Jan. 1, 1886.] 



♦ KNOAVLEDGE ♦ 



77 



Besides the fixed stars and their systems, straggling in 

 scattered groups on either side of the Milky Way or com- 

 posing its cloud-like arch, there are the vast masses of 

 glowing matter called, in contradistinction to the stellar 

 nebulte, which the telescope has resolved into stars, 

 gaseous nebulse. These are of regular and irregular 

 form — circular, elliptical, spiral, ftnd so forth ; they 

 are the raw stuff of which siius and systems are being 

 formed. These nebul» ; the fixed stars ; with whatever 

 appertains to them, and the vagrant bodies known as 

 comets, with their more or less associated meteor streams, 

 comprise the ponderable matter of the universe. The 

 sum-total of their radiant energy, save the small propor- 

 tion intercepted by one from the other, is ever in course 

 of transfer to the imponderable ethereal medium. 



The results of modern research into the structure of 

 the universe, in which inquiry Mr. Proctor has taken so 

 distinguished and important a part, and who therefore 

 speaks " as a man having authority and not as the 

 scribes," is thus summed uja by him in the article on 

 " Astronomy," contributed to the last edition of the 

 " Encyclopasdia Britannica" : — 



The sidereal system is altogether more complicated and more 

 varied in structure than has hitherto been supposed ; in>the same 

 region of the stellar depths co-exist stars of many orders of real 

 magnitude ; all the nebuhc, gaseous or stellar, planetary, ring- 

 formed, elliptical and spiral, exist within the limits of the sidereal 

 system ; and, lastly, the whole system is alire with movements, the 

 laws of which may cue day be recognised, though at present they 

 are too complex to be understood. 



THE SOLAR SYSTEM AXD ITS MEMBEES. 



The Sun is by no means the biggest of the stars, and, 

 as compared with them in brightness, he probably does 

 not exceed the third or fourth magnitude. But he has 

 the greatest interest and importance for u.s, seeing that 

 to him are due those manifold energies by which the 

 pirocesses of nature, both chemical and vital, are carried 

 on here and elsewhere. And, with the knowledge which 

 has been gained during late years concei'ning the same- 

 ness of the stuff of which nebula', stars, and planets are 

 spun, the nature and arrangement of the contents of our 

 solar system may enable us to make lawful analogies 

 concerning the contents of systems beyond it. The 

 Solar System comprises: 1, the Sun; 2, the Planets, 

 large, small, and minor; 3, Moons or Satellites; 4, 

 Comets, together with meteors or shooting-stars. 



The sun, whose volume exceeds several hundred times 

 all the other members of his system combined, is the 

 principal and indispensable source of ceaseless energy 

 radiant as light, heat, and chemical action, to them. 

 Of this energy the planets receive or intercept but the 

 2.30 millionth part, the earth receiving but the 2,170 

 millionth part, and even the larger proportion of this 

 energy is ultimately radiated by tliem into space. The 

 planets, one and all, revolve in nearly circular orbits, but 

 on rather differently inclined planes, round the sun, in 

 virtue of that energy of orbital motion with which each 

 was endowed at birth, and which counteracts the 

 opposing force of his gravitation, which would otherwise 

 pull them into him, absorbing them in his mass. Including 

 the swarm of minor planets or asteroids, of which new 

 ones are being frequently discovered, they are perhaps 

 to be numbered by thousands, and are of various sizes 

 and densities, and in different stages of progress and 

 decay. The evidence for the primitive gaseous state of 

 all bodies now possessing greater density w-ill be given 

 hereafter, but our system itself supplies illustration of 

 the passage of planets and satellites to an increasingly 

 solid form. Some, like our Earth and Mars, have cooled 



down sufficiently to be covered by a solid crust, and to be 

 fit abode for living creatures ; others, like Jupiter and 

 correspondingly huge bodies, are still in a more or less 

 heated and partly self-luminous condition. The smaller 

 bodies have long been cold and inert, like our airless, 

 barren moon. In her pale, reflected light and scarred sur- 

 face, illumined no longer by flame of central fires, we learn 

 that what she is, planets and the sun himself will one day 

 become. 



The moons revolve round their several planets under 

 similar restraint of force and freedom of energy as the 

 planets themselves. The gaseous masses composing 

 comets and meteor-streams travel in very eccentric orbits. 

 In fine, motion is everywhere, in ether, atom, mole- 

 cule, and mass ; the sun, like his fellow stars, has his 

 proper motion, carrying with him planets, satellites, and 

 whatever other bodies are within the curb of that force 

 of his gravitation which is itself obedient to the attrac- 

 tion of bodies perchance as much exceeding his own lu 

 power as he exceeds the mote dancing in his beams. 



THE EARTH. 



The mass of matter called the earth is of nearly 

 spherical shape, being slightly fiattened at the poles and 

 bulged towards the eqiiator. 



It consists of a core enclosed within, and connected 

 with, a cool, solid crust, three-fourths of which is covered 

 by a layer of water, and the whole surrounded by an 

 atmosphere. 



The entire mass, solid, liquid, and gaseous, spins on 

 its axis at the rate of about 1,000 miles every hour, and 

 speeds through space in its orbit round the sun at the 

 rate of 1,000 miles every minute. 



The atmosphere is composed, in the main, of the un- 

 combined elements oxygen and nitrogen ; the water is 

 chiefiy compounded of combined but mobile oxygen and 

 hydrogen. Of every hundred parts of the crust, ninety- 

 nine are made up of about sixteen out of the seventy 

 elementary substances, and of these sixteen the larger 

 number exist in small proportion. It is computed that 

 fully Que-half of the crust consists of oxygen which it has 

 taken into itself from the atmosphere, and that alreadv 

 one-third of the water of the ocean has been absorbed by 

 minerals. These are matters to be remembered when 

 dealing with the energies which have modified the 

 structure and composition of the framework of the earth. 

 The average density is about five times and a-half that 

 of a globe of the same size made of pure water, but the 

 large extent covered by the ocean in the southern hemi- 

 sphere, whither the tendency to collect was probably 

 manifest at the outset when the steamy vapours con- 

 densed ."tud filled the depressions in the crust, point to an 

 excess of solid matter in that direction. 



Wliat the inside of the earth is like no man can tell. 

 But it is probably solid throughout, and in a state rf 

 intense heat at no very great depth, as manifest in vol- 

 canic outbursts and allied phenomena. These show that 

 the earth has not yet lost the whole of the original store 

 of energy which it acquired during the aggregation of 

 the particles of which it is built up in their passage from 

 a diffused nebulous state to one of increasing densities 

 under the action of the force of gravitation. But the 

 escape of that energy through the crust to the ethereal 

 medium is unintermittent, and its final dissipation into 

 space is therefore only a question of time. 



The crust was probably never uniformly smooth, 

 because the contraction of the interior mass as it cooled 

 would bring about a state of tension causing shrinkage of 

 the surface. Hence would be the beginnings of those 



