126 SCIENCE AND IMMORTALITY 



and elongated by the larger, but strained to such 

 an extent that it bursts into fragments. The 

 fragments of the elongated rotating mass will 

 necessarily take on a whirling or spiral motion, and 

 " when the explosive eruption occurs the two pro- 

 tuberances or elongations of the body will fly 

 apart, and having also a rapid rotatory movement, 

 the resulting spiral will necessarily be a double 

 one." 



The mere formation of a spiral is easy to account 

 for. Almost any collision, says A. R. Wallace, 

 between unequal masses of diffused matter would, 

 in the absence of any massive central body round 

 which they would be forced to revolve, lead to 

 spiral motions. 



Sir Robert Ball explains the spiral thus. On 

 ordinary mechanic principles, any globular collec- 

 tion of promiscuously revolving particles will tend 

 to flatten down into a disc, with particles all re- 

 volving in one direction ; and since the central 

 mass would revolve more rapidly, the general 

 circulation of the particles would come to have a 

 spiral direction. 



But it is not sufficient to account for the spiral, 

 we must also account for its two-armed structure, 

 and these can only be " the outcome of long- 

 continued, oppositely-directed eruptions." 



The manner in which the nebulae are converted 



