back This glossary contains descriptions of terms that have been used in the microscope section. Wherever possible, illustrations from early sources have been used to clarify the definition. Clicking on the small image will take you to a larger -- and often more complete -- illustration. Brass - An alloy of copper and zinc. Because of its vulnerability to tarnish it is usually coated with a clear lacquer finish on scientific instruments. Bull's eye condenser - A plano-convex lens of very short focus, it is used to focus light onto the subject being viewed. It can me used to cast a direct beam onto a specimen, or can be positioned to pass the light onto the mirror and then through the subject. To broaden a light source and smooth it out over a large area, such as the sub-stage microscope mirror, the plane side is kept toward the microscope. For throwing a pin point of light onto a specimen, the convex side is turned toward the subject and the plane side towards the light source. Used correctly, the bull's eye condenser can be a great asset in the control of lamp light or daylight. Camera Lucida - This attachment usually clips onto the eyepiece, and has a piece of neutral density glass that reflects part of the image to the eye, while, at the same time, reflecting the same image downward onto a piece of white paper. The viewer can then draw the image by tracing it. The oldest camera lucida for the microscope is Wollaston's. Coddington lens - A simple microscope lens invented circa 1829, and made of one piece of glass with two convex sides and a stop cut into the middle. German Silver - A brass type alloy with a silver color made up of copper, zinc, and nickel. It is more corrosion resistant that brass. The discovery of German silver dates to the early 19th
century and is attributed to the German chemist, E. A. Geitner.
Gillett's Illuminator or Condenser Stage forceps - The forceps attached to the stage or to the microscope. They had a tweezers on one end for holding a specimen for viewing under the lens. The other end was sometimes pointed for skewering a specimen. Lamps - Oil lamps were extensively used for lighting the microscopic subject, either directly or via the mirror. The light source is quite powerful, even when compared to modern electric lamps. Because the color temperature of lamp light is quite warm in color, a blue glass flue or filter was employed to shift the color toward daylight. Lieberkühn - A parabolic reflector that slips on over the lens so that a hole in the center of the reflector allows the lens to see the subject. Light that comes from below the slide is reflected back onto the specimen by the Lieberkühn reflector. Strictly speaking, the focus of each had to correspond the to a specific focal length of each lens. parabolic reflector The parabolic reflector is a sub-stage condenser that provides for dark field illumination. An adjustable center stop provides a dark field that is adaptable to various focal length. The parabolic lens passes the light around the field stop, and focuses it onto the slide. Side Reflector - The side reflector is a parabolic mirrored surface that reflects light onto the specimen. It attaches to the microscope and is positioned next to the lens in a way that allows it to focus the light onto the subject. Society of Arts Pattern - In1854 the London Society of Arts awarded a prize to G. Fields of Birmingham for an inexpensive microscope for medical students. The design requirements outlined a microscope that had two lenses, and could be disassembled and stored in a compact box. The instrument had to sell for a specified low price and the prize winner had to agree to keep the microscope always available for purchase. The popularity of the design was such that most manufacturers produced their own models with slight variations. Society thread - In1858 the Royal Microscopal Society standardized the thread size for screwing the objective into the microscope. The thread pitch is measured at 36 to an inch with a diameter of .8 inches. Modifications have been made to the standard over time, but it is essentially the same today as it was in 1858 so that lenses made from 1858 to the present day are interchangeable. Webster Condenser - A height adjustable achromatic condenser with a unique wheel of cut-out forms that allowed a wide variety of light controls. Turning the wheel would change the size of the diaphragm, give a wide variety of dark and light areas for oblique illumination, and also provided a dark field stop. This condenser was used primarily by Collins, and worked well with his binoculars. Wenham prism - This is the first successful and practical arrangement for binocular viewing in a microscope. It consists of a small prism, approximately 3/8" square, that fits into a drawer just above the nosepiece on the microscope lens barrel. The image then passes directly to the eye through the right eyepiece, and is bent by the prism so that the exact same image passes to the left eye. The image deflection was and angle of approximately 15 degrees. As a practical matter, this arrangement only worked well with low power lenses (1/2" or lower focal length). The prism slides out of the way by opening the prism drawer, which effectively converts the microscope into a conventional monocular. Zoophyte trough - Devised by Lister in 1834, the trough is made of two flat pieces of glass cemented narrowly apart. A third piece (not shown) is placed inside. The apparatus works like in miniature aquarium with spacer wedges that adjust the distance of the interior glass plate between the front and back. This action compresses the specimen for ease of focusing the microscope. back