The nineteenth century witnessed vast improvements in microscope design and function. Objectives and condensers were being built with multiple lenses that had increasing degrees of optical correction. Photomicrography made its debut in mid-century and by the end of the nineteenth century, high-end microscopes performed better than many student models produced today. The first part of the nineteenth century witnessed dramatic improvements in optics with the introduction of achromatic objectives by van Deijl, Amici, and Lister that also raised numerical apertures to around 0.65 for dry objectives and up to 1.25 for homogeneous immersion objectives. Innovations in machine tooling led to greatly improved design and construction of the microscope’s mechanical elements and many well-crafted instruments appeared by designers such as Beck, Chevalier, Nachet, Leitz, Powell & Lealand, Ross, and Zeiss. In 1886, Ernst Abbe’s work with Carl Zeiss led to the production of apochromatic objectives based, for the first time, on sound optical principles and lens design. These advanced objectives provided images with reduced spherical aberration and free of color distortions (chromatic aberration) at high numerical apertures. At the end of the century, in 1893, Professor August Köhler reported a method of illumination, which he developed to optimize photomicrography, allowing microscopists to take full advantage of the resolving power of Abbe’s objectives. The last decade of the nineteenth century saw innovations in optical microscopy, including metallographic microscopes, anastigmatic photolenses, binocular microscopes with image-erecting prisms, and the first stereomicroscope.

DELLEBARRE MONOCULAR BRASS COMPOUND MICROSCOPE The elegantly crafted monocular brass compound microscope was manufactured by Louis F. Dellebarre sometime around 1777. The model featured was redrawn from photographs of the original microscope, which is part of the Billings microscope collection at Walter Reed Army Hospital in Washington DC. The microscope is similar in design and execution to Dellebarre’s Dutch Microscope made in 1795 and described elsewhere in the museum. A three-leg brass tripod base, attached to the bottom of the square pillar, supports the microscope. Positioned at the lowest portion of the pillar is a substage double mirror, which swings on a gimbal and is attached by a double compass joint. A double convex lens above the mirror serves as a condenser to focus light on a specimen positioned on the circular stage. The stage is hinged to fold upward and is supported on a box slide that is translated with a rack mechanism. A sliding arm holds the body tube using a leather-lined split ring with a spring catch and screw clamp. The body tube is composed of three sections: a nosepiece for the Lieberkühn reflector and objective, a central support tube, and the eyepiece tube. These sections may be separated to increase the tube length of the microscope. The eye lens is bi-convex and is mounted in a bezeled cell and covered with a screw cap and sliding dust cap. Although not achromatic, the microscope was termed the Universal model. JOHN DOLLOND MONOCULAR COMPOUND MICROSCOPE This early nineteenth century Dollond microscope was considered to be among the finest optical instruments developed prior to the introduction of achromatic microscope objectives. The featured model was redrawn from photographs of the original microscope, which is part of the Billings microscope collection at Walter Reed Army Hospital in Washington DC. Exhibiting excellent workmanship, the monocular compound microscope is similar in design and execution to the “Jones Most Improved” instrument series and is signed on the base, “Dollond, London“. A folding tripod base anchors the circular pillar that is surmounted by a compass joint. Affixed to the joint is a short arm that suspends a limb measuring 10-1/2-inches in length. A double mirror about 2-inches in diameter is clamped onto a sleeve positioned at the lower end of the limb.Illumination is concentrated by a 1-1/2-inch diameter condenser secured on an adjustable angled limb located above the mirror. The body tube affixes at the nose to the upper portion of the limb and remains stationary. There is no drawtube and focus is accomplished by adjusting the stage position in relation to that of the objective by turning a pinion located on the stage sleeve. Additional optical features include an eyepiece that is comprised of three lenses and a field lens. S. J. RIENKS MONOCULAR COMPOUND MICROSCOPE This brass microscope was made in Holland and is signed “S. J. Rienks, Friesland, 1825″. The model featured below was redrawn from photographs of the original microscope, which is part of the Billings microscope collection at Walter Reed Army Hospital in Washington DC. This unusual microscope is constructed according to the design of the Dr. Robert Smith reflecting microscope with a folding telescopic tripod base. Dr. Smith was an English instrument maker and author of System of Optics, published in London in 1738. The upper end of the body tube holds a large concave mirror, and the lower end a small convex mirror. The underside of the smaller mirror is ground to form a concave mirror to act as a Liberkühn reflector. A central stop (supported by a wire) blocks direct light from passing to the eyepiece. A short tube carries the spring-loaded stage, and the microscope is focused by a rack and pinion gearset. The double mirror, constructed of speculum metal, is attached to one of the legs by means of a thumbscrew.