Now as the hunters have begun watching hurricane centers close by on the radar, they see them changing shape and wiggling around. In fact, as stated in a few cases in earlier chapters, they have seen false eyes and have been confused by them until the true eye came into view on the radar scope. If the true eye describes a wiggly path and changes size, the hunters can draw the wrong conclusions about its direction of motion unless they wait a while to see if it comes back to the old path. The hurricane is a little like an eddy or whirl in water running out of the bottom of a bowl. It is a violent boiling eddy that twists and changes shape, and in a substance as thin as the atmosphere these motions are not steady to such a degree that the observer can reach a quick decision. At any rate, it is now apparent that the observers on ships and aircraft did not make as many errors as was thought several years ago. There is another aspect that must be kept in mind. Radar shows areas where rain is falling around the center of a hurricane and so the center, having no rain, stands out as an open space on the radar scope. This is very good if the storm has rain all around the center, but some of them have very little rain on the southwest side, and in some cases there is none to return an echo to the radar. In such a case, there is only one side to the storm echo and the location of the center is not revealed. Of course, these facts are known to the experienced radar men, but they should be known to everybody interested in hurricane reports; otherwise they are likely to expect too much accuracy from observations of this kind. For these and other reasons, the man on the aircraft has a very great advantage in daylight, for he can see clouds of all kinds, measure the winds and, by moving through the storm area at the speed of the modern plane, he can see a large part of it in a short time. To find a substitute for aircraft reconnaissance is going to be extremely difficult. But at night the situation is quite different. The airman is unable to see much without radar, except on a moonlight night and that is not very good. One suggestion that has been put forward by a number of different people in recent years is that a balloon be flown in the calm center and followed by radar or radio, thus keeping track of the storm’s motion. It is possible, of course, to fix a small rubber balloon (perhaps eight to ten feet in diameter) so that it will remain at the same height for a fairly long time. By one method the rubber balloon is partly filled with helium and covered loosely with nylon. The balloon expands as it rises, becoming less dense as the atmosphere gets thinner. It continues to rise until it fills the nylon cover and cannot expand further. After that, its density becomes the same as the air at some level previously chosen, and from there it drifts along without rising or descending.