I quote in conclusion, Poincare’s final remarks: 

“The present state of the question is thus as follows:  the old theories, which hitherto seemed to account for all the known phenomena, have met with an unexpected obstacle.  Seemingly a modification becomes necessary.  A hypothesis has presented itself to M. Planck’s mind, but so strange a one that one is tempted to seek every means of escaping it; these means, however, have been sought vainly.  The new theory, however, raises a host of difficulties, many of which are real and not simply illusions due to the indolence of our minds, unwilling to change their modes of thought....

“Is discontinuity to reign through out the physical universe, and is its triumph definitive?  Or rather shall we find that it is but apparent and hides a series of continuous processes?...  To try to give an opinion just now on these questions would only be to waste ink.”

It only remains to call attention again to the fact that this conception of the discontinuity of energy, the acceptance of which Poincare says would be “the most profound revolution that natural philosophy has undergone since Newton” was suggested by the present writer fifteen years ago.  Its reception and serious consideration by one of the first mathematical physicists of the world seems a sufficient justification of its suggestion then as a legitimate scientific hypothesis.

THE ADVERTISEMENT OF IDEAS

Writing is a device for the storage of ideas—­the only device for this purpose prior to the invention of the phonograph, and not now likely to be generally superseded.  A book consists of stored ideas; sometimes it is like a box, from which the contents must be lifted slowly and with more or less toil; sometimes like a storage battery where one only has to make the right kind of contact to get a discharge.  At any rate, if we want people to use books or to use them more, or to use them better, or to use a different kind from that which they now use, we must lose sight for a moment of the material part of the book, which is only the box or the lead and acid of the storage battery, and fix our attention on the stored ideas, which are what everybody wants—­everybody, that is, except those who collect books as curiosities.  The subject of this lecture is thus only library advertising, about which we have heard a good deal of late, but we shall try to confine its applications to this inner or ideal substance which it is our special business as librarians to purvey.  And first, in considering the matter, it may be worth while to say a word about advertising in general.  Practically an advertisement is an announcement by somebody who has something to distribute.  Announcements of this kind may be classified, it seems to me, as economic, uneconomic and illegitimate.