Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. When through a long period of time one has been a constant student of some particular subject, it becomes extremely dificult to attribute to their right sources all the ideas concerning it in possession of which one happens to find oneself, - and quite out of the ques tion if the possible sources are numerous. Besides, in common politeness to oneself one must consider some of the ideas home-grown, even though they resemble ideas to be found elsewhere. I have, however, done my best to acknowledge all conscious borrowings; and if it is to be my unhappy fate to have others brought to my consciousness later on, I apologize beforehand, and will make due reparation in other editions.