64 



DISCOVERY 



The colour of the spot was held by Lowell to indicate 

 that " in such places we look down into the fiery, 

 chaotic turmoil incessantly going on " — a view held 

 also by Denning. Some authorities maintain, however, 

 that nothing but cloud is visible — that we cannot 

 even glimpse the true Jovian surface ; on the other 

 hand, Barnard has recently expressed the view that the 

 surface we see is not exactly a cloud surface. " The 

 appearance is more that of a pasty nature." 



Recent research has undoubtedly emphasised the 

 analogy between Jupiter and the Sun. Lau, in his 

 theory of Jupiter, suggested that the rapid rotation of 

 the planet is the explanation of the existence of con- 

 tinuous belts in place of isolated spot-groups such as 

 are seen on the slowly-rotating Sun. That the red 

 spot is akin to sun-spots has been recognised for many 

 years. As long ago as 1879, the Russian astronomer 

 Bredikhine noticed a group of objects resembling the 

 solar faculs encircling the spot. Phillips inclines to 

 the view that " the red spot is a vortex — analogous to 

 a cyclone on the Earth, though its prolonged existence 

 shows that it must be of great strength and probably 

 deep seated below the planet's visible surface." " We 

 might indeed expect many vortices to occur along 

 the lines of contact between viscous currents possessing 

 diverse velocities, and if many of the Jovian spots are 

 of this character, we have another analogy between 

 Jupiter and the Sun." Amid considerable diversity 

 of opinion regarding the finer detail on the disc of 

 Jupiter, it may be said that the work of the last two 

 generations has abundantly confirmed the view that 

 Jupiter, in common with the other giant planets, is in 

 a state of primeval chaos. As Barnard remarks — 

 " They are the worlds of the future. Perhaps millions 

 of years hence they will be discussing the possibility 

 of fife on the Earth — if they ever know of its existence — 

 or whether life ever existed there." 



All that is known of Saturn, Uranus, and Neptune 

 abundantly confirms this view. The belts of Saturn 

 are fainter and less conspicuous than those of Jupiter, 

 solely because of the much greater distance at which 

 that planet revolves. Doubtless, the relative scarcity 

 of spots is due to the same cause. It was not until 

 1794 that the appearance of a Saturnian spot gave the 

 clue to the period of rotation. In that year Herschel 

 perceived one, and from its motion fixed the length 

 of the planet's " day " at 10 hours 16 minutes. This 

 period was more or less confirmed by Hall at Washing- 

 ton in 1876, and later by Denning and Stanley Williams. 

 A bright spot noticed by Barnard at the Yerkes 

 Observatory in 1903 indicated a considerably longer 

 period, 10 hours 39 minutes, a fact which demonstrates 

 that Saturn, like Jupiter, does not rotate as a whole. 



Saturn resembles Jupiter not only in the broad 

 general features of its disc, but in the more intricate 



detail as well. Highly significant was the discovery 

 by Lowell of " wisps " similar to the wisps of Jupiter 

 — " filamentous streaks between the belts, sometimes 

 vertical but more often inclined, after the manner of 

 the lacings of a sail. Individually they resemble 

 distant droppings of rain from a storm cloud seen 

 slanting against the sky under the force of a strong 

 wind. At first they were described only across the 

 light equatorial zone, but have since been seen meshing 

 the whole surface of the disc." 



From the Lowell Observatory came in 1912 the 

 announcement of the successful measurement of the 

 rotation-period of Uranus. Perrotin and Thollon at 

 Nice in 1S84 believed that they had evidence of 

 rotation in about ten hours, but little confidence was 

 reposed in their result because of the extreme faintness 

 of the Uranian markings. Accordingly, to Dr. Lowell 

 and his assistant. Dr. V. M. Slipher — now director of 

 the Lowell Observatory — belongs the honour of ascer- 

 taining the period. The problem was attacked 

 spectroscopically by means of Doppler's principle, 

 and the planet was found to rotate on its axis in a 

 period of 10 hours 45 minutes in a retrograde direction. 



Dusky shadings — presumably belts — have been 

 glimpsed from time to time on the sea-green disc of 

 Uranus. They were glimpsed by Young at Princeton, 

 New Jersey, in 1883, and were distinctly visible to 

 the French astronomers, the brothers Henrj', at Paris 

 in 1S84. The detection of markings on Neptune is 

 due to the distinguished American astronomer. Dr. T. 

 J. J. See. On October 10, 1899, he noticed some belts 

 on the disc very faint and indistinct. Telescopic 

 observation indicates that Uranus and Neptune are 

 physically similar to the two larger planets. To the 

 spectroscope, however, we owe the greater part of our 

 knowledge of the two outermost worlds of the Solar 

 System. In 1902 Dr. Slipher began his investiga- 

 tion, of the spectra of the four giant planets at Flag- 

 staff. His photographs showed that the spectra of 

 Uranus and Neptune are much more complex than 

 those of Jupiter and Saturn, and indicated the exist- 

 ence of elements unknown or unidentified upon the 

 Earth. The atmospheres of the two outermost planets 

 would appear to be very extensive. In the case of 

 Uranus, Lowell reached the conclusion that in that 

 planet "we see a body in an early amorphous state, 

 before the solid, the liquid, and the gaseous conditions 

 of matter have become differentiate and settled each 

 into distinctive place. Without even an embryo core 

 its substance passes from viscosity to cloud." 



The giant planets differ from the dwarf in the 

 possession of important and genuine systems of satel- 

 lites. The Earth-Moon and the Martian systems both 

 appear to be somewhat sporadic cases, out of the regular 

 course of evolution. The genesis of the Moon, as Sir 



