Dec. 21, 1883.] 



♦ KNOWLEDGE ♦ 



369 



^ AN ILyiSIRATED \> 



MAGKlNEoFSSIENCE 



\ FLAINLTjfORDED -£XACTL^^E SCRIB£D 



LONDON: FRIDAY, DEC. 21, 1883. 



Contents of No. 112. 



The Universe of Suns. By Eichard 



A. Proctor 369 



Ladybirds. By E. A. Butler, B.A. 370 

 Caverns in Earth and Moon. By 



Eichard A. Proctor 371 



Evidences of the Glacial Period . . 373 

 €lieap and Good Food. By T. K. 



AlEnson, L.E.C.P 374 



Kecreation Through Uncertainty. 



By Sir James Paget 375 



PAOB 



The Amateur Electrician (.lUiu.) ... 375 

 Sun Views of the Earth. By E. A. 



Proctor 377 



Science and Safety at Sea. By E. 



A. Proctor 378 



Editorial Gossip 379 



The Face of the Sky. By F.E.A.S. 379 

 Correspondence : A Blue Moon — 



Strange Sunsets— Coincidences ... 380 

 Our Chess Column 382 



THE UNIVERSE OF SUNS. 



By Richard A. Proctor 



ALTHOUGH we are placed at present iu a far more 

 advantageou.s position for forming an opinion respect- 

 ing the con.stitution of the heavens, than any of those who 

 have in former ages inquired into this subject, yet we 

 cannot att'ord to neglect any of the hints thrown out by 

 men like Galileo and Huyghens, Wright, Kant, Lambert, 

 and Michell. Moreover the account of former hypotheses 

 respecting the universe is full of interest. 



The ideas of ancient astronomers respecting the stars 

 were naturally very far from the truth. Anaximenes 

 regarded the stars as studs on the crystalline sphere, 

 while Theophrastus supposed that the celestial sphere 

 consists of two distinct halves fastened together along the 

 Milky Way, but so imperfectly that we can see through 

 the unclosed spaces the luminous heavens beyond. Xeno- 

 phanes taught that the stars are clouds collected in the 

 u|)per regions of the air, and fed from the fiery lether. 

 Itence the remark of Callimachus that the circumpolar 

 stars feed on air ; and hence the question of Lucretius, 

 " Unde (vthcr aidera pascit ?" Anaxagoras considered that 

 the stars, as well as the sun, moon, and planets, were rocks 

 swept oti' from the earth by the a>ther, and kindled to an 

 intense heat in the fiery upper regions. 



Passing, however, from these vague fancies, let us turn 

 to those hypotheses which were formed when the Coper- 

 nican theory enabled men to form some conception of the 

 <-normous distances of the fixed stars, and when telescopic 

 researches began to reveal vast numbers of stars hitherto 

 unseen by man. 



Copernicus himself occupied a somewhat exceptional 

 (losition, since he was the only astronomer wlio ever 

 •tiieorised respecting the stars on the liasis of the system 

 which bears his name, but without the knowledge re.spect- 

 ing unseen stars which his successors ol)tainod by means 

 of the telescope. It should be noticed also in considering 

 the views of (Joperniciis, that thouj^h he had abandoned the 

 Ptolemaic astronomy, he had by no means abandoned the 

 artificial conceptions on which Ptolemaic astronomy had 

 been based. That this is so, can be recognised even in the 

 account which Co|)erniciis gave of the motions within the 

 .solar system : it is still more :ipp:ir('nt in his rcmaiks re- 



specting the universe. " It is to be observed in the first 

 place," he says, in his treatise " De Revolutionibus," " that 

 the universe is spherical ; not only because that is the most 

 perfect of all figures, needing no fastening or junction, com- 

 ]>lete in itself; but because it is the most capacious figure, 

 fittest to enclose and preserve all things ; because the most 

 perfect portions of the universe, — the sun, moon, and 

 stars, — are seen to have that sha])e ; and lastly because, as 

 we see in drops of water and other liquids, all things capable 

 of assuming the figure they prefer, select the figure of a 

 sphere." Of the sphere of st:irs, however, he remarks only, 

 that it is the outermost and chief of all the spheres, im- 

 movable because enclosing all other spheres. 



Galileo, the first Copemican to recognise the enormous 

 extent of the stellar regions to which the unaided eye cannot 

 penetrate, formed no theory respecting the universe. He 

 saw clearly, however, the extreme importance of those 

 revelations made by the telescope, and their bearing on the 

 theories men had formed respecting the Galaxy. " It is 

 truly a wonderful fact," he said, "that to the vast number 

 of fixed stars which the eye perceives, an innumerable 

 multitude, before unseen, and exceeding more than tenfold 

 those hitherto known, have been rendered discernible. Nor 

 can it be regarded as a matter of small moment that all 

 disputes respecting the nature of the Milky Way have 

 been brought to a close, and the nature of this zone made 

 manifest not to the intellect only, but to the senses." 



Kepler was the first astronomer who enunciated definite 

 ideas respecting the constitution of the universe. In 1618, 

 or nine years after the jiublication of the two first of the 

 laws which bear his name, he published the first three 

 books of his "Epitome," the fourth in 1620,* a year after 

 his third law had been published in his Harmoniu Mundi. 

 The following statements have been extracted from the 

 " Epitome " by W. Struve, and form a fair abstract of the 

 ideas of Kepler : — 



The sun lies farther from the fixed stars than these lie 

 from each other. Within the sphere of the fixed stars 

 there is a vast concavity girt round on all sides by the stars. 

 The sun lies within this space, so that the solar system 

 occupies an exceptional position in the universe. The con- 

 cavity enclosing the snn lies also near the centre of the 

 zone called the Milky Way. This is shown by the fact 

 that the Milky Way appears as a great circle on the 

 heavens, and sensibly of uniform brightness throughout. 

 The space occupied by the stars, limited on the inside by 

 the concavity enclosing the sun, is also limited on the out- 

 side, and thus forms tin immense spherical shell, outside of 

 which lies spao' f The sun is the chief body — the heart of 

 the universe, — whence flow light and heat ; he is also the 

 ruler of the planets and their satellites. The sphere of the 

 fixed stars is as the skin of the universe preventing the 

 escape of the solar heat and reflecting the solar light. It ia 

 therefore as of ice, by comparison with the fiery ma-ss of 

 the sun. The stars according to this hypothesis are much 

 smaller than the sun, but shine with their own light, the 

 light of each having its own proper colour. | 



* Xot 1G22, though tlio titlc-pago bears that date. 



t Kepler bases this conclusion on the same reasons which 

 Copernicus had already alleged. 



X He admits, however, that the sun may possibly be only a star, 

 brighter because nearer than the rest ; and that the other stara 

 may be surrounded, like our sun, with planetary schemes. " This, 

 however," he remarks, " is not a necessary inference from the 

 Coperniean system, which decides nothing respecting the nature of 

 the tixed stare. We are therefore free to admit that the li.\ed stars 

 are spread, as tho Uebrow tradition asserts, within a sti-atum com- 

 paratively thin and of a watery nature, and that this stratum is 

 ervstalliue, the water in it being fi\>zeu on account of its great 

 distaiu-e from the sun, the centre of the heat of the universe." 



