The whole relationship between earthquakes and the seasons in the northern and southern hemispheres is summed up in Fig. 12 taken from Knott. The northern hemisphere shows a regular diminution in earthquake frequency from December until June, and an increase the rest of the year. In the southern hemisphere the course of events is the same so far as summer and winter are concerned, for August with its maximum comes in winter, while February with its minimum comes in summer. In the southern hemisphere the winter month of greatest seismic activity has over 100 per cent more earthquakes than the summer month of least activity. In the northern hemisphere this difference is about 80 per cent, but this smaller figure occurs partly because the northern data include certain interesting and significant regions like Japan and China where the usual conditions are reversed.[131] If equatorial regions were included in Fig. 12, they would give an almost straight line. The connection between earthquakes and the seasons is so strong that almost no students of seismology question it, although they do not agree as to its cause. A meteorological hypothesis seems to be the only logical explanation.[132] Wherever sufficient data are available, earthquakes appear to be most numerous when climatic conditions cause the earth's surface to be most heavily loaded or to change its load most rapidly. The main factor in the loading is apparently atmospheric pressure. This acts in two ways. First, when the continents become cold in winter the pressure increases. On an average the air at sea level presses upon the earth's surface at the rate of 14.7 pounds per square inch, or over a ton per square foot, and only a little short of thirty million tons per square mile. An average difference of one inch between the atmospheric pressure of summer and winter over ten million square miles of the continent of Asia, for example, means that the continent's load in winter is about ten million million tons heavier than in summer. Second, the changes in atmospheric pressure due to the passage of storms are relatively sharp and sudden. Hence they are probably more effective than the variations in the load from season to season. This is suggested by the rapidity with which the terrestrial response seems to follow the supposed solar cause of earthquakes. It is also suggested by the fact that violent storms are frequently followed by violent earthquakes. "Earthquake weather," as Dr. Schlesinger suggests, is a common phrase in the typhoon region of Japan, China, and the East Indies. During tropical hurricanes a change of pressure amounting to half an inch in two hours is common. On September 22, 1885, at False Point Lighthouse on the Bay of Bengal, the barometer fell about an inch in six hours, then nearly an inch and a half in not much over two hours, and finally rose fully two inches inside of two hours. A drop of two inches in barometric pressure