160 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
the arrangement of the solar system in a very gratifying way. It 
was, however, until quite recently, open to one very serious objection. 
The distances of the stars from one another are enormously great in 
comparison with their dimensions. If we take six cricket balls and 
place one each in Europe, Asia, Africa, Australia, North America, 
and South America, we have a model showing the arrangement of 
the six stars nearest to our sun and their distances apart relative to 
their dimensions. Since the stars are generally very many of their 
diameters apart, it must be a very rare event for their tracks to come 
to within a few diameters of one another, and yet the tidal theory 
requires an approach to within less than two diameters before planets 
can be born. Under the old views as to the ages of the stars it was 
exceedingly unlikely that a specified star such as our sun should have 
experienced so close an approach throughout the whole of his life, 
and this constituted a serious objection to the tidal theory. But the 
recent extension of the ages of the stars has removed this reproach; 
stars which have wandered about amongst other stars for millions 
of millions of years must be expected to have had several fairly close 
approaches to their neighbors. Jiven now, however, approaches of 
the extreme closeness necessary to give birth to planets must be 
counted as somewhat rare; a small proportion only of the stars in 
the sky are likely to be surrounded by families of planets and so to 
form possible abodes of life. 
At one time it seemed possible that cosmognony might come down 
from her lofty pedestal and make good for her former deficiency in 
the matter of utilitarian gifts by bringing the most utilitarian gift of 
all—the secret of obtaining free energy. Jor if the stars are inces- 
santly turning matter into energy, there would seem to be no reason 
why mankind should not learn their secret, and obtain mechanical 
power by annihilating small quantities of matter instead of labori- 
ously winning, transporting, and burning millions of tons of coal; 
the total consumption of coal in the British Isles produces less heat, 
light, and energy than could be obtained by the annihilation of an 
ounce of matter per day. But, so far as can at present be seen, this 
dream is not destined to be fulfilled. An analysis of the facts of 
astronomy suggests that there must be all sorts and types of matter 
mixed together in the stars; some only, not all, of these types are 
changing into energy at an appreciable rate, and these particular 
types, for good or for bad, are absent from our earth. They prob- 
ably consist of elements heavier than uranium, the heaviest element 
known on earth; it is even possible that the capacity for spontaneous 
disintegration shown by the atoms of uranium and the other radio- 
active elements, the heaviest of terrestrial substances, may represent 
the surviving vestiges of an earlier power of these same atoms to 
lessen their mass by throwing off radiation. 
