rods, since the same account applies to them all.
We must first describe the phenomena and the circumstances in which each of them occurs. The halo often appears as a complete circle: it is seen round the sun and the moon and bright stars, by night as well as by day,Chris Terry Tröjor, and at midday or in the afternoon,John Carlson Tröjor, more rarely about sunrise or sunset.
The rainbow never forms a full circle,Tyson Jost Tröjor, nor any segment greater than a semicircle. At sunset and sunrise the circle is smallest and the segment largest: as the sun rises higher the circle is larger and the segment smaller. After the autumn equinox in the shorter days it is seen at every hour of the day,Dan Hamhuis Tröjor, in the summer not about midday. There are never more than two rainbows at one time. Each of them is three-coloured; the colours are the same in both and their number is the same, but in the outer rainbow they are fainter and their position is reversed. In the inner rainbow the first and largest band is red; in the outer rainbow the band that is nearest to this one and smallest is of the same colour: the other bands correspond on the same principle. These are almost the only colours which painters cannot manufacture: for there are colours which they create by mixing,Buty Jordan Retro 10, but no mixing will give red, green, or purple. These are the colours of the rainbow,Vince Dunn Tröjor, though between the red and the green an orange colour is often seen.
Mock suns and rods are always seen by the side of the sun, not above or below it nor in the opposite quarter of the sky. They are not seen at night but always in the neighbourhood of the sun,Ralph Lauren byxor, either as it is rising or setting but more commonly towards sunset. They have scarcely ever appeared when the sun was on the meridian,PJS Herreklær Harraseeket Parkas, though this once happened in Bosporus where two mock suns rose with the sun and followed it all through the day till sunset.
These are the facts about each of these phenomena: the cause of them all is the same,Dino Ciccarelli Tröjor, for they are all reflections. But they are different varieties, and are distinguished by the surface from which and the way in which the reflection to the sun or some other bright object takes place.
The rainbow is seen by day,Jakub Voracek Tröjor, and it was formerly thought that it never appeared by night as a moon rainbow. This opinion was due to the rarity of the occurrence: it was not observed, for though it does happen it does so rarely. The reason is that the colours are not so easy to see in the dark and that many other conditions must coincide,Guy Lafleur Tröjor, and all that in a single day in the month. For if there is to be one it must be at full moon, and then as the moon is either rising or setting. So we have only met with two instances of a moon rainbow in more than fifty years.
We must accept from the theory of optics the fact that sight is reflected from air and any object with a smooth surface just as it is from water; also that in some mirrors the forms of things are reflected,Jack Eichel Tröjor, in others only their colours. Of the latter kind are those mirrors which are so small as to be indivisible for sense. It is impossible that the figure of a thing should be reflected i
相关的主题文章：
http://cgi.tako.ne.jp/~friends/bbs3/light.cgi?res=13734
http://www.matsue-yado.com/otoku/clip.cgi
http://www13.plala.or.jp/gakuki3/cgi_bin/aska/aska.cgi |
