Prepare a piece of tracing paper by drawing an N. and S. line upon it, and placing a dot at the center of the line. Lay the paper over an area of low pressure on any weather map, centering and orienting it properly, as in the previous exercises. Trace off the isotherms which are near the center of low pressure. Repeat this process with several maps, selecting different ones from those used in the first part of this exercise. Formulate a rule for the observed distribution of temperature, and determine the reasons for this distribution. Note carefully any effects of the cyclone upon the temperature gradient. _B._ =Anticyclones.=——The correlation of anticyclones with their temperatures is studied in precisely the same way as the preceding correlation. Both methods suggested in the case of cyclones should be used in the case of anticyclones. When your results have been obtained, formulate a general rule for the observed distribution of temperature in anticyclones, and determine the reasons for this distribution. Find from your composites the average temperature of cyclones and of anticyclones, and compare these averages. =The unsymmetrical distribution of temperature around cyclones=, which is made clear by the foregoing exercises, is very characteristic of these storms in our latitudes, and especially in the eastern United States. That this has an important effect upon weather changes is evident, and will be further noted in the chapter on _Weather Forecasting_. The cyclones which begin over the oceans near the equator at certain seasons, and thence travel to higher latitudes,——_tropical cyclones_, so called,——differ markedly from our cyclones in respect to the distribution of temperature around them. The temperatures on all sides of tropical cyclones are usually remarkably uniform, the isotherms coinciding fairly closely with the isobars. The reason for this is to be found in the remarkable uniformity of the temperature and humidity conditions over the surrounding ocean surface, from which the inflowing winds come. In the case of our own cyclones, in the eastern United States, the warm southerly wind, or sirocco, in front of the center has very different characteristics from those of the cold northwesterly wind, or _cold wave_, in the rear, as has become evident through the preceding exercise. These winds, therefore, naturally show their effects in the distribution of the temperatures in different parts of the cyclonic area. CHAPTER XV. CORRELATION OF THE DIRECTION OF THE WIND AND THE WEATHER.