356 



KNOWLEDGE 



[Dec. 14, 1883. 



very great terror of aggressive man, though they are 

 gradually getting less and less tame as time goes on. Even 

 in England, the big birds are much more cautious than the 

 small ones ; and perhaps the very wariest of all is the 

 heron, which has been hunted and hawked after in former 

 times more persistently, in all probability, than any other 

 of our native birds. The ;;reat bustard, now practically 

 extinct in Britain, but still found on the continent of 

 Europe, is even more preternaturally suspicious of man, the 

 bustard-stalker, than the heron himself. On the other 

 hand, sea-birds which breed on isolated rocks, and so have 

 little opportunity for forming an acquaintance with the 

 ways of humanity, like penguins and boobies, are often so 

 tame that they can be readily caught with the hand or 

 knocked over by dozens with a sailor's knob-stick. 



The instinct of fear is thus very gradually acquired, and 

 only by dint of much bitter ancestral experience : but when 

 once gained, it is comparatively easily lost, and may even 

 be replaced by affection and confidence after a very short 

 acquaintance, not in captivity only (where the bird has no 

 option), but in the native condition. Sparrows, which, as 

 the most town-haunting of all birds, have had especial 

 opportunities of learning the fickleness and treachery of 

 man (still generally in the form of boy), do not so readily 

 make friends with us as do robins ; but in Paris, where the 

 habit of taking a stray shot at every small bird is far less 

 common than in London, everybody must have noticed 

 how familiarly even these street Arabs of the winged 

 world will perch upon the shoulders of the benevolent 

 old gentlemen who feed them daily in the Tuileries 

 gardens. In cold weather, starlings and thrushes are also 

 very easily conciliated : and the far timider woodland birds 

 themselves can be tamed by some few exceptional people 

 who have the faculty of inspiring animals with a sort of 

 intuitive confidence. I have often tamed mice myself by 

 ottering them crumbs at judiciously graduated distances, 

 till at last they would come upon the dinner table to be fed, 

 a habit which appeared to cause more fear to the ladies 

 present than to the little visitors themselves. In Jamaica 

 the turkey-buzzards, or local vultures, which are protected 

 by law as useful scavengers, have learnt their immunity so 

 well, and become so bold upon the strength of it, 

 that they will even sometimes fly into the houses, 

 whence they are only ejected by some display of 

 physical force on the part of the rightful owners. I 

 once saw three turkey-buzzards devouring a dead dog by 

 the roadside ; and La order to test their freedom from fear I 

 tried to drive them off from the carrion with my walking- 

 stick. The experiment was so eminently successful in 

 proving their fearlessness that at the end of one moment it 

 was the experimenter himself who was beating a hasty 

 retreat in the direction of the nearest negro cottage, 

 pursued by three exasperated and threatening vultures, 

 who seemed disposed seriously to resent so unwarrantable 

 an infringement on their ancient legal rights and pri- 

 vileges. 



s 



THE ZONE OF SMALL PLANETS. 



By Eichaed A. Pboctor. 



{Confiiiued from page 320.) 

 O soon as we consider the theory of the solar system's 



origin to which all the known facts point, we find — 

 as it appears to me — an explanation of all those features of 

 the ring of asteroids which had seemed most perplexing or 

 (it is nearly the same thing) most significant. 



The known facts are these — 



First, the singular distribution of the masses forming the 



system. Secondly, the departures from uniformity, as in 

 the various inclinations of orbits, and of the rotational 

 movements of the planets. Thirdly, more marked de- 

 partures from uniformity on the outskirts of the system, 

 seen in the reversed movements of the satellites of Uranus 

 and Neptune, and probably in reversed rotations of these 

 outer planets. Fourtldy, the existence of millions of 

 meteoric systems, moving in all directions and at all dis- 

 tances from the sun, on paths having every variety of 

 inclination and of eccentricity. Fifthly, the marked resem- 

 blances between the systems of Jupiter and Saturn on the one 

 hand and the Sun's special family of small planets (Mercury, 

 Venus, Earth and lluon, and Mars) on the other. Sixthly, 

 the gaps in the mean distances of the asteroids. Seventhly, 

 and for our present purpose lastly, the gaps in the 

 Saturuiau ring-system, which like the zone of asteroids 

 consists of multitude.s of small bodies. 



As I showed thirteen years ago in my " Other Worlds 

 than Ours," all the first four features of the solar system 

 correspond with the theory that each member of the system 

 was in large part formed (Laplace's nebular hypothesis 

 need by no means be absolutely abandoned) by meteoric 

 aggregation. Withoxit this theory those features are abso- 

 lutely inexplicable. And as, even now, though at a greatly 

 reduced rate, the process of meteoric ingathering goes on, 

 our earth yearly gathering in an enormous absolute mass 

 of matter in this way, however small that mass may be 

 compared with the earth's, we know that the theory is a 

 true one — though in what degree the formation of the various 

 members of the solar system is to be explained in this way, 

 may of course be open to question. 



With regard to the fifth feature, I know nothing more 

 suggestive of the meteoric stream theory of the formation 

 of the solar system than this. Anyone who has watched 

 some mighty eddying, whirling stream, and has seen how 

 perfectly the minor eddies in such a stream present in 

 miniature the features of the greater whorl of which they 

 form part, will see how strongly the resemblance between 

 (for instance) the system of Jupiter and the central part of 

 the solar system — the sun's special family as I have learned 

 to regard it — suggests the idea of a minor eddy in a mighty 

 whirlpool, like the minor whorls in the great whirlpool 

 nebula itself. 



But now be it noted that the sixth feature, the charac- 

 teristic gaps in the asteroidal system — a strange and 

 altogether perplexing feature without this theory — is pre- 

 cisely what we should expect to find in any case where 

 meteoric aggregation led to the formation of a ring of small 

 bodies instead of a separate planetary mass. [I would 

 ask the reader before proceeding, here, to study the illus- 

 trative picture of the asteroidal family, supposed to be 

 distributed in circular orbits at their proper mean distances 

 (see p. 291, No. 106) : he will recognise, I think, the force 

 of the evidence, and see how the objection raised by 

 Professor Newcomb on the strength of two or three 

 asteroidal orbits near one of the gaps disappears when 

 graphic evidence replaces mere statistical investigatioiL] 



Every member of a meteoric stream moving in a period 

 which synchronised (in a simple way) with the movements 

 of Jupitei''s giant mass would undergo at each return to 

 conjunction with Jupiter the same kind of perturbation. 

 This renewal of perturbation acting in the same direction 

 would result in an accumulated disturbance, aflecting the 

 mean distance. We see this on a grander scale in the case 

 of Saturn, whose period nearly synchronises with Jupiter's 

 in such sort that five periods of the Giant Planet are 

 nearly equal to two periods of the Ringed Planet : hence 

 results what is called the Great Inequality. Now apart 

 from other causes of disturbance, the eflect in the case of 



