This book is one of those which, if it lives for a number of decades, and if it requires any Preface at all, wants a new one every ten years.

The first Preface to a book is apt to be explanatory, perhaps apologetic, in the expectation of attacks from various quarters.

If the book is in some points in advance of public opinion, it is natural that the writer should try to smooth the way to the reception of his more or less aggressive ideas.

He wishes to convince, not to offend,--to obtain a hearing for his thought, not to stir up angry opposition in those who do not accept it.

There is commonly an anxious look about a first Preface.