Claude-Louis Berthollet (1748-1822), French doctor and chemist. Berthollet graduated in medicine, but by 1780 his work in the new science of chemistry led to his admission to the French Academy of Sciences. Berthollet supported the theories of Lavoisier, but correctly disagreed with him by proposing that some acids do not contain oxygen. His book Essai de statique chimique (1803) was the first systematic work on chemical physics. He also worked on a wide range of chemicals, as well as dyes and gunpowder. Berthollet was a friend of Napoleon Bonaparte and was made a count (Comte Berthollet), but in 1814 he helped depose Napoleon as Emperor, 'for the good of France'. 19th-century engraving.

At the age of 14, Tycho Brahe was amazed to find out that astronomers could exactly fortell an eclipse of the sun. Determined to study astronomy, he bought a globe and books with his own money.

At the age of 14, Tycho Brahe was amazed to find out that astronomers could exactly fortell an eclipse of the sun. Determined to study astronomy, he bought a globe and books with his own money.

James Bradley (1693-1762), English Astronomer Royal. Bradley is chiefly remembered for his work on stellar parallax and the speed of light. Stellar parallax is the slight shift in the apparent position of stars which is observed when the Earth is at opposite ends of its orbit. Bradley measured this, but discovered it to be larger than could be accounted for by the shift in the Earth alone. The remainder was due to the velocity of the Earth relative to the speed of light; in the frame of reference of a moving Earth, light will necessarily be bent. So observations will be very slightly altered. From this Bradley estimated the speed of light.

James Bradley (1693-1762), English Astronomer Royal. Bradley is chiefly remembered for his work on stellar parallax and the speed of light. Stellar parallax is the slight shift in the apparent position of stars which is observed when the Earth is at opposite ends of its orbit. Bradley measured this, but discovered it to be larger than could be accounted for by the shift in the Earth alone. The remainder was due to the velocity of the Earth relative to the speed of light; in the frame of reference of a moving Earth, light will necessarily be bent. So observations will be very slightly altered. From this Bradley estimated the speed of light.

Color enhanced portrait of William Hunter (1718-1783), Scottish anatomist and physician. Together with his brother, John Hunter, he founded the first school of anatomy in London. His published works included studies on human teeth and the pregnant uterus. New York Academy of Medicine.

Albert Einstein (1879-1955).

Benjamin Franklin (1706-1790), American scientist, inventor and statesman. Franklin showed that lightning is electricity by flying a kite carrying a metal key during a thunderstorm. This led to his invention of the lightning rod to protect buildings from lightning strikes. He also invented fins for swimming, bifocal glasses, a urinary catheter and showed that evaporation cooled objects. In between all this, he also found time to found the USA, help shape the revolution and be a signatory of the Declaration of Independence.

Illustration of Gregor Johann Mendel (1822-1884), Austrian botanist and founder of genetics. Mendel, the abbot of an abbey in Brno, carried out breeding experiments with pea plants. His results revealed the statistical laws of heredity, and he postulated the existence of a unit of heredity that is now called the gene.

Illustration of Thomas Hunt Morgan (1866-1945), US geneticist and Nobel Laureate. Morgan was born in Kentucky, and studied zoology at the State College. He then moved to Johns Hopkins University. His work in genetics is largely remembered for the use of the fruit fly Drosophila melanogaster, and for establishing many ideas in chromosome theory. It was Morgan who proved that the chromosome was the carrier of heredity, and that the chromosome consists of genes. He also discovered crossover (the exchange of genes between chromosomes), and helped produce the first chromosome map. In 1933 he was awarded the Nobel Prize for Physiology or Medicine.

Illustration of Albert Einstein. Einstein was born at Ulm, Germany on March 14, 1879. Encouraged by his father, an electrical engineer, Einstein studied at the Zurich Polytechnic Institute until the age of 21. Shortly afterwards he started working at the Swiss Patent Office. Although famous for his papers on special and general relativity, he won the 1921 Nobel Prize for physics for his work on the photoelectric effect. Einstein died on April 18, 1955 without completing his grand unified Theory of the Fundamental forces, which remains uncompleted by today's theoretical physicists.

Geoffrey Chaucer (1343-1400), was an English author, poet, philosopher, bureaucrat, courtier and diplomat. He is best remembered for his narrative The Canterbury Tales.

Portrait of Geoffrey Chaucer (1343-1400).

English physician John Caius (1510 - 1573).

Ptolemy (87 - 150 AD). A Greek living in Alexandria, Ptolemy extended Hipparchus' theory of the solar system. Ptolemy's system involved at least 80 epicycles to explain the motions of the Sun, the Moon, and the five planets known in his time. He believed the planets and sun to orbit the Earth in the order: Mercury, Venus, Sun, MArs Jupiter, and Saturn. This system became known as the Ptolemaic system. Ptolemy was also a cartographer and geographer, and his maps remained the principal work on the subject until the time of Columbus.

Edmund Halley (1656-1742), English astronomer who discovered Halley's comet.

Polish astronomer Johannes Hevelius (1611-1687) and his wife Elisabetha observing the stars. This is an illustration from Hevelius' book "Machina Coelestis" (Celestial Machine). Hevelius invented ten new constellations, seven of which are still recognized by astronomers. Elisabetha Koopman, Hevelius' second wife and assistant, completed her husband's final project after his death.

Portrait of Nicolaus Copernicus (1473-1543), the Polish astronomer who first claimed that the Universe was centered around the Sun. From 1512, he developed a mathematical model for this heliocentric theory. This system contrasted with the thousand-year-old Earth-centered Ptolemaic system, to which the Roman Catholic church adhered. Copernicus feared persecution and delayed publication of his book, "The Revolution of the Heavenly Spheres," until 1543. The book was banned by the Roman Catholic church from 1616 until 1835.

Portrait of Nicolaus Copernicus (1473-1543), the Polish astronomer who first claimed that the Universe was centered around the Sun. From 1512, he developed a mathematical model for this heliocentric theory. This system contrasted with the thousand-year-old Earth-centered Ptolemaic system, to which the Roman Catholic church adhered. Copernicus feared persecution and delayed publication of his book, "The Revolution of the Heavenly Spheres," until 1543. The book was banned by the Roman Catholic church from 1616 until 1835.

An illustration of Guglielmo Marconi (1874-1937), then aged 21, in his father's garden at Pontecchio, conducting early experiments with a transmitter which produced a spark between two balls, one connected to a metal plate suspended in the air, the other to one in the earth-- showing the receiving apparatus in the background. Marconi was Italian physicist, Nobel Laureate and developer of wireless telegraphy. Marconi came from a wealthy family, and was privately tutored. In 1894 he read about the radio waves of Hertz, and set about applying this theory to sending signals. Making his own instruments, Marconi managed to send messages in morse code over increasingly longer distances. He moved to England in 1898, by then sending signals over 20 miles. In 1901 he reached his crowning achievement, by sending a radio message across the Atlantic Ocean. For this he shared the 1909 Nobel Prize in Physics with Karl Ferdinand Braun, and was given the title Marchese by the Italian Government.