THE SUN.

Manawatu Times, Volume XXVI, Issue 7166, 18 February 1901, Page 4

THE SUN.

INTERESTING LECTURE BY SIR R. BALL.

The usual Christmas course of lectures, specially adapted to juveniles, was begun at the Royal Institute recently. The lecturer this year is Sir Robert Ball, and the title of the course " Great Chapters I from tho Book of Nature." tho lectures b^ing intended to illustrate the bearing of modern astronomical discovery on Laplace's famous doctrine of the evolution of the sun and planets. Sir Robert Ball devoted his opening I lecture to "The Sun and its Heat." The sun, he pointed out, was the source of all the heat received by the earth ; it might seem rather puzzling to find that the temperature grew colder as one climned to the top of a mountain, and tbns got nearer this source of heat, but the explanation was that the air acted as a sort of cosy, and the climber lost more warmth by going partially through it than he gained by approaching nearer the sun, In size the sun was in comparison with the earth as a good*sized cocoanut to a grain of mustard seep, and he poured forth his heat from every part of his surface. No one was so foolish as to suppose that all this heat was in-

tended only for this earth ; there was. indeed, enough of it to warm millions of worlds.like ours if they were properly disposed round the sun. It was a literal scientific fact that, as calculated by Professor Langley, all the coal in the world would not supply the sun's heat

for one-tenth of a second. Another I indication of the intensity of the heat he gave off was the fact that the rays collected by a large burning glass were able to melt the most refractory substances. In the Paris Exhibition a steam engine was shown at work driving a printing press by heat derived directly from the sun ; the boiler was placed in the focus of a big mirror, which by gathering together the hot beams,.boiled the water and produced the necessary

steam. This little apparatus was as yet

only a plaything, but it might come to be of vast importance. The spots to be seen on the surface of tho sun were rents in the brilliant external envelope which enabled tbe dark inteiior to be seen : they appeared to be moving across the disc, but the truth was that ihe sun

himself revolved in a period of about 25 days. Photography was able to reveal something of the structure ol the sun. The external envelope looked as if it wero of a granula texture, i_<ide up of little bits of wool, each of these little bits, however, was as large &a Great Britain at least. The brilliant' outside was a coating only—about as thick in proportion to the whole as the delicate skin of a peadh, What was the sun made of? What made the film of luminous clouds that floated over bim ? What gave the sua the power of being so bright and beautiful ? If it wero asked what was the most important discovery of the century now ending, there is no doubt that the reply should be, so far as the heavens were concerned, the discovery of the actual materials composing the heavenly bodies. To find this out would have been considered impossible a hundred years ago, since it was impossible to take a piece of the sun or of a sun into the labatory for analysis; now it was one of the famous truths of science. The sun was known to consist essentially of the same sub* stances as the earth. One of these was calcium, which, though in the metallic form it was very rare and precious, .was plentiful in the form of lime and of great importance to the inhabitants of this earth. Carbon, again, was another very rare substance on the earth, and it wa3 also a most . important element in the sun, for it was the Bubstance whose presence gave him the power of sending the light and heat enjoyed by the people of this earth. The carbon vapours welling up from the centre of the sun became a little cooled and were turned into little solid particles, each glowing with a brilliance like that of the electric light, tbe lamps for which were in fact made with carbon. We found out many things about the sun when there was a total solar eclipse, when the moon coming between the suu and the earth shut off tho direct light of the former from us. Then, the sun was seen to be girdled with huge rosy flames or prominences which wore ordinarily blotted out from our view by his own brilliance, though by a method invented by Lockyer and Jaunsen, it was possible to see them even when there was no actual eclipse. During a total eclipse, too, and then only, the pearly light of the corona was visibly encircling the sun's disc. The sun was continually in a state of fierce excitement and was always parting with his heat. Now, it wa3 a, well-known fact that most things in cooling became smaller; a poker, for example, was shorter when it was cold than when it was red hot. The sun, too, must obey this fundamental law, and must therefore be getting smaller. If we could measure its diameter on two successive days we should find it had decreased by nine inches—that was to say, it was shrinking at the rate of, roughly, five feet a week, or a mile in every 20 years. In view of this shrinkage, seme of the younger members of his audience might feel anxious lest the sun should not last their time. Such anxiety, however, was groundless ; ho was 560,000 miles in diameter, 36 it would take 40,000 years for him to be reduced by' 2000 miles tq 858,000, and the lecturer was sure that U there wore two suns in the sky, one 860,000 miles in diameter, and the other 858,000, no one would be able to tell by looking at them which of the two was the smaller. But as the sun was shrinking nine iuches every day, and had bean doing so for ageS, it followed tha* ill tho he was very much greater than he was now.! But he always had the same amount of material' in him and weighed no heavier than at present; hence" tho inference was that he was once a huge mass of rarefied gas—a great glowing nebula. The lecture was illustrated with many lantern slides.