In our winter months the contrasts of temperature in the United States are, as a rule, violent, there being great differences between the cold of the Northwest and the mild air of Florida and the Gulf States. In the summer, on the other hand, the distribution of temperature is relatively equable, the isotherms being, as a rule, far apart. In summer, therefore, we approach the conditions characteristic of the Torrid Zone. These are uniformly high temperatures over large areas. The same thing, on a larger scale, is seen over the whole Northern Hemisphere. During our winter months the isotherms are a good deal closer together than they are during the summer, or, in more technical language, the temperature gradient between the equator and the North Pole is steeper in winter than in summer. CHAPTER VI. WINDS. The observational work already done, whether non-instrumental or instrumental, has shown that there is a close relation between the _direction of the wind_ at any station and the _temperature_ at that station. Our second step in weather-map drawing is concerned with the winds on the same series of maps which we have thus far been studying from the point of view of temperature alone. In the second column of the table in Chapter VIII are given the wind directions and the wind velocities (in miles per hour) recorded at the Weather Bureau stations at 7 A.M., on the first day of the series. Enter on a blank weather map, at each station for which a wind observation is given in the table, a small arrow flying _with_ the wind, _i.e._, pointing in the direction _towards_ which the wind is blowing. Make the lengths of the wind arrows roughly proportionate to the velocity of the wind, the winds of higher velocities being distinguished by longer arrows, and those of lower velocities by shorter arrows. The letters _Lt._ (= light) in the table denote wind velocities of 5 miles, or less, per hour. When you have finished drawing these arrows, you will have before you a picture of the wind directions and velocities all over the United States at the time of the morning observation on this day. (See solid arrows in Fig. 26.) The wind arrows on your map show the wind directions at only a few scattered points as compared with the vast extent of the United States. We must remember that the whole lower portion of the atmosphere is moving, and not merely the winds at these scattered stations. It will help you to get a clearer picture of this actual movement of the atmosphere as a whole, if you draw some additional wind arrows between the stations of observation, but in sympathy with the observed wind directions given in the table and already entered on your map. These new arrows may be drawn in broken lines, and may be curved to accord in direction with the surrounding wind arrows. Heavier or longer lines may be used to indicate faster winds. (See broken arrows, Fig. 26.)