THE subject of the present Volume, although replete with interest, and of much practical importance, is one as to which we have no means of obtaining such complete and definite knowledge as to admit of it being presented in the shape of a systematic treatise. Some points may be considered as established with a sufficient degree of certainty; there are others as to which opinions may reasonably differ; while there is still a greater number as to which we must be content to acknowledge that, with our limited capacities, we have no means of forming an opinion at all.
The method of dialogue seems to be especially adapted for inquiries of this description; and it is hoped that this will be considered as a sufficient apology for the form in which the following observations are submitted to the public.