In a presidential address delivered before this Society not long ago, the former speaker divided such addresses into two groups. To the one belonged those in which the retiring president sought to develop some favorite theory of his own; to the other those which in general treated of the progress of some particular science or branch thereof.
The address which I have to present this evening belongs, I believe, to the second group, although I may trespass slightly on the field of the first by suggesting a few ideas for your consideration. If they arouse discussion, so much the better, as it may lead more rapidly to a true solution of some of the problems referred to.
I make no apologies for the selection of my topic, because it represents a field in which my interests lie, but it is unfortunately one in which, as a whole, few specialists . . .