THIS second series of lectures is meant to be the complement of the first, and indeed to be complement rather than sequel. True, I have made a few references to the first series in the present volume, and at the end of it I have said something about the mutual relations of the two series. Substantially, however, any reader of this book who had never heard of the first series would not be handicapped in any significant way. He might find the beginning of the second series indefensibly abrupt. That, I allow, would he due, in part at least, to the fact that there was a first series, which series, indeed, began in appropriately leisured fashion. But, in my judgement, awkward little things like that are incidental and not substantial. If I have failed in some such way, the cause is my own artlessness and is not interknit with my theme.