Deduce a general rule for the circulation and velocity of the wind in a cyclonic area, as shown on your tracing, and write it out. _B._ =Anticyclones.=——This exercise is done in precisely the same way as the preceding one, except that anticyclones and their winds are studied instead of cyclones. Deduce a general rule for the circulation and velocity of the wind in an anticyclonic area, as shown on your tracing, and write it out. =The control of the wind circulation by areas of low and high pressure= is one of the most important laws in meteorology. Buys-Ballot, a Dutch meteorologist, first called attention to the importance of this law in Europe, and it has ever since been known by his name. Buys-Ballot’s Law is generally stated as follows: _Stand with your back to the wind, and the barometer will be lower on your left hand than on your right._[4] This statement, as will be seen, covers both cyclonic and anticyclonic systems. The circulations shown on your tracings hold everywhere in the Northern Hemisphere, not only around the areas of low and high pressure seen on the United States weather maps, but around those which are found in Europe and Asia, and over the oceans as well. Mention has already been made, in the chapter on isobars (VII), of the occurrence of immense cyclonic and anticyclonic areas, covering the greater portion of a continent or an ocean, and lasting for months at a time. These great cyclones and anticyclones have the same systems of winds around them that the smaller areas, with similar characteristics, have on our weather maps. A further extension of what has just been learned will show that if in any region there comes a change from low pressure to high pressure, or _vice versa_, the system of winds in that region will also change. Many such changes of pressures and winds actually occur in different parts of the world, and are of great importance in controlling the climate. The best-known and the most-marked of all these changes occurs in the case of India. During the winter, an anticyclonic area of high pressure is central over the continent of Asia. The winds blow out from it on all sides, thus causing general northeasterly winds over the greater portion of India. These winds are prevailingly dry and clear, and the weather during the time they blow is fine. India then has its dry season. As the summer comes on, the pressure over Asia changes, becoming low; a cyclonic area replaces the winter anticyclone, and inflowing winds take the place of the outflowing ones of the winter. The summer winds cross India from a general southwesterly direction, come from over the ocean, and are moist and rainy. India then has its rainy season. These seasonal winds are known as _Monsoons_, a name derived from the Arabic and meaning _seasonal_. [Footnote 4: In the Northern Hemisphere.] [Illustration: FIG. 48.]