Februaky 1, 1868.] 



♦ KNOWLEDGE 



noted in Mercury's case to only 30 miles. Our earth has a 

 domain about 3l'2,S00 miles in diameter, and the maximum 

 sun-imparted velocity of bodies entering that domain is 26 

 miles per second. As the span of the moon's orbit is neai-lj- 

 478,000 miles, the moon is not within the earth's domain, 

 nay, lies 77,500 miles beyond the range within which the 

 earth's rule is supreme, so that the moon is to be regarded 

 as a companion planet rather than as a mere satellite. 

 Mars is the only member of the sun's special family of 

 planets — for so I think we must consider the terrestrial 

 planets to be — which has dependent bodies under its own 

 special influence. For the domain of Mars is nearly 

 165,000 miles in diameter, while his satellites travel at dis- 

 tances of only 5,820 miles and 14, GOO miles, respectively, 

 from his centre. At the distance of Mars the greatest 

 velocities of passing bodies, so far at least as solar influence 

 is concerned, amount to 21 miles per second, and Mars can 

 do little to perturb bodies moving so quickly, even though 

 their course should carry them through the very midst of 

 his domain. 



So soon, however, as wo pass to the wide region within 

 which lie the paths of the giant planets, we find planetary 

 domains far wider in extent and wherein planetary in- 

 fluences are exerted under conditions much more favourable. 

 The domain of Jupiter has a diameter of nearly 30,000,000 

 miles, within which the whole system of the Jovian satel- 

 lites, the span of which is but 2,800,000 miles, is swayed by 

 the planet's supreme influence, slightly modified by the 

 sun's perturbing action, indeed, but only in the same sense 

 in which the motion of the earth around the sun is modified 

 by the perturbing action of Jupiter. The domain of Saturn 

 is even larger, but so slightly that one may speak of the 

 domains of Jupiter and Saturn as practically equal. (Their 

 actual diameters are, respectively, 2t), 824, 000 miles and 

 20,912,000 miles.) And though the Saturnian system of 

 satellites has nearly twice the span of the Jovian system, 

 the diameter of the orbit of his eighth .satellite being no less 

 than 4,500,000 miles, yet this system is as completely under 

 Saturn's control as the motions of the terrestrial planets are 

 under the control of the central sun. Matter which has 

 entered within these two nearly equal domains travels with 

 sun-imparted velocities ranging up to eleven and one-half 

 miles jier second in the case of Jupiter and to eight and 

 one-half miles per second in the case of Saturn. Over matter 

 so moving both Jupiter and Saturn may exert very consider- 

 able influence, modifying not only the direction of motion, but 

 also — which is a point of much greater moment — its 

 velocity, and so modifying the span and period of orbital 

 motion which such matter may have had around the sun. 

 It is to be noticed that not only is the domain wide in each 

 case within which either Jupiter or Saturn exerts superior 

 influence, but the comparativeU' slow motion of sun- 

 influenced matter through that domain causes the matter 

 which has entered it from without to be much longer sub- 

 jected to disturbing influence than it would be if it rushed 

 along there with the velocities of 21, 26, 31, or 42 miles per 

 second with which matter crosses the domains of Mars, the 

 Earth, Venus, and Mercury. In this respect Uraniis, with 

 a smaller domain than either Saturn or Jupiter, and weaker 

 influence within that domain, has an advantage over both 

 those chief giants of the solar system. For the greatest 

 velocity (sun-imparted) with which matter can pass through 

 the domain of Uranus falls short of 6 miles per second. 

 The span of the domain of I'ranus is not far short of 

 24,00(1,000 mUes, and the system of Uranian satellites, the 

 span of which is about 1,000,000 miles, lies well within the 

 limits of the Uranian domain. But Neptune is, of all the 

 members of the solar system, the one whose domain is 

 widest, and whose influence within his domain is most 



strikingly pai'amount. This domain has a diameter of more 

 than 40,000,000 miles, and in volume it is nearly equal to 

 all the other planetary domains put together. Matter 

 passes through this domain when entering it by chance from 

 without under solar influence only, with velocities which 

 range no higher than 4| miles per second ; and as 

 Neptune is so powerful that matter drawn to his .surface 

 under his own influence alone would have a velocity of 

 impact amounting to 13f miles per second, it is evident 

 that Neptune must be capable of perturbing the movements 

 of such matter in very large degree. 



Such are the relations of matter as we find it distributed 

 within our solar system. A total quantity of matter sur- 

 passing even the tremendous mass of the eai'th no less than 

 331,000 times appears in this system aggregated into various 

 discrete masses, nearly all, however, being at the centre, 

 whence it may not only influence but warm and illuminate 

 all the rest. We see the various masses, according to their 

 amount and position, exercising sway over larger or smaller 

 regions of space, and over more or less important subordinate 

 .systems. We note, further, the antecedent probability — 

 and the evidence obtained by observation assures us of the 

 actual fact — that the larger these several masses are, the 

 more they retain of the heat due to the primary process of 

 their aggregation, the more nearly do they resemble the chief 

 mass in their power to warm — possibly in their power to 

 illuminate also — the bodies circling around them. 



If these details of our solar system were not, though I 

 think thev are, most interesting in them s si ves, they would 

 be made supremely interesting by the comideration that each 

 one of the stars tells us of an aggregation of matter re- 

 sembling our solar system doubtless in origin, though the 

 circumstances of their formation may have led to difl'erent 

 details alike of distribution and condition. Here in our 

 solar system certain processes acting according to the known 

 law of universal gravitation, and also according to those 

 physical laws on which the generation of the so-called 

 physical forces depends have led to the gathering together 

 of an enormous central mass with the generation and 

 steady emission of immense quantities of light and heat. 

 Yonder in space we see in each star evidence of the 

 steady emission of immense quantities of light and heat, 

 assuring us of the past aggregation of immense quantities of 

 matter. Our solar .system is the one case we can actually 

 study of the aggregation of matter under laws not yet 

 clearly recognised, and still farther from being fully inter- 

 preted. It may perhaps be in one sense as hopeless to 

 endeavour to guess how other such aggregations have been 

 formed as it is to endeavour to ascertain from our earth's 

 life history the life histories of her fellow-worlds, or from 

 the condition of our moon the state of all such orbs as have, 

 like her, passed onward to the final stage of orb life, the 

 condition of death. But even as from the laws of the life 

 of any one animal we ain form a general idea of the laws 

 of the lives of other animals, and as the study of one plant 

 afibrds data for the determination of the general laws of 

 plant life, so we may fairly infer the general nature of the 

 final stage of orb life from the condition of our moon, the 

 general laws of world life from the life history of our earth 

 (so far as we have been able to read it), and lastly the 

 general nature of other sun-circling systems from the study 

 of the distribution of matter within our solar system, and 

 the state in which the matter so distributed exists, whether 

 in the supreme central mass, in the larger or smaller among 

 the subordinate masses, or in the relatively minute sub- 

 divisions of the original material of the system which wo 

 recognise in asteroids and satellites, in meteorites, aerolites, 

 and finally in the particles of mere cosmical du.st whoso 

 presence is attested by the phenomena of falling stars. 



