text:  If an author has many different and opposite subjects of interest in his head which is not unfrequently the case with persons of the higher order of intellect and he can discant on all with equal facility or investigate all with equal eagerness he will do well to recollect that the minds of his readers are not likely to be equally discursive and that he is apt to destroy the influence or mar the effect of each if he blends them together; separation of works is the one thing needful there