To every beginner I would have it pointed out that the principles which are set forth in Part I. constitute absolutely the alphabet of microscopy. I would have such beginner appreciate that the magnified image which is formed upon the retina of the observer is rightly considered the joint creation of the optician and the microscopist. I would have him learn that it is for the microscopist to develop upon the stage of the microscope the pattern of radiant points (spoken of above as the stage-picture) ; and for the optician to take in charge the beams which proceed from that stage-picture, and to form out of these the magnified "microscopic image" I would further have it brought home to every beginner that if he fails to develop upon the stage of the microscope a stage-picture, no effort on the part of the optician will conjure up an image; while given a satisfactory stage-picture, even the poorest of microscopes will furnish something to the eye.
Upon the more advanced microscopic worker I would have it impressed that, while it holds true generally that the stage-picture is the concern of the microscopist and the microscopic image the concern of the optician, this statement does not embrace the whole truth. The microscopist has also a responsibility in connexion with the development of the microscopic image, in particular in the case where the high powers of the microscope are employed. Here the optician must perforce count upon the intelligent co-operation of the microscopist.
The general subject matter of my work enunciated, I would desire to explain also certain features in connexion with its exposition.
If the reader demurs to being called upon to begin both in Part I. and Part II. with subject matters which are not directly relevant to the microscope, I would explain that this is done with a view to avoiding the treatment of these questions in a parenthetical manner. The reader will appreciate that the art of exposition is the art of avoiding parentheses.
If, again, the reader sees ground of complaint in the fact that he is required at every moment to put down the book and undertake an experiment, I would submit that no proposition is adequately
