When at the request of your Committee I promised to read a paper before this Association, I asked our secretary how long he wished it to occupy. He said, “About half an hour, or a little more.” My first thought was, how am I to extend what I shall have to say over half an hour? But on beginning to put together my materials, I very soon found that the difficulty would be, not to fill half an hour, but to compress all, or anything like all, that there was to be said on the subject within that space of time. I shall, therefore, have to ask your indulgence for the necessarily incomplete, if not superficial, way in which I shall be obliged to treat my subject; to do it full justice would fill not a paper but a volume.