Illustrated Scientific and Descriptive Catalogue of Achromatic Microscopes manufactured by J. W. Grunow & Co., New Haven, Conn., 8vo, pp. 104.—This work deserves honorable mention as a treatise of no small merit upon the general principles of optics involved in the Construction of the microscope. This subject is considered under the following heads. Chapter I. Theory of the Microscope. Chapter II Mechanical structure of the Microscope. Chapter III. Accessory apparatus. Chapter IV. Polarized light and its application to the Microscope. Chapter V. Practical directions. Eight distinct forms of the microscope, all original with these artists, are described and figured with their accessory apparatus. These are, No. 1, Educational microscope. No. 2, Students microscope. No. 3, Student's microscope. No. 4, Student's larger microscope. No. 5, Another form of student's microscope. No. 6, Portable microscope. No. 7, Large microscope. No. 8, Simple form of inverted microscope; to which may be added the more complete inverted microscope. The figures in this treatise are all original drawings by Sanford from the Instruments, and are remarkably good examples of the xylographic art. These artists have attained a most enviable perfection in all the nicer details of construction in the mechanical portion of the instrument, while in the optical department they have also obtained the most satisfactory results. There are points of great interest to the microscopist discussed in their Catalogue which we may hereafter transfer to our pages. Such is § 124, on the " Qualities of Object-glasses." Several novelties of construction are also for the first time here described and figured. The book is beautifully printed, and will be sent by post to any address upon the transmission of thirty cents in stamps to the artists.