_It has been generally understood, that the author intended to have published this edition in octavo; but, the impropriety of adopting that mode must appear evident, for the very reason assigned by the author himself in the concluding part of his preface. If the plates are liable to sustain damage by folding them into a quarto, they would have been subjected to far greater injury by being doubled into an octavo size, besides, being extremely incommodious for reference. As the work now appears, the purchaser may either retain the plates in the separate volume, or, without much inconvenience, if properly guarded, have them bound with the letter press._ _It affords the editor a pleasing satisfaction to mention, that notwithstanding the additional heavy expense incurred in the article of paper, &c. yet, by somewhat enlarging the page, and other economical regulations in the mode of printing, this edition is offered to the public at a trifling advance on the original price, though the improvements now made occupy considerably more than one-hundred pages._ _Anxious, lest the reputation which the work has already acquired, should be diminished by any deficiency on his part, the editor has sedulously applied himself to render it extensively useful to the serious admirer of the wonders of the creation; whether he has succeeded, is now submitted to the decision of the intelligent part of the public. He shall only add, that conscious of the purity of his intentions, and convinced of the instability of all terrestrial attainments, he trusts that he is equally secured from the weakness of being elevated by success, or depressed by disappointment._ _Apothecaries Hall, London, Jan. 1, 1798._ CONTENTS. CHAP. I. A concise History of the Invention and Improvements which have been made upon the Instrument called a Microscope. p. 1. CHAP. II. Of Vision; of the optical Effects of Microscopes, and of the Manner of estimating their magnifying Powers. p. 26. CHAP. III. A Description of the most improved Microscopes, and the Method of using them. p. 64. CHAP. IV. General Instructions for using the Microscope, and preparing the Objects. p. 129. CHAP. V. The Importance of Natural History; of Insects in general, and of their constituent Parts. p. 167. CHAP. VI. A general View of the internal Parts of Insects, and more particularly of the Caterpillar of the Phalæna Cossus. A Description of sundry miscellaneous Objects. p. 334. CHAP. VII. The Natural History of the Hydra, or Fresh Water Polype. p. 357. CHAP. VIII. Of the Animalcula Infusoria. p. 415. CHAP. IX. On the Organization or Construction of Timber, as viewed by the Microscope. p. 574. CHAP. X. Of the Crystallization of Salts, as seen by the Microscope; together with a concise List of Objects. p. 600. CHAP. XI.