WHAT WE KNOW ABOUT THE SUN.

Waikato Times, Volume XXV, Issue 2077, 29 October 1885, Page 4

WHAT WE KNOW ABOUT THE SUN.

The appeal ance of a sun spot ia familiar to most people, yet there is hardly a more at liking object in the whole realm of astronomy. When viewed with a poweiful telescope, its appearance is indeed bciutiful— the daik black nucleus or central portion, surrounded by the penumbwi, which has something of the appearance of an interlaced and entangled mass of silver threads, but with a general tendency towards the centre of the spot, sometimes projecting in the centre, foiming promontories, islands, and capes of silveiy white in a dead black sea. The size ot the spots is enormous. Herschel observed oue fifty thousand miles in diameter, or moie than six times the diameter of the earth. Sometimes clusters of innumerable small ones are observed ; and it is seldom that the surface of the sun is entirely free trom them. The fiist important result that followed the observation of sun spots was the determination of the sun's period of rotation, which has been approximately fixed at twenty-seven and one third-da) a. But here a very curious fact meets our notice, which is this— that the rate of rotation of all portions of the sun's surface is not the same ; there seems to be some retaiding action at work, which acting on the equatorial regions, causes them to lag behind. The formation of a spot is a slow piocess, and has often been observed ; their disappearance, too, generally takes some time. They have, however, on one or two occasions, been observed to explode and absolutely disappear almost in a minute or two, which, when we consider their enormous size, is an astounding phenomenon. According to Faye's hypothesis, the spots are tormed of huge masses of vapour, which, ha\ ing been cooled and partly condensed in the upper regions of the sun's atmosphere, sink into the fiery sea, which goes by the name of the photo sphere, or lightgiving portion of the sun. The action may be compared to that of an immense snow flake, w Inch, falling into water, is gradually melted. We now come to another and not the least remarkable thing connected with the spots— their period of maximum and minimum. To Schwabe of Dessau we owe the discovery of th.s lemarkable law, which may be thus stated : The average number of spots on the sun's surface is maximum at intervals of about eleven yeais. Atter a peuodoi maximum, the average slowly decreases, till it teaches its minimum in five and a half years. It then as slowly increases again, till it reaches the next maximum period— thus continually and regularly fluctuating. Yauous attempts have been made to connect it with the periods of conjunctions of different planets ; but until more exact knowledge of the precise length of the ■sun hpot period is obtained, we cannot admit any such explanation. One thing is, however, ceitain, that the periods of sun spot maximum aie coincident with the peiiods of maximum magnetic disturbance on the eaith, and with the appearance of the aurora borealis. The next point that atti acts our attention is the phenomenon of the prominences of red tlames seen during a total eclipse. These lemarkable objects have lately been completely studied by means of the spectroscope. It has thus been found out that they consist of huge clouds of incandescent hydrogen, mixed in some cases with dilleient metallic vapours, and situated at some considerable height above the surface of the photosphere. Their movements aie sometimes extremely rapid, and they have been observed to appear or disappear in the course of a few minutes. On one occasion Profossor Young saw one of these prominences erupted to a height of two hun dred thousand miles in an hour or two. Prominences generally occur round a spot, or where a spot is going to bieak out. When seen on the body of the aun, they appear as facultc or bright spots. During a total eclipse, there is another sight which attracts the attention of the observer, and that is the corona, which appears in the form of a silvery white light for aome distance round the sun. Its outline is very ii regular, and though its appearance seems to remain substantially the same during the same eclipse, it vanes much from one eclipse to another. It was at first thought that this phenomenon might be due to refraction of our atmosphere ; but this was disproved, and it is now generally believed to be an emanation from the sun itself. The light given out by the corona is luckily that sort or light which has most effect on a sensitive photographic plate, and this fact early ga\ c rise to the hope that it might be possible to photograph the corona without the aid of an eclipse. This has, indeed been done by Dr Huggins, who had lately obtained photographs which, in the opinion of those best capable of forming a judgment, truly leprescnt the solar coiona. Photo graphy has given valuable assistance in the study of solar physics.

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An editor recently addressed to scvctal clergymen a query as to the rieshahlo length of seimonB. The replies, which weieduly published, cannot he said to settle this \ excel question. The Episco palian, who amongst others was asked "Do you believe in long sermons ? ' replied : " Short sermons, by all means, Less preaching, more praying, more woislup. ' Mine house shall be called a house of prayer,' never a house of preaching." The I'iesbyterian replied : •' That the average sermon of the average minister had better be thirty minutes long than forty. Seimons .should not be made to the yard stick, for all themes cannot be handled with the same brevity." The Methodist believed in long and short sermon 1 ?. The Baptist, in a lengthy reply, confessed that for many years he had made this same subject a matter of special study a.nd observation. He thus sums up the results of his experience : " As a iu!e, the less a man lias to say the longer he takes to do it. I am fully persuaded that, save in very exceptional instances, whatever else a sermon is about, if ought to be about half an-hour. I know men, otherwise gifted, who am failures in the nnnistiy, localise they hit the nail on the head at the first time, and then keep hammeiing till they split the board." Tlrese replies, if they establish anything, sbow that sermons should be weighed rather than measured.