114 



SCIENTIFIC NEVS^S; 



[Feb. 3, 1888. 



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ROYAL INSTITUTION. 

 The Great Planets. 

 In his fourth lecture Sir R. Ball informed his hearers that 

 the stars which could be seen were only a small part of 

 the universe. One of the grandest conceptions of 

 astronomy was that all the stars we could see were only 

 one group, one cluster. There was no more beautiful 

 object than the Milky Way. Through a telescope it was 

 seen to be composed of myriads of minute stars, looking 

 minute because of their immense distance; and our sun 

 was but one of the vast host of stars therein comprised. 

 Therefore the Milky Way consisted of stars separated by 

 the most appalling distances from each other. From 

 some parts of the universe it could not be distinguished 

 as other than a little cluster of stars in the sky. Coming 

 to the subject of the planets, the lecturer remarked that 

 between Mars and Jupiter there was a multitude of little 

 planets only a few miles in diameter, and not visible 

 except through a large telescope. On one of these little 

 planets gravity would be so shght that an inhabitant, 

 falling, would come down as gently as if lying down on 

 a feather-bed. The vastness of the craters in the moon 

 was accounted for by the diminished gravity as compared 

 with that of the earth, the effect of a volcanic explosion 

 being to throw the matter a much greater distance than 

 would be the case upon the earth. With the same effort 

 required here to lift fifty-six pounds or to throw a ball a 

 hundred yards, a man on the moon would lift six times 

 as much, or throw a ball six hundred yards. On the 

 larger planets a fall would be more serious, and weight 

 would be much greater than on the earth. Jupiter, the 

 largest planet of the solar system, more than a thousand 

 times the size of the earth, appeared through the telescope 

 as a vast globe, marked all over with cloudy bands. It 

 seldom looked alike for long together, as it revolved on 

 its axis in nine hours. There were no traces of solid 

 continents or oceans, only a stupendous mass of cloud ; 

 and it was very doubtful if our telescopes had ever yet 

 enabled us to see the solid interior. The moons were 

 much larger than the earth's satellite ; and it was by ob- 

 servation of the rays of light falling from those satellites 

 that the theory of the aberration of light was discovered. 

 Jupiter was not perfectly round, but bulged as it were in 

 the centre, no doubt owing to its rapid revolution on its 

 axis. This was illustrated by experiments with a revol- 

 ving chain loop and rotating springs. Passing to Saturn, 

 Sir Robert Ball described it as the most beautiful object 

 in the heavens, and exhibited a model of it, as well as a 

 number of pictures showing the progress made in ob- 

 serving the planet from ancient times. Saturn travelled 

 round the sun in a very wide orbit, occupying about 

 thirtj' years, and was very much larger than the earth. 

 Up to about one hundred years ago Saturn was the 

 farthest planet from the sun which had been discovered, 

 only five being then known. 



The Comets. 

 In the fifth lecture the Astronomer Royal of Ireland 

 dealt with the great and small comets. Having illustrated 

 the elliptical nature of their course, he explained how, as 

 they neared the sun, their volume, under the influence 

 of its intense heat, expanded, and the tail was produced 



and developed, while their rate of progression was aug- 

 mented until they travelled many hundreds of miles per 

 second. Illustrating this by a light, hollow ball of iron, 

 he showed how in its progress it attained a speed sufficient 

 to insure its continuing on its course, notwithstanding 

 the attraction of a powerful magnet which, however, was 

 strong enough to deflect it from the line it would other- 

 wise have pursued, and compel it to describe a parabola. 

 As it receded from the centre of attraction the comet's 

 speed gradually diminished, until at last it crawled along 

 " at a pace which any old omnibus would despise." The 

 commonest form of comet was that of which a specimen 

 was seen in 1843, which, after travelling on for 

 thousands of years, attained such an enormous speed as 

 it neared the sun that it passed round it in two 

 hours. The intense heat to which comets were ex- 

 posed as they approached the sun drove the gaseous 

 substance of which they were composed into smoke and 

 vapour, and thus was formed the tail, which was always 

 seen directed from the sun. Some of the more re- 

 markable comets were shown in illuminated transparencies 

 and the lecturer called special attention to Halley's comet, 

 which came round every seventy-five years, its next 

 appearance being due in 19 10. The movements of this 

 comet had been followed for nearly 2,000 years, and the 

 great comet recorded to have been seen before the birth 

 of Christ, and again in 1066, when a drawing was made 

 of it which was reproduced in the Bayeux tapestries, 

 had been shown to be that which we knew as Halley's. 

 As to the direful predictions that were sometimes made 

 of what would happen if the earth ever came into collision 

 with a comet, the lecturer explained that these eccentric 

 visitors were composed of merely gaseous or possibly 

 semi-liquid material, and that the largest of them would 

 not weigh more than a few tons. On Midsummer Night, 

 1 86 1, the earth actually did pass through the tail of a 

 great comet, and, with one solitary exception, nobody 

 noticed anything unusual, the only serious consequence 

 being that a certain country rector was compelled to 

 suspend his sermon until candles had been procured to 

 enable him to continue reading it. The relation between 

 a comet and the splendid display of shooting stars on 

 November 12th, 1866, was explained, and the lecturer 

 observed " that as this particular comet returned every 

 thirty-three years the same phenomena would be seen 

 on the i2th or 13th of November, 1899. Sir R. Ball 

 pointed out the insignificance of our sun in the scheme 

 of the universe, many of the stars which we saw at 

 enormous distances being really suns far brighter and 

 grander than that from which we derived light and heat. 

 The grandest truth in nature was that which expressed 

 that our sun was only one, and not a very important one 

 of some millions of suns which we saw twinkling 

 throughout the universe. Were it and its whole system 

 of earth and planets blotted out, all that would be noticed 

 from those further worlds would be that another little 

 star had ceased to twinkle. 



The Stars. 

 The last lecture of the course was upon the stars. The 

 question, " What is a star ? " was one which a child often 

 answered, but it was one to which a philosopher could 

 give but a partial reply. Our sun was, after all, only a 

 star, and all the other stars were suns. The difference 

 in apparent brightness between the sun and the stars 

 was due to the fact that we were close to the one and 

 a long way from the others. About 6,000 stars could be 



