A didactic purpose and a literary one, do not always run readily side by side. A teacher who desires to inculcate certain principles or ideas, is ever on the look out for illustrations and recurs to his topic again and again. So, having, as I thought, certain topics to teach, I have brought them back into view more often than I should have done if I had written solely with a literary view. I have not commonly given accounts of what has been said by others on the points of which I treat, or criticised conclusions different from mine, for I know that this manner of treatment is not in favour with the present generation. I recollect the reason of an undergraduate, in my early days, for preferring the instruction of his private tutor to that officially provided The Lecturer tells you that Hermann says it is this, and Wunder says it is that, but Blank (the private tutor) tells you what it is.