Spectroscope c. 1885 John Browning, London Brass, glass prisms Used to separate and observe the visible colored spectrum of light beams. The prism assembly is 10” in diameter, the instrument is 14” high, the collimator and telescope are 12” long and 1” in diameter. The prisms are 3” high x 1” per side. Spectroscopes are used to study the wavelengths of light beams. To do this they incorporate a dispersion prism or multiple dispersion prisms in the light beam's path. The prism splits the light into it's fundamental wavelengths when it is at the correct angle to the beam. Each wavelength appears as a different colored stripe or band in the telescope eyepiece. Since each element has a unique wavelength, spectroscopes were used to study the purity and chemical makeup of many elemental materials. In many instances, the material to be studied was solid matter. In order to process it for analysis by the spectrometer, the studied materials were ground to a very fine powder that was then ignited. The light beam from the flame was then analyzed by the spectroscope. Spectroscopes are also one of the most important contributors to the field of astronomy. Spectroscopy, the use of light from a distant object to understand what the mineral content is, could be the single most powerful tool astronomers have used. Without spectroscopes, we would know very little about the makeup of the stars. The spectroscope shown here is a spectacular and rarely seen, six-dispersion prism instrument by a most important maker. It is a striking combination of golden lacquered brass, gray tinted brass and six, precision glass prisms. The instrument is in excellent original condition. Engraved in the brass center piece is the maker's signature, 'John Browning London'. The six dispersing prisms are held within a brass circular, double frame. The prisms are mounted on brass fixtures that sit on an opaque, circular 1/4” thick glass plate. The prisms sit on linkage adjustable mounts and are moved by an interesting mechanism that controls every prism simultaneously. The mechanism compensates for the location of each prism so that each prism's light path remains constant as the spectrum is adjusted. This requires a complex linkage as each prism is moved a different distance and angle relative to the other prisms (see linkage photo). The linkage system is adjusted by a 5-1/2” long, fine thread screw which is turned by a thumb nut. The linkage system is attached to the screw by a clamp that can release or clamp the screw. In addition to the six dispersion prisms there are three Porro prisms. One is a single Porro prism and the other is a double, with one prism mounted on top of the other. The spectroscope is designed so that the double Porro prism slides into dovetail joints behind each dispersing prism causing it to interact with any of the six prisms. If it is installed behind the sixth dispersal prism, there are twelve passes of the light beam through the lower portion of the dispersal prisms before the spectrum is read by the telescope. The single Porro prism can be added to a special dovetail joint in front of the first dispersal prism. It reverses the beam after the twelve passes, causing the light to be again passed through the top half of the dispersal prisms for up to twenty-four passes. This ability to move the Porro prisms around the instrument allows the user to pass the light beam through any combination of one dispersal prism, (two passes) up to six dispersal prisms and twenty four light beam passes. The theory behind this design is that the more passes the light makes through the prisms the better the spectrum resolution. The telescope consists of an eyepiece and an objective lens. There are fine cross hairs in the telescope. The eyepiece is adjusted by a thumb screw rack and pinion motion. The telescope can be mounted in two positions (upper and lower) on the instrument. The lower position observes the lower portion of the prisms and can view up to twelve light passes (six prisms). The upper location reads the upper part of the prisms where the light path has been doubled for up to twenty four passes. The collimator has a removable shroud at the incoming light beam end. The slit opening is controlled by a small thumb screw dial indicator. Maximum slit width is well under 1/64th of an inch. There is a swing-away miniature prism that can be moved in front of the slit covering about 1/3rd of the length. We assume that this is a reference prism used to check the relationship between the collimator and the telescope. There is a lens at the exit end of the collimator. A regular right-angle prism deflects the light beam from the collimator to the lower half of the first dispersing prism. There is an accessory that is a reference prism. It is used to project a calibration spectrum to the telescope so that the spectrum from the collimator and the reference prism can be viewed simultaneously. It is 4-1/2” long and 5/8” in diameter. At one end is a complex slit assembly that is adjusted with a recording dial indicator. At the other end is the small reference prism. It is designed to be easily removable from the instrument using a thumb screw clamp and slide joint arrangement. John Browning stated in his catalog that this multi-prism instrument has the advantage of doing every class of spectrum work in the laboratory and observatory and at a higher resolution. When experimenting with the instrument I was able to resolve a bright spectrum with up to twelve light beam passes. It would take an experienced user to focus the light beam through the full twenty four passes and into the reading telescope. The instrument includes the original dove-tailed wooden box that is 14” x 15” x 16” high. There are two large brass handles on the sides. The spectroscope sits on a circular wooden base that slides in and out of the box. There are slots and brackets that hold the telescope, collimator, reference prism and the various lenses. Per Wikipedia; John Browning 1831-1925, born in England. Son of an important nautical instrument maker. Graduated from the Royal College of Chemistry. Apprenticed with and eventually joined his father William Spencer Browning in the family business. In 1856, John became the sole owner of the business which was located in London. He designed and manufactured telescopes, microscopes, barometers, photometers, cameras, ophthalmoscopes, and electric lamps. He was perhaps best known as the highest quality manufacturer of spectroscopes in England. He also published books, training manuals and catalogs about the use of spectroscopes which were widely used by spectroscopists. Later on, he became an important maker of ophthalmic instruments, including spectacles. He was a member of the Royal Astronomical Society and several other scientific related organizations. He was the Optical and Physical Instrument Maker to Her Majesty’s Government. He sold his company around 1900 to W. Watson & Son.