Wind Direction and Velocity.—Wind is an important meteorological element because it has many close relations to human life. It affects very markedly our bodily sensations of heat or cold. A cold, calm day is pleasanter than a cold, windy day. On the other hand, a hot, calm day is usually much more uncomfortable than a hot, windy day. High winds cause wrecks along seacoasts and damage houses, crops, and fruit trees. Sea breezes bring in fresh, cool, pure air from the ocean on hot summer days. In the tropics the sea breeze is so important in preserving the health of Europeans in many places that it is known as “the doctor.” The movement of wind through large cities carries off the foul air which has collected in the narrow streets and alleys, and is thus a great purifying agent.
Record the direction of the wind according to the four cardinal points of the compass (N., E., S., and W.) and the four intermediate points (NE., SE., SW., and NW.). The direction of the wind is the point from which the wind blows. You can determine the points of the compass roughly by noting where the sun rises and where it sets.
Note the velocity of the wind according to the following scale, proposed by Professor H. A. Hazen of the United States Weather Bureau.
| 0 | Calm. |
| 1 | Light; just moving the leaves of trees. |
| 2 | Moderate; moving branches. |
| 3 | Brisk; swaying branches; blowing up dust. |
| 4 | High; blowing up twigs from the ground, swaying whole trees. |
| 5 | Gale; breaking small branches, loosening bricks on chimneys. |
| 6 | Hurricane or tornado; destroying everything in its path. |
The record book will need two additional columns when wind observations are begun, as follows:—
Sample Record of Temperature and Wind.
| Date. | Hour. | Temperature. | Wind Direction. | Wind Velocity. | Remarks. |
| Oct. 3 | 7.30 A.M. | Cool | NE. | Moderate | Temperature falling since last evening. Wind velocity increasing. |
| “ | 11 A.M. | “ | “ | Brisk | Temperature the same. Wind velocity still increasing. |
| “ | 3 P.M. | “ | “ | High | Wind velocity still increasing. |
What is the direction of the wind to-day? What is its velocity? Has its direction or velocity changed since yesterday? If so, was the change sudden or gradual? Have you noticed any calms? What was the direction of the wind before the calm? What after the calm? Does there seem to be more wind from one compass point than from another? Is there any relation between the direction of the wind and its velocity? i.e., is the NW. wind, for instance, usually a brisk or a high wind, or, is the SE. or S. wind usually moderate? Does the wind usually change its direction gradually, as from SE. to S., then to SW., then to W., etc., or does it jump all at once, as from SE. to W.? Is there any relation between the velocity of the wind and the hour of the day, i.e., does the wind seem stronger or weaker at noon than in the morning or at night? Is it a common occurrence to have a wind from the same direction for several successive days, or are we apt to have different winds almost every day? Do you notice any systematic changes in wind direction which are
often repeated? What are these changes? Can you make a simple rule for them? In what ways does the wind affect us?
State of the Sky.—By the state of the sky is meant the condition of the sky as to its cloudiness. Clouds add much to the beauty and variety of nature. They are often gorgeously colored at sunset. By their changes in form, color, and amount from day to day they relieve what might otherwise be a wearisome succession of the same weather types. Prevailingly overcast skies have a depressing effect. Prevailingly clear skies become monotonous. A proper amount of bright sunshine is essential for the ripening of crops, but too much sunshine may parch soil and vegetation, and become injurious. Clouds bring rain; hence a sufficient amount of cloudiness is just as necessary as a sufficient amount of sunshine. The drift of clouds shows us the direction of movement of the air above us, and is of considerable help in forecasting the weather. Fog, which is a very low cloud, is in some cases so common as to be a meteorological element of great importance. In the city of London, where fogs are very prevalent, especially in winter, the average number of hours of bright sunshine in December and January is only fifteen in each month. The London fogs are, in great part, due to the presence in the air of vast numbers of particles of soot and smoke from millions of fires. These particles increase the density of the fog and prolong its duration.