The Study of “Siranui”

Abstract

Shiranui, which means literally an unknown fire, has been very famous from ancient times as a mysterious sea fire in Japan. It is usually said that on the Yatsushiro Sea (or the Shiranui Sea) in Kumamoto Prefecture, Kyushu, Japan, it appears most clearly at the time of lower low water on the night of the last day of the seventh month of the lunar calendar. It is also said that it is not seen from the sea, but only from heights of the coast of the Sea.
At first, only one luminous point appears, and then it splits out into a great many starlike twinkling fires in the length about 4 kilometers in the horizontal direction of the Sea. Such fires as just above mentioned are seen almost continuously from midnight to dawn. On that night, many people flock to the coast together from the neighbouring villages to see these misterious fires, Shiranui; but it can not be seen well unless when it is very fine.
Many investigators or explorers already tried to study “What Shiranui truely is.” But they were all in vain, for whenever they would try to draw near it going on board, it would suddenly disappear. Thus the true nature of Shiranui has remained unknown.
Now, there are various opinions about it. Some people are of the opinion that Shiranui is a fishing fire, and the others that it is due to the luminescence of microbions in the Sea. But there are not so many fishing fires as those of Shiranui, nor so bright luminescence of microbions as that of it either.
In last summer, we observed Shiranui with many co-workers by using large telescopes, a spectroscope and a falling camera, from a high place at Eino in Matusai, one of the towns in the coast of the Sea. Then we measured the temperatures of the sea water and of the air on the Sea. and also of the air on the beach of the vicinity where Shiranui would most frequently appear. The thermometers used by us were mercurial ones and thermographs.
From the results of these observations and measurements, it is concluded that the light sources of Shiranui are acetylene lamps used in fishing. The light emitted from a lamp scintillates, flying in the direction of the horizon, splitting out into many lights, when it passes through the discontinuous air mediums produced near the surface of the sea as shown in Fig. 2. This, indeed, is the true cause of the phenomenon of Shiranui.
Why these air mediums are formed discontinuously will be explained as follows. At a time of lower low water, many extremely wide beaches appear along the coast, which is, indeed, a characterestic of this vicinity. Now, the temperature of the air on the beaches is lower than that of the air on the sea at night. Thus when a breeze blows in the direction of light beams, the warmer air on the sea is mixed with the cooler one which comes from the beaches. Then it produces on the sea many discontinuous air layers, through which we can see Shiran_??_i. The phenomenon of Shiranui is very interest from the point of view of meteorolog'cal optics.