Optical instruments

   Optical instruments are devices in which light is passed through lenses or prisms. Among the common optical instruments are the microscope, binoculars, camera, spectroscope, periscope, and telescope.

   In the 1500's and 1600's, the first optical instruments were developed, following the discovery of the glass lens. The earliest telescopes and microscopes evolved because of the lens.
   One of the original optical instruments to undergo numerous improvements was the spectroscope. In 1666 Isaac Newton sent a beam of light through a prism. The beam broke into a band of colored light, similar to a rainbow.

   One kind of SPECTROSCOPE is basically a glass PRISM. All materials, when heated hot enough, radiate light. When this light from a particular substance is beamed through a prism, it divides into colored areas that are distinct for the elements in that substance. A trained spectroscopist can use this instrument to determine the chemical composition of laboratory "unknowns" and the elements in the stars and the sun.

   Intensity of light is measured by one or another type of light meter. Photoelectric-cell meters convert light to electricity, and then the light strength is read on a dial. A laboratory PHOTOMETER compares a standard light source at a given distance with an unknown light at a measured distance; then by use of the inverse square law, the strength of the unknown light can be figured. Measurement units of intensity for light instruments are either in FOOT CANDLES or in the new units, candelas.

The speed of light can be measured by an optical instrument developed by Albert A. Michelson of the University of Chicago. He determined that light in a vacuum travels at the speed of 186,284 miles per second.

   Some instruments use polarized light. This is ordinary light that has been passed through a device that makes all its waves vibrate in one direction only instead of moving in several planes. This is done by directing the light either through crystals having a slit-like molecular arrangement, or else through plastic sheets coated with certain chemicals. Polarized light devices include camera filters, glare-reducing sunglasses, and car headlights. Biochemists use it in an instrument that measures strength of sugar solutions. Engineers who work with construction and manufacturing materials use polarized beams to reveal strains in glass and plastics.

   From the time of Columbus to the present, optical instruments have become increasingly important to the scientist. He relies upon the microscope to see the micro, or small world, and upon the telescope to see the universe. Many discoveries in atomic physics, and in chemistry are due to the spectroscope. An even smaller world is now visible with the electron microscope.

   Eye glasses, cameras, and binoculars are examples of the modern uses and improvements in optical instruments.