March 21 is Jean Baptiste Fourier’s birthday. Fourier was a French mathematical physicist who is best known for the Fourier series.

The Fourier series is a method to express any general periodic function into an infinite sum of simple sine and cosine expressions. Converting a periodic function into an infinitely long addition problem might seem like complicating matters, but it actually makes a great approximation tool after just a few terms. Each term in the series refines the term before it as a harmonic. The first term gives a general shape to the curve and the second refines it by a rough amount. The third term refines this shape a little more and the fourth tweaks that shape. For most functions, a “close enough” approximation can be reached after five or six terms. This process is used extensively in optics, quantum mechanics, acoustics and electrical engineering. Basically, any study where waves are found.

Fourier was an active voice in the French Revolution and served on his district’s revolutionary committee. Unfortunately, he had a difference of opinion with the resulting government and ended up imprisoned and faced the guillotine during France’s Reign of Terror. He avoided this fate once Robespierre’s government fell and began teaching mathematics at the École Polytechnique in Paris. From there, he joined the Army as a scientific advisor when Napoleon invaded Egypt. While in Egypt, he took part in excavations and helped found and administered the Institut d’Égypte in Cairo. He must have done an impressive job since Napoleon appointed Fourier the Prefect of Grenoble when Fourier returned to France.

Once he returned, he gained notoriety with a treatise on the propagation of heat in a solid body. It was based on the idea that heat flow from one point to another is proportional to the differences between the two points’ temperature. The part that caused controversy was the introduction of what is now known as the Fourier series. Many of the leading mathematicians disagreed with his conclusions and methods. Ultimately, Fourier would be proven correct.

Fourier was also the first to describe what has become known as the “greenhouse effect”. He had seen experiments where materials enclosed between panes of glass would begin to heat up. He described a theory where the atmosphere served to heat the surface of a planet by slowing heat loss back into space.

Fourier continued to publish mathematical papers until his death in 1830 when he tripped and fell down the stairs of his home.

### Notable Science History Events for March 21

#### 1992 – John C. Sheehan died.

Sheehan was an American organic chemist who was the first to synthesize penicillin. He also discovered a compound called 6-aminopenicillanic acid (6-APA) that forms the basic foundation for synthetic penicillins. Sheehan used this to develop ampicillin, a synthetic penicillin taken orally instead of by injection. His inventions allowed for the mass production of these useful antibiotics.

#### 1988 – Patrick Steptoe died.

Steptoe was a British doctor who developed in vitro fertilization with Robert Edwards. Their work would produce the first ‘test tube’ baby in 1978. Edwards would receive the 2010 Nobel Prize in Medicine for their work, but Steptoe was not considered for the Prize because he died prior to the award. The Nobel Prize only goes to living scientists.

#### 1932 – Walter Gilbert was born.

Gilbert is an American biochemist who shares half the 1980 Nobel Prize in Chemistry with Fredrick Sanger for developing methods to find the nucleotide sequence order for nucleic acids. He also developed the equilibrium dialysis technique to determine ion bonding of proteins.

#### 1925 – The State of Tennesee enacts the Butler Act.

The Butler Act went into effect in the state of Tennessee. The Butler Act prohibited the teaching of the theory of evolution in any publicly funded school. This law would be famously tried during the Scopes-Monkey trial. The law would remain in effect until 1967.

#### 1768 – Jean Baptiste Joseph Fourier was born.

#### 1762 – Nicolas Louis de Lacaille died.

Lacaille was a French astronomer who cataloged thousands of southern hemisphere stars and introduced 14 new constellations. He was the first to publish a catalog of stars of the Southern Hemisphere. He also produced a calendar list of eclipses spanning 1800 years.