66 ILLINOIS STATE ACADEMY OP SCIENCE 



with wliicli the electrons are known to move suggests 

 that at the instant of collision the electron would be mov- 

 ing with the speed of light, and under this assumption 

 the kinetic energy at the instant of collision can be com- 

 puted. It is found that if a gram of matter should lose 

 the property of mass in this manner the energy liberated 

 would be equivalent to five billion calories of heat, and 

 the present mass of the sun would contain sufficient 

 energy to last at its present rate of radiation five billions 

 of years. 



According to the present hypothesis, therefore, the 

 energies of the stars are obtained at the expense of their 

 masses, and if the masses were not somehow renewed 

 the life, by which we mean the period of its luminescence, 

 of a star would be limited just as certainly as it is lim- 

 ited under the contraction hypothesis. It is known, how- 

 ever, that vast regions of space are nebulous and it 

 seems quite probable that all space is more or less 

 nebulous. We have only to suppose then that the amount 

 of matter gathered in by a star in its journey through 

 space is equal on the average to the amount that it loses 

 through the process of radiation in order to account for 

 an indefinite duration of luminescence. It is not neces- 

 sary to suppose that the mass of a star is constant. If 

 it plunges through a richly nebulous region its mass will 

 grow with relative rapidity and its rate of radiation will 

 increase, but if it should wander for several billions of 

 years in a region Avhich was virtually empty it would de- 

 cline in radiation and ultimately reach the point when its 

 lijjht was extinguished. But it would brighten up again 

 when the conditions were again favorable and its life 

 would be renewed. Periods of darkness and periods of 

 luminescence might succeed one another indefinitely. 



The ultimate source of the stellar energies is to be 

 found, therefore, in the energies of the organization of 

 the atoms of the nebulae, and not in their gravitational 

 potential energies. Space would eventually be swept clean 

 of its nebulosity by the stars if its renewal were not 

 provided for in some manner. Indeed, it is evident that 

 the origin of nebulosity is as vital a problem in cos- 



