72 



SCIENCE 



[N. S. Vol. LII. No. 1334 



a slow evaporation would eventually reduce a 

 star to an ordinary mass. The geologists give 

 the earth five hundred million years or more 

 in substantially its present condition so that 

 if it is slowly evaporating the time required 

 for it to completely disappear would be at least 

 of the order of magnitude which we have just 

 been discussing. Such evidence as we have, 

 however, indicates that the earth is growing 

 rather than diminishing. From the viewpoint 

 of our galaxy, a million billion (10^") years 

 would seem to be a reasonable unit of time. 



Once in a very long time a star through a 

 series of unfortunate encounters with other 

 stars will acquire so high a velocity that it 

 will escape from our galaxy altogether, and 

 like the lost Pleiad, wander hopelessly through 

 the ages in search of its sister stars ; but very 

 many of our astronomical time units will have 

 elapsed before this process could sensibly di- 

 minish the number of stars in the galaxy. 

 Whether or not the galaxy is already very old 

 as some of us thini, or whether it is relatively 

 young as is thought by others, it seems to be 

 fairly clear that in the course of time, at least, 

 it will be very old even as measured in our 

 very lengthy time units. As we muse upon 

 this certainty we wonder whether the light of 

 the stars will go out ; or will they continue to 

 shine in the remote ages to come. 



In the past a very great restraint has been 

 placed upon our vision by the gravitational 

 hypothesis as to the source of a star's energy. 

 According to this hypothesis the gravitational 

 potential energy of the star is converted into 

 the energy of heat and light and radiated 

 away. The entire life of our sun, at its pres- 

 ent rate of living, could not possibly exceed 

 fifty millions of years, and there is a similar 

 restriction upon all of the other stars. 

 Under no reasonable assumptions as to the 

 rate of expenditure could the period be ex- 

 tended to more than a few hundred millions 

 of years. At the expiration of this period the 

 star becomes a cold and solid body and remains 

 such until its very existence is snuffed .out in 

 some great catastrophe. It is much the same 

 as though a child were intellectually bright 

 for one, or two, or perhaps five minutes near 



the beginning of its life, and then all the rest 

 of its existence was spent in mental darkness ; 

 and this was true, not as an accident, but as a 

 regular thing. 



The discovery of the subatomic energies, as 

 manifested in the radioactive processes, some 

 twenty years ago has helped the situation 

 somewhat, lengthening the period of a star's 

 brilliancy two, three, five, perhaps ten times, 

 but that is all. The dismal picture remains, 

 notwithstanding the protests of the geologists 

 and the biologists, and the absolute failure of 

 the astronomers to find any evidences of these 

 cold and solid bodies and dead galaxies, which 

 should be vastly more numerous than the live 

 ones. But if the results are still unsatisfac- 

 tory the discovery and exploration of the sub- 

 atomic world has at least relieved us of a dog- 

 matism which could say, and once did say, 

 " You have so much time for your evolution, 

 and no more." It has opened our eyes to the 

 perception of new things, and awakened our 

 minds to new possibilities for which direct 

 physical evidence is still wanting. 



The doctrine of the conservation of energy 

 has been a well established doctrine among all 

 classes of scientists for seventy-five or eighty 

 years. Notwithstanding this, we have allowed 

 the greatest flow of energy with which we are 

 acquainted, the prodigious energy of the stars, 

 to escape into the blackness of space unnoticed 

 and forgotten, quite contrary to that some- 

 what more hazy doctrine which we call the 

 economy of nature. We simply did not 

 know what to do with it. Suddenly we dis- 

 cover that the atoms are wonderful organiza- 

 tions of energy. The vastness of their num- 

 bers, comparable only with the vastness of 

 astronomical space, suggests that their organi- 

 zation is an astronomical matter, for the as- 

 tronomers alone can furnish energy in suffi- 

 cient amount and equip a laboratory of 

 sufficient size. That the details of this equip- 

 ment are unknown need occasion no surprise, 

 but the products of this mighty laboratory 

 are visible upon the sky. Irregular nebulae 

 of gaseous materials occupying enormous vol- 

 imies of space are found in abundance there, 

 and much evidence of dark nebulosity against 



