LITMIR.BIZ

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towards energy external to it; an attitude which results in its

       evasion of the retardative and dissipatory effects which prevail

       in lifeless dynamic systems of all kinds.

      _Other Minds than Ours_? attempts a solution of the vexed question

       of the origin of the Martian "canals." The essay is an abridgment

       of two popular lectures on the subject. I had previously written

       an account of my views which carried the enquiry as far as it was

       in

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      my power to go. This paper appeared in the "Transactions of the

       Royal Dublin Society, 1897." The theory put forward is a purely

       physical one, and, if justified, the view that intelligent beings

       exist in Mars derives no support from his visible surface

       features; but is, in fact, confronted with fresh difficulties.

      _Pleochroic Haloes_ is a popular exposition of an inconspicuous but

       very beautiful phenomenon of the rocks. Minute darkened spheres—a

       microscopic detail—appear everywhere in certain of the rock

       minerals. What are they? The discoveries of recent radioactive

       research—chiefly due to Rutherford—give the answer. The

       measurements applied to the little objects render the explanation

       beyond question. They turn out to be a quite extraordinary record

       of radioactive energy; a record accumulated since remote

       geological times, and assuring us, indirectly, of the stability

       of the chemical elements in general since the beginning of the

       world. This assurance is, without proof, often assumed in our

       views on the geological history of the Globe.

      Skating is a discourse, 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

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      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

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      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.

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      THE BIRTH-TIME OF THE WORLD [1]

       Table of Contents

      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

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