The Birth-Time of the World | Page 3

with a recent addition supporting the original thesis. It is an illustration of a common experience--the explanation of an unimportant action involving principles the most influential considered as a part of Nature's resources.
The address on The Latent Image deals with a subject which had been approached by various writers before the time of my essay; but, so far as I know, an explanation
xiv
based on the facts of photo-electricity had not been attempted. Students of this subject will notice that the views expressed are similar to those subsequently put forward by Lenard and Saeland in explanation of phosphorescence. The whole matter is of more practical importance than appears at first sight, for the photoelectric nature of the effects involved in the radiative treatment of many cruel diseases seems to be beyond doubt.
It was in connection with photo-electric science that I was led to take an interest in the application of radioactivity in medicine. The lecture on The Use of Radium in Medicine deals with this subject. Towards the conclusion of this essay reference will be found to a practical outcome of such studies which, by improving on the methods, and facilitating the application, of radioactive treatment, has, in the hands of skilled medical men, already resulted in the alleviation of suffering.
Leaving out much which might well appear in a prefatory notice, a word should yet be added respecting the illustrations of scenery. They are a small selection from a considerable number of photographs taken during my summer wanderings in the Alps in company with Henry H. Dixon. An exception is Plate X, which is by the late Dr. Edward Stapleton. From what has been said above, it will be gathered that these illustrations are fitly included among pages which owe so much to Alpine inspiration. They illustrate the
xv
subjects dealt with, and, it is to be hoped, they will in some cases recall to the reader scenes which have in past times influenced his thoughts in the same manner; scenes which in their endless perspective seem to reduce to their proper insignificance the lesser things of life.
My thanks are due to Mr. John Murray for kindly consenting to the reissue of the essay on _The Birth-time of the World_ from the pages of _Science Progress_; to Messrs. Constable & Co. for leave to reprint Pleochroic Haloes from Bedrock, and also to make some extracts from _Radioactivity and Geology_; and to the Council of the Royal Dublin Society for permission to republish certain papers from the Proceedings of the Society.
_Iveagh Geological Laboratory, Trinity College, Dublin._
July, 1915.
xvi
THE BIRTH-TIME OF THE WORLD [1]
LONG ago Lucretius wrote: "For lack of power to solve the question troubles the mind with doubts, whether there was ever a birth-time of the world and whether likewise there is to be any end." "And if" (he says in answer) "there was no birth-time of earth and heaven and they have been from everlasting, why before the Theban war and the destruction of Troy have not other poets as well sung other themes? Whither have so many deeds of men so often passed away, why live they nowhere embodied in lasting records of fame? The truth methinks is that the sum has but a recent date, and the nature of the world is new and has but lately had its commencement."[2]
Thus spake Lucretius nearly 2,000 years ago. Since then we have attained another standpoint and found very different limitations. To Lucretius the world commenced with man, and the answer he would give to his questions was in accord with his philosophy: he would date the birth-time of the world from the time when
[1] A lecture delivered before the Royal Dublin Society, February 6th, 1914. Science Progress, vol. ix., p. 37
[2] De Rerum Natura, translated by H. A. J. Munro (Cambridge, 1886).
1
poets first sang upon the earth. Modern Science has along with the theory that the Earth dated its beginning with the advent of man, swept utterly away this beautiful imagining. We can, indeed, find no beginning of the world. We trace back events and come to barriers which close our vista--barriers which, for all we know, may for ever close it. They stand like the gates of ivory and of horn; portals from which only dreams proceed; and Science cannot as yet say of this or that dream if it proceeds from the gate of horn or from that of ivory.
In short, of the Earth's origin we have no certain knowledge; nor can we assign any date to it. Possibly its formation was an event so gradual that the beginning was spread over immense periods. We can only trace the history back to certain events which may with considerable certainty be regarded as ushering in our geological era.
Notwithstanding our limitations, the date of the birth-time of our geological era is the most