Biot, Jean Baptiste (1774-1862), a French physicist, conducted research on magnetic fields and the effect of gas on light rays. A magnetic field is the influence that a magnet or an electric current creates in the region around itself. Biot also helped develop a measurement technique known as saccharimetry. That technique uses a form of light called polarized light to measure the concentration of sugar in a solution. Biot was also an expert on the application of physics to astronomy, and he studied the composition of meteorites.
Biot was born in Paris on April 21, 1774, and died there on Feb. 3, 1862. After military service as an artilleryman, he studied at the Ecole Polytechnique in Paris. He became a professor of mathematics at the University of Beauvais in 1797. In 1800, he became a professor of mathematical physics at the College de France. In 1808, Biot was appointed a senior member of the French Academy of Sciences.
In 1804, Biot accompanied the scientist Joseph Louis Gay-Lussac on a balloon ascent. The scientists discovered that there was no noticeable difference between Earth’s magnetic field at high altitudes and the field at sea level. They also analyzed the composition of the upper atmosphere during their ascent.
In 1806, Biot traveled to Spain with the French physicist Francois Arago to measure the length of one degree of longitude. This measurement led to the establishment of the length of the meter. In 1820, Biot and the French physicist Felix Savart discovered a fundamental law of electromagnetism. They found that the strength of a magnetic field created by an electric current passing through a wire is inversely proportional to the distance from the field to the wire. That is, the greater the distance, the weaker the field (see Electromagnet ). This relationship is known as the Biot-Savart law.
In Biot’s research on light, he measured the amounts by which different gases refract (bend) light rays passing through them. He also invented a form of polariscope, an instrument that can be used to examine substances in polarized light.
Polarized light can be thought of as consisting of light waves that vibrate in a particular way. Consider a beam of either polarized or nonpolarized light that consists of many individual waves. Each wave is made up of a vibrating electric field and a vibrating magnetic field. Each field vibrates in an imaginary plane. The two planes are perpendicular to each other, and both are perpendicular to the direction in which the wave is traveling. Now, consider only the planes in which the electric fields vibrate. If the beam is polarized, all those planes will be parallel to one another. But if the beam is nonpolarized, the planes will be offset from one another by many different angles.
Biot passed a beam of polarized light through a solution of sugar and observed the light with the polariscope. He noticed that the solution rotated the plane of vibration. He soon discovered that, the higher the concentration of sugar in the solution, the greater the angle between the “old” plane and the “new” plane. Thus, researchers could use the change in the angle of polarization as a measure of the strength of the solution.
