HA RD WICKE ' S S CIENCE- G O SSI P. 



planetary system is constantly radiating heat into' 

 surrounding space. It is not necessary to more than 

 mention the well-established fact that both the 

 earth and moon were formerly incandescent. The 

 flattening of the poles absolutely demand at least a 

 fluid body for their formation, and the observed 

 facts of geology uniformly corroborate the former 

 incandescent state of the earth. The sun is pouring 

 away heat at such a rate that, according to Sir John 

 Herschel, if a cylinder of ice 184,000 miles in length 

 and 45 miles in diameter were darted into it every 

 second, the ice would be melted as fast as it came ; 

 and although this enormous loss is partly compensated 

 by heat due to the arrested motion of meteors falling 

 upon the sun's surface, it is by no means probable 

 that the sun is in this way compensated to any note- 

 worthy extent. The dissipation of motion in the 

 form of heat is always and necessarily accompanied 

 by the concentration of matter. All cooling bodies 

 diminish in size and increase in density. All 

 contracting bodies generate heat by the friction of 

 their particles upon each other. The loss of this 

 heat by radiation allows the process of contraction 

 to continue ; so that the further back we go, the 

 larger and less solid must have been the sun and the 

 planets, until, if in a state of diffused vaporous matter, 

 we may well understand that the present solar system 

 might have once been a nebular mass extending far 

 beyond the orbit of the outermost planet. So that, 

 observing what is now going on, shows clearly that 

 the solar system might formerly have consisted of a 

 nebulous mass. 



It is established that there are hovering cloud-like 

 in space vast masses of self-luminous vapour or 

 nebulae ; and not only nebulae, but nebula? in all states 

 of development. The spectroscope has established 

 the fact that certain nebulae are gaseous. In 1S64 

 Mr. Huggins found that the nebula in Draco gave a 

 spectrum of bright lines, due to nitrogen, hydrogen, 

 and one other unknown element, which proved the 

 caseous or irresolvable condition of the nebula. The 

 spectrum of other nebulae show, beneath the bright 

 line spectrum of a gaseous nebula, a faint continuous 

 spectrum, proving a more condensed state, and so on, 

 gradually approaching the condition of our sun. 

 Lieutenant Herschel observed in the southern Heavens 

 a clustering nebula with a continuous spectrum, 

 showing the presence of various metals, on which he 

 could just detect the three bright lines seen in the 

 spectra of the gaseous nebulae. Cooler suns show that 

 free hydrogen is missing ; and, in short, there are 

 exhibited various stages of condensation from the 

 gaseous nebulae to suns such as our own showing that 

 the various orders of nebulae are orders of but a single 

 family, and that there is one and only one order of 

 matter throughout the universe, though in various 

 stages of development. Further, Le Sueur of 

 Melbourne proved before 1870 that the irregular 

 nebulae are variable ; and finally, in the magnificent 



photograph obtained by Mr. Roberts of the nebula 

 in Andromeda, we have actually seen a nebula broken 

 up into rings, with one ring partly condensed into a 

 planet, and with other planets formed outside, where 

 the rings have entirely disappeared. It may now be 

 fairly stated that the series from nebulae to planets is 

 fully established. Sir William Herschel was struck by 

 the circumstance that, after sweeping over a part of 

 the heavens which was unusually barren of stars, he 

 commonly met with nebulae, insomuch that it was his 

 practice at such times to call to his assistant (his sister, 

 Miss Caroline Herschel) " to prepare for nebulae." Mr. 

 Proctor adds that, " in fact, the nebulae, in a sense, 

 represent the missing stars, and that the region where 

 those nebulae appear has been drained of star- 

 material, so to speak, in order to form them." 



We have established, then, the existence of irregular 

 nebulae which are variable — that is, the various parts of 

 which are in motion. To proceed a step further, we 

 know that the solar system has been pouring out heat 

 at such an enormous rate that in the past it must have 

 been so much hotter than at present that we may 

 fairly assume its prior condition as a gaseous or 

 nebulous mass. The heat must have been too great 

 to allow of it being a solid cr even a liquid body. 

 Now, with the parts of the nebula in motion, whether 

 the motion is in the form of currents determined 

 hither and thither according to local circumstances, 

 or in any other conceivable way, such motions bearing 

 some reference to a common centre of gravity, unless 

 the currents exactly balanced each other — a supposition 

 against which the chances are as infinity to one — one 

 set must eventually prevail over the other, and the 

 mass must at last inevitably assume the form peculiar 

 to rotating bodies, in which the particles move freely 

 upon each other. It must become an oblate spheroid 

 flattered at the poles and bulging at the equator, 

 rotating faster and faster as it contracted. In some 

 such manner as this our solar system acquired its 

 definite rotation from west to east. A very curious 

 physical experiment devised by M. Plateau strikingly 

 illustrates the growth of our planetary system from 

 the solar nebula. M. Plateau's experiment consists 

 in freeing a fluid mass from the action of terrestrial 

 gravity, so that its various parts may be subject only 

 to their own mutual attractions, and then in imparting 

 to this mass an increasingly rapid movement of 

 rotation, A quantity of oil is poured into a glass 

 vessel containing a mixture of water and alcohol, of 

 which the lower strata are heavier than the oil, while 

 the upper strata are lighter. The oil when poured in 

 descends until it reaches the stratum of the same 

 density with itself, when, being freed from the action 

 of terrestrial gravity and subjected only to the mutual 

 attraction of its own molecules, it assumes a spherical 

 form. By an ingenious mechanical contrivance, M. 

 Plateau causes the sphere of oil to rotate about its 

 own centre of gravity. While the movement is slow, 

 the excess of centrifugal force at the equator of the 



