216 FKOM NEBULA TO NEBULA 



ranging from fractional ejections to profound disruption and 

 dispersion, according to the closeness of approach, the relative 

 masses of the bodies, and their internal state. The ejected parts 

 will pursue such courses as may be imposed on them by the new 

 forces of attraction brought into play by the changing relations 

 of the two bodies, both of which are necessarily in swift curving 

 motion, while one or both are losing mass by disruptive action. * * 



For an illustrative case, selected to suit our problem, let our 

 sun, in its ancestral state, be the body approached. For its 

 partner in action, let a more massive star be chosen and, for con- 

 venience, let it be so dense and inert that its response to the re- 

 action of the sun upon it may be neglected. In addition it will 

 be convenient to speak of the relative changes of position of the 

 two as if the whole motion were made by the passing star. * * * 



In selecting the closeness of approach, let us observe that 

 only 1/745 of the sun's substance was required to form our whole 

 planetary system. There are now known to be eight planets, 

 twenty-six satellites, and about eight hundred planetoids; prob- 

 ably the whole number of the latter may ultimately be found to 

 be a thousand or so. The average mass of these minor solar at- 

 tendants is thus only about 1/745,000 of the mass of the sun. 

 The average mass of the planets, neglecting the planetoids and 

 satellites, is about 1/6,000. Even the largest planetary mass is 

 less than a thousandth of the mass of the sun. It was not nec- 

 essary, therefore, that the sun should give forth even so much 

 as one-tenth of i per cent of its substance to form the largest 

 planet, assuming that the whole material for the planet was 

 ejected from the sun by a single impulse. The requirement for 

 the earth would be about one three-thousandth of i per cent of 

 the sun. It thus appears that the draft on the sun to supply the 

 substance of the planets was very small relatively. This suggests 

 that the passing star, if it had the mass we have chosen, must 

 surely have had such slight stimulating effect as the case re- 

 quired. We assume therefore only a quite distant approach. * * * 



Let it be assumed that the eruptivity of the sun was of the 

 same order then as now. At present, the sun is almost daily 

 shooting forth gas-bolts of vast dimensions and often at such 

 velocities that they rise many thousands of kilometers above its 

 glowing surface. Conservative computations assign these erup- 

 tive ejections velocities occasionally reaching one hundred or 

 two hundred kilometers per second, though the average speed is 

 less. Estimates by observers of high standing assign much 

 higher velocities in certain cases, some of these rising to several 

 hundred kilometers per second; indeed, velocities that surpass 

 the sun's power of control have been announced. * * * 



It is assumed that, at the time the nebula was formed, the 

 greater eruptions of the sun were concentrated, as now, in two 



