March 5 is Jacques Babinet’s birthday. Babinet was a French physicist who is best known for his study of optics. Among his contributions was the proposal to adopt the wavelength of light as the basis for a standard of measurement. His proposal centered around the distinctive red spectral line of cadmium as a way to standardize the definition of an angstrom used in spectroscopy.

Fifty-five years after his death, his proposal would be put to use to define the meter. In 1927, the International Conference on Weights and Measures adopted the cadmium red line as the standard for the meter. They defined the meter to be equivalent to 1,553,164.13 wavelengths of cadmium red light.

The meter would be redefined to different atomic spectral lines over time until 1983 when the speed of light would become the meter’s standard.

Babinet’s principle is a principle in optics where the interference pattern formed by shining a light on an opaque body is identical to the interference pattern formed from shining a light through a hole cut of the same size and shape in a screen except for light intensity.

### Notable Science History Events for March 5

#### 1982 – Venera 14 lands on Venus.

The Soviet Venus probe, Venera 14 landed on the surface of Venus. It managed to take soil samples and send back pictures for nearly an hour before being destroyed by the 465 °C, 94 atm atmosphere.

Venera 14 was designed with spring-loaded arms to measure the compressibility of the soil. Unfortunately, when the lens cap from the cameras popped off, it fell right where the soil sampler would strike the ground. Instead of measuring the compressibility of the soil, it measured the compressibility of the lens cap.

#### 1846 – Edouard van Beneden was born.

Beneden was a Belgian cytologist known for discoveries on how chromosomes combine during cell meiosis and that all cells in a species have the same number of chromosomes. Together with Theodor Boveri, he theorized that the egg and sperm cells contribute an equal number of chromosomes to the new cell created during fertilization. Boveri introduced the term centrosome to describe the division center for a cell during cell division.

#### 1837 – Alessandro Volta died.

Volta was an Italian physicist who was a pioneering figure in early electricity research and invented the chemical electric battery. He introduced the concept of electromotive force, or the force required to separate positive and negative charges. His battery was similar to the citrus battery using zinc and copper electrodes separated by an acid.

#### 1827 – Pierre-Simon Laplace died.

Laplace was a French mathematician and physicist who made several contributions to mathematical science. He converted the study of classical mechanics from geometry to calculus. He also introduced Laplace’s equation which is widely used in the study of electromagnetism, quantum mechanics, gravity, fluid dynamics, and thermodynamics.

#### 1794 – Jacques Babinet was born.

#### 1575 – William Oughtred was born.

Oughtred was the English mathematician who is credited with the invention of the slide rule. He was also credited with the introduction of the × symbol for multiplication and the abbreviations for trigonometric functions, sine, and cosine.