Page:Popular Science Monthly Volume 87.djvu/213

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THE

 

POPULAR SCIENCE

 

MONTHLY



SEPTEMBER, 1915



THE EVOLUTION OF THE STARS AND THE FORMATION OF THE EARTH[1]
By WILLIAM WALLACE CAMPBELL
DIRECTOR OF THE LICK OBSERVATORY, UNIVERSITY OF CALIFORNIA

Introduction

EVERY serious student of nature asks, sooner or later: What was the origin of the stars? What has been their history? And what does the future hold in store for them?

In harmony with our experience is the belief that all matter in the universe is endowed with the property of obeying certain fundamental laws, such as: every particle of matter attracts every other particle; a hotter body radiates its heat energy to a cooler body; gases expand indefinitely unless resisted by gravitation or other effective force. Again, everything in nature is growing older and changing in condition; slowly or rapidly, depending upon circumstances; the meteorological elements and gravitation are tearing down the high places of the Earth; the eroded materials are transported to the bottoms of valleys, lakes and seas; and these results beget further consequences. In general, the changes in small bodies proceed rapidly and in great bodies slowly.

Astronomers believe there has been an orderly development of the stars, in obedience to precisely the same simple laws that govern our every-day affairs. Starting with the materials as already existing, our problem is to trace in outline the probable course of the evolutionary processes which have given us the stellar universe.

The effort to find a solution brings us against two superlative difficulties:

First, save only the Earth and an occasional meteorite, all the bodies that concern us are at tremendous distances. We must study them at long range, through the reading and interpretation of the messages which their own rays of light and heat carry from them to us. We bring

  1. Second course of lectures on the William Ellery Hale Foundation, National Academy of Sciences, delivered at the meeting of the Academy in the University of Chicago, on December 7 and 8, 1914.