8 



KNOWLEDGE. 



[January, 1904. 



predominaut law of force. Professor Darwin's paper thus 

 stands out as a monument of in«,'enious niathematieal 

 treatinieint applied to an ideal state of things. 



An aggregation of revolving meteorites has no figure of 

 eqailihrium ; and it is through the consequences neces- 

 sarilv resulting from this property that mathematicians 

 are enabled to trace the progressive changes of a rotating 

 fluid mass. In the absence of any such direct means of 

 attack, their position regarding the problem presented by 

 an assemblage of flying stones is not much better than that 

 occupied by Kant, face to face with an evolving universe. 

 It seems, however, clear that a meteor-swarm can condense 

 only through the effects of collisions among its con- 

 stituents. When the irregularities of movement upon 

 which their occurrence depends are got rid of, the 

 system must remain in statu quo. Order makes for 

 permanence ; a tumultuary condition is transient. The 

 eventual state of the system can, however, be no 

 more than partially foreseen. Bodies arrested in their 

 flight should fall inward ; hence a central mass would 

 form and grow ; but the production of planets would 

 seem to be conditional upon the existence of primitive 

 inequalities of density in the swarm. These might serve 

 as nuclei of attraction for meteoric infalls, not yet com- 

 pletely exhausted, but plying with harmless fire one at 

 least of the globes they helped to shape. There could, 

 indeed, on this showing, have been no such harmonious 

 succession of events as constituted the predominant chanu 

 of Laplace's scheme. The planets should be supposed to 

 have issued pell-mell out of a chaos ; or, rather, the chaos 

 should have contained frona the beginning the seeds of a 

 predestined cosmos. Its evolution would have been like 

 that of the oak from the acorn, an unfolding of what was 

 already essentially there. And it may be that at this stage 

 of penetration into the past, the unaided human intellect 

 meets its ne plug ultra. There is a vital heart of things 

 which we cannot hope to reach. Thought instinctively 

 pauses before the vision of the symbolical brooding 

 Dove. 



To resume. Meteoric cosmogony deserves serious con- 

 sideration. Materials for the purpose probably exist 

 abundantly ; and, in the solar system at least, they must 

 have been formerly much more abundant than they now 

 are. The earth has been raking up meteoric granules 

 by hundreds of millions daily during untold ages, and her 

 zone of space is still very far from being swept clean. The 

 persistence of the supply, however, may be occasioned by 

 the continual aiTival of reinforcements from interstellar 

 realms. Comets appertain to, and travel with the sun's 

 cortege ; and this is also inevitably true of comet-born 

 meteors. But a multitude besides circulate independently 

 of comets, and with much higher velocities. Their orbits 

 are then hyperbolic ; they belong to the ca,tegory of 

 " irrevocable travellers," and their capture provides us 

 with genuine samples of sidereal matter. Universal space 

 must contain them in vast numbers, yet there is nothing 

 to prove their collection into swarms. The spectroscope 

 supplies no assm-ance to that effect ; it has given its verdict 

 against the meteoric constitution of nebulse and temporary 

 stars. And if we admit, under the compulsion of minera- 

 logical testimony, that the aerolites so strangely landed on 

 terrestrial soil are really the drbria of ruined worlds, we 

 can see for them no chance of restoration. Solitary they 

 are, even if they occasionally pursue one another along an 

 identical track, and solitary they must remain. Bodies do 

 not of themselves initiate mutual circulation. Planetary 

 or stellar outcasts cannot become re-associated into a 

 gravitational system. Of a cosmic swarm, as of a poet, it 

 may be said, Nascitur, non jit ; and their birth-secret is 

 undivulged. 



JUPITER AND HIS SURFACE CURRENTS. 



By the Eev. T. E. E. Phillips, m.a., f.e.a.s. 



The general aspect in the telescope of the planet Jupiter 

 is well known. His markedly elliptical disc, which is 

 distinctly brighter in the centre and gradually fades off 

 towards the limb, is traversed by a series of dusky belts 

 which vary from time to time both in width and position. 

 These Ijelts frequently show great irregularities at the 

 edges, being broken up or indented by a number of light 

 and dark spots, while dusky wisps are often to be seen 

 projecting from them across the bright zones which 

 separate them. The accompanying drawings will serve to 

 illustrate the general arrangement of the surface features 

 and also the great and rapid changes of aspect to which 

 they are subject. Thus it will be seen from the illustra- 

 tions that in" the years 1896 and 1898 (Figs. 1 and 3)— as 

 was also the case in 1901 and 1903 — the belt lying North 

 of the equator was quite narrow, b>it that at other times 

 it was broad, and exhibited numerous condensations and 

 white spots at its edges. It not infrequently happens that 

 the general aspect of the planet undergoes a marked 

 alteration even in the coiu-se of a single apparition. 

 Thus Fig. (> represents a view of Jupiter in June, 1902, 

 but l>y the latter part of the autumn the appearance of 

 the disc had materially changed. The equatorial regions 

 were intensely white — a very striking contrast to the rich 

 warm coppery tone which was so marked a feature of the 

 planet a few years ago — and the whole of the disc North 

 of the N. temperate belt was deeply shaded with a delicate 

 bluish grey. 



It is probable that some of the changes on Jupiter are 

 of a cyclical or seasonal character. Mr. A. Stanley 

 Williams in a valuable paper communicated to the Eoyal 

 Astronomical Society in April, 1899, showed from a 

 discussion of a large number of observations extending 

 over many years that there is a remarkable variation in 

 the colour of the two principal equatorial belts. Thus, 

 when the S. equatorial belt is at a maximum of redness, 

 the N. equatorial belt is at a minimum, or even bluish in 

 tone, and vice versa. The mean period of these variations 

 is found to be about twelve years, and as this corresponds 

 \vith the length of a sidereal revolution of Jupiter round 

 the sun, it is probable that the change observed is of a 

 seasonal character. The maximum redness occurs soon 

 after the vernal equinox of the particular hemisphere in 

 which the belt exhibiting it is situated. In accordance 

 with the interesting conclusion at which Mr. Williams 

 has arrived, the N. equatorial belt has lately been in- 

 tenselv red, and the S. equatorial belt almost colourless, 

 except in the region immediately following the Eed Spot 

 bay. 



JBut, perhaps, the most interesting and instructive 

 feature hitherto observed in connection with Jupiter is 

 the difference of speed with which his spots and other 

 markings are drifting. So long ago as the latter part of 

 the 17th centuri-, Cassini found that the markings in the 

 neighbourhood of the equator performed a rotation in 

 nearlv six minutes less time than was required by objects 

 further north and south. Sir William Herschel, Schroter, 

 and other observers confirmed this result, but as the 

 outcome of the labours of more modem investigators, a 

 considerable number of distinct currents are now known 

 to control the movements of Jupiter's surface material. 

 There can be no doubt that many recorded changes on 

 Jupiter are in reality due to the great proper motions of 

 the objects observed, which quickly cause them to become 

 relatively displaced. 



