302 



DISCOVERY 



a trace. Can this be the true explanation of 

 Epiphanius' reference to Peponza : " The Montanists 

 honour a deserted place in Phrygia, formerly a city 

 called Pepouza, but now levelled with the ground, and 

 they assert that the New Jerusalem descends there " ? 

 The heretic Aetius, we know, was banished to Pepouza 

 (if that is the correct form of " Petonsa " which we read 

 in the text of Philostorgius) in a.d. 356, and it has been 

 argued that this disproves the statement of Epiphanius. 

 But may we not rather enjoy the grim humour dis- 

 played in the choice of a place of exile ? The interest- 

 ing detail recorded by Eusebius, that the Christians of 

 the Phrygian town died " calling upon the God who is 

 over all," is to be explained by reference to the pro- 

 phecy of Joel, quoted in Acts ii. 17-21, " And it shall 

 be in the last days . . . blood and fire and vapour of 

 smoke . . . and it shall be, that whosoever shall call on 

 the name of the Lord shall be saved." Such a reference 

 suits the Montanists, whose faith was founded on the 

 literalness of the prophecy in the Apocalypse, which 

 foretold that a Great Persecution would precede the 

 Second Advent. Neither Eusebius nor Epiphanius 

 had any sympathy either with Montanism or with 

 scientific history ; between the lines of their narratives 

 I am inclined to read the fate which befel the New 

 Jerusalem of the Montanists in the Great Persecution. 

 Can a similar faith and a similar prejudice be in- 

 voked to explain why the Christain martyrs who are 

 gradually being restored to History by the inscriptions 

 of eastern Phrygia are unknown to the Calendar of 

 the Church ? 



Among the Stars 



A Monthly Commentary 



The Giant Planets : A New Theory of their 

 Constitution 



As is well known even to those who have only a superficial 

 knowledge of astronomy, the primary planets of the 

 Solar System — exclusive of the asteroids — are divided 

 into two groups which differ widely from each other. 

 The four inner or dwarf planets are small, dense, mature 

 bodies, while the four outer or giant planets are of great 

 volume but comparatively small density. For the last 

 half-century, indeed since Zollner and Proctor showed 

 that the clouds on Jupiter were in all probability raised 

 by the intense internal heat of the planet, the opinion 

 has prevailed that Jupiter, Saturn, l^ranus, and Neptune 

 are great inflated masses, partly gaseous, with very high 

 internal temperatures. Despite much that is obscure and 

 mysterious in regard to the giant planets, this view has 

 been widely accepted, and has been on the whole satis- 

 factory in explaining the markings both on Jupiter and 

 Saturn. In a recent paper, however, Dr. Harold Jeffreys, 



who has made a special study of problems of cosmogony, 

 challenges the prevailing theory and puts forward an 

 alternative hypothesis. " The data," he states, " are 

 more easily reconcilable with the hypothesis that these 

 planets are cold and solid, their material being of low 

 density in comparison with terrestrial rocks." 



Dr. Jeffreys agrees with most astronomers in main- 

 taining that in the case of each of the four outer planets, 

 what we see is not the surface of a solid globe. This is 

 proved by the fact that these planets do not rotate as 

 rigid bodies ; the rotation period is dependent on the 

 latitude. What we actually observe is a cloud layer in 

 the atmosphere at a height corresponding to that of 

 terrestrial cumulus and strato-cumulus clouds. Nor does 

 Dr. Jeffreys deny that the densities of the outer planets 

 are very low. He joins issue with the accepted explana- 

 tion of these facts — namely, that the planets are largely 

 gaseous and intensely hot. " The low density affords 

 as good an argument for the hypothesis that these planets 

 are solid as against it. It compels ns, however, to 

 suppose that these planets are all composed of matter 

 verv diftcrcnt from the chief constituents of the Earth." 



TilE ri.ANET S.\TURN AND ITS RINGS. 



Here Dr. Jeffreys invokes the tidal theory of the origin 

 of the Solar System, suggested by Dr. Jeans and developed 

 by himself. On this theory the giant planets would keep 

 most of their lighter material, while the dwarf planets 

 would only retain their heavier matter. Accordingly, 

 Dr. Jeffreys maintains that the giant planets are com- 

 posed of something less dense than terrestrial rocks, and 

 he finds confirmation of this in the low density of the 

 satellites of Jupiter and Saturn. " The high albedo of 

 Saturn's ring suggests that it is composed of some colour- 

 less substance in a state of fine division, possibly ice or 

 some other light non-metallic compound. 



Dr. Jeffreys agrees that the atmospheres are \-ery 

 extensive, the depth being one-fifth of the radii of the 

 planets. These atmospheres must be cold, and the sus- 

 pended clouds in them " are probably composed of some 

 material with much lower boiling and melting points 

 than water." The hypothesis is a revolutionary one, and 

 will probably meet with considerable opposition. It will 

 undoubtedly have the effect of quickening interest in the 

 giant planets and their nature. 



The Nature of the Spiral Nebulae 



Professor Lindemann's hypothesis of the nature of 



