Sep 25, 1644: Danish astronomer, Ole Christensen Rømer, was born. Rømer was the first to demonstrate conclusively that light travels at a finite speed. He made measurements of the length of time between eclipses of Jupiter by one of its moons. These observations produced different results depending on the position of the earth in its orbit around the sun. The size of the error was as much as ten minutes on measurements taken a month or two apart. He reasoned that light took longer to travel the greater distance when earth was travelling in its orbit away from Jupiter. This was correct. For some reason, Rømer never made the speed calculation, but others did from his data. The result is within 20 percent of the true value for the speed of light.

Rømer was a polymath and did many things. He was made Chief of Police in Copenhagen. When he took office, his first act was to fire the entire department and start over, in order to eliminate corruption. He developed the first temperature scale for a thermometer using the freezing and boiling points of water. Fahrenheit visited him and improved on Rømer’s design. He invented the first street lights in Copenhagen, and worked to improve the lives of beggars, the poor, and unemployed. He developed building codes, got the water and sewar systems of Copenhagen working properly, and a very long list of other things in the fields of engineering, mechanics, and navigation.

Sep 25, 1725: French military engineer, Nicolas-Joseph Cugnot, was born today. He invented the world’s first fuel-propelled vehicle, a large, heavy, steam-powered tricycle. In 1769 he developed the first vehicle driven by a steam engine — a gun tractor commissioned by the French government. The following year he produced the first mechanically driven “horseless carriage”. His steam tricycle, driven by a steam engine, carried four passengers and was the forerunner of the modern automobile.

Sep 25, 1773: Agostino Marla Bassi de Lodi, an Italian entomologist, botanist and bacteriologist, was born today. He’s known as the father of insect pathology for his pioneering work investigating the cause of transmission of disease in animals. Ten years before Louis Pasteur found disease-causing microorganisms, Bassi showed that a silk worm disease was contagious and could be transmitted naturally by direct contact, from infected food, or experimentally by means of a pin previously sterilized in a flame. The causative agent was later shown to be a fungus that multiplied in and on the body of the insect. This was the first microorganism to be recognized as a contagious agent of animal disease. Thus, the first animal pathogen to be understood was of insects, not humans. In 1844, he believed that “contagion by living organisms” also infected humans with measles, syphilis, and the plague.

Sep 25, 1807: American telegraph pioneer, Alfred Lewis Vail, was born today. Vail was an associate and financial backer of Samuel F. B. Morse in the experimentation that made the telegraph a commercial reality. Vail’s contributions were large. He invented the telegraph key. Vail is responsible for the remarkable efficiency of Morse code by applying the principle that the most frequently sent letters should have the shortest code. Morse code has not been in commercial use since 2000 but is commonly used by radio amateurs because it’s effective and fun. Morse has been in used for over 160 years, longer than any electrical coding scheme.

Sep 25, 1832: American civil engineer and architect, William Le Baron Jenney, was born on this day. His technical innovations were of primary importance in the development of the skyscraper. During the Civil War he served as an engineering officer. By 1868 he was a practicing architect who had designed a Swiss Chalet style home with an innovative open floor plan, years before Frank Lloyd Wright worked with the concept. He was a skilled town planners, but his greatest fame came from his large commercial buildings. His Home Insurance Building in Chicago was one of the first buildings to use a metal skeleton for support.

Sep 25, 1839: German paleontologist, Karl Alfred von Zittel, was born. He proved that the Sahara had not been under water during the Pleistocene Ice Age. A distinguished authority on his subjects and their history, he was a pioneer of evolutionary paleontology and was widely recognized as the leading teacher of paleontology in the 19th century. His five-volume “Handbuch der Paläonologie” was arguably his greatest service to science, and it remains one of the most comprehensive and trustworthy paleontological reference books.

Sep 25, 1843: U.S. inventor of the carpet sweeper, Melville Bissell, was born. At his a crockery shop in Grand Rapids, Michigan, his wife’s health was affected by dust from the packing materials. Out of desperate need for self-preservation, he invented the carpet sweeper. They recognized the sweeper’s marketing possibilities and began to assemble them in a room over the store. The inner workings and cases were made by women working in their homes. Tufts of hog bristles were bound with string, dipped in hot pitch, inserted in brush rollers and then trimmed with scissors. Anna Bissell gathered the parts together in clothes baskets and brought them back to the store for assembly.

Sep 25, 1843: American geologist, Thomas Chrowder Chamberlin, was born. He was known for his “planetesimal hypothesis”. With Forest Ray Moulton in 1904, he proposed that the solar system formed after gas flares were ripped from the sun by the gravitational field of a passing star. The flares then condensed into “planetesimals,” arrayed in a spiral extending from the sun, gradually accumulated material and became the planets we know today. In 1881 he headed the glacier division of the U.S. Geological Survey.

Sep 25, 1846: German meteorologist and climatologist, Wladimir (Peter) Köppen, was born. Best known for his delineation and mapping of the climatic regions of the world, he played a major role in the advancement of climatology and meteorology for more than 70 years. The climate classification system he developed remains popular because it uses easily obtained data (monthly mean temperatures and precipitation) and straightforward, objective criteria. He recognized five principal climate groups: (A) Humid Tropical (winterless climates); (B) Dry (evaporation constantly exceed precipitation); (C) Humid Mid-Latitude with mild winters; (D) Humid Mid-Latitude with severe winters; (E) Polar (summerless climates).

Sep 25, 1866: American geneticist and zoologist, Thomas Hunt Morgan, was born on this day. He’s famous for his experimental research with the fruit fly by which he established the chromosome theory of heredity. He discovered that a number of genetic variations were inherited together and that this was because their controlling genes occurred on the same chromosome. At Columbia University (1904-28), he began his revolutionary genetic investigations of the fruit fly Drosophila melanogaster. Initially skeptical of Gregor Mendel’s research, Morgan performed rigorous experiments which demonstrated that genes were linked in a series on chromosomes and are responsible for identifiable, hereditary traits. In 1910 he discovered sex-linkage in Drosophila, and postulated a connection between eye color in fruit flies and human color blindness. His study of the characteristics inherited by mutants ultimately enabled him to determine the precise behaviour and exact localization of genes. Morgan and his “fly room” colleagues, mapped the relative positions of genes on Drosophila chromosomes. Morgan published his seminal book, The Mechanisms of Mendelian Heredity in 1915. Though this work was not widely accepted initially, Morgan was awarded a Nobel Prize for physiology or medicine in 1933.

Sep 25, 1904: American oceanographer, Columbus O’Donnell Iselin was born on this day. He was director of the Woods Hole Oceanographic Institution in Massachusetts from 1940 to 1950 and from 1956 to 1957. He expanded its facilities 10-fold and made it one of the largest research establishments of its kind in the world. Iselin developed the bathythermograph and other deep-sea instruments responsible for saving ships during WW II. He made major contributions to research on ocean salinity and temperature, acoustics, and the oceanography of the Gulf Stream.

Sep 25, 1974: Scientists first reported that freon gases released from aerosol spray cans were destroying the ozone layer.

Sep 25, 1956: The world’s first transatlantic telephone cable system began operating from Clarenville, Newfoundland to Oban, Scotland. Previous cables had been limited to telegraph transmissions.

Sep 25, 1820: Francois Arago announced that a copper wire between the poles of a voltaic cell, could laterally attract iron filings to itself. His discovery came in the same year that Oersted discovered that an electric current flowing in a wire would deflect a neighbouring compass needle. Arago in the same publication described how he had successfully succeeded in causing permanent magnetism in steel needles laid at right angles to the copper wire. Arago and André-Marie Ampère, discussed and experimented with forming the copper wire into a helix to intensify the magnetizing action. However, it was not until 1825 that the electromagnet in its familiar form was invented by William Sturgeon.