In 1944 the Navy installed seismographs and began keeping records of the slight tremors caused by hurricanes and typhoons. These studies have shown that a tropical storm at a distance produces a small tremor which becomes stronger as the storm center gets nearer. No one knows exactly how the storm shakes the earth and causes the tremors. There are some strange things about this. It seems that these microseisms are carried along in the earth until they come to the border of a great geological block and then do not pass readily into the next block. So there are places in the Caribbean where the tremors weaken as they come to a different earth block and this interferes with the indications picked up by the instruments. The fact is that microseisms give signs of the existence of a tropical storm and sometimes serve to alert the storm hunters, but they are by no means good enough to replace the use of planes in tracking them. But the studies of microseisms are being continued. For many years static on the radio, better known as atmospherics or just “sferics,” has been used in the endeavor to locate or keep track of storms. At first the Navy tried it on West Indian hurricanes. The instruments used will find the direction from which the sferics come when they are received in a special tube. In more recent years, the Air Force has used this scheme. It works to advantage in finding thunderstorms, but tropical storms are so big and the sferics are not found in any regular pattern around the central region. After years of trial, it has been concluded that this scheme is not good enough to replace other methods. Of all the methods of this kind, radar is by far the best. But as the radar stations on shore and the radar equipment on aircraft have increased in numbers and have been improved to reach greater distances, some new troubles have arisen. For many years the hurricane hunters took it for granted that a hurricane has a clear-cut center which moves smoothly along a path that is a straight line or a broad curve, but in a few cases is a loop or a sharp turn. In other words, the center does not change size and shape or wiggle around. In the past, when an observer on a ship or on a plane reported a center of an odd shape or had it off the smooth path the hunters were plotting, they said the observer had made an error.