temperature corresponding to your dry-bulb reading, or the nearest temperature to that. Then look along the horizontal lines of figures in heavy type for the figure which corresponds exactly, or most nearly, with the difference between your wet and dry-bulb readings. Look down the vertical column under this latter figure until you reach the horizontal line corresponding to your dry-bulb reading. At this point the figures in the vertical column give the dew-point of the air at the time of your observation. _Example_: Air Temperature (dry bulb), 47°; Wet Bulb, 44°; Difference, 3°. On page 148 will be found the table containing both 47° (dry bulb) and 3° (depression of the dew-point). In the twenty-eighth line of this table and in the seventh column will be found the dew-point, viz., 41°. _Example_: Air Temperature, 61.5°; Wet Bulb, 55.5°; Difference, 6°.