September 14 is Charles François de Cisternay du Fay’s birthday. Du Fay was a French chemist who made early contributions to the study of electrical charge.
Du Fay discovered there were two types of electric charge. He named these charges after the methods he used to separate them. Vitreous (Latin for glass) electricity is generated when glass is rubbed with fur. Resinous (Latin for resin or amber) electricity is obtained from rubbing amber with silk or paper. He also noticed the different charges would attract each other, but the same kind of charge would repel each other. He developed a theory to explain this behavior where there existed two different fluids. Neutrally charged objects would have equal amounts of both fluids which would neutralize each other. When rubbed, an object would lose one of these fluids and leave an excess of the other.
Today we know these type of electrical ‘fluids’ are actually electrical charges where vitreous is positive charge and resinous is negative charge. These charges are caused when the rubbing forces a transfer of electrons.
Du Fay also noticed he could transfer charges by induction to metals and liquids. He also showed the electrical properties of an object that depended on color were caused by the dye that colored the object and not the color itself. He found glass was an insulator of electrical charge and thread conducts better when wet rather than dry. Most importantly, he discovered two bodies charged with vitreous or two bodies charged with resinous would repel each other and a vitreous charged body would attract a resinous charged body. We know this today as like charges repel, opposites attract.
Notable Science Events for September 14
1952 – Soviet Luna 2 spacecraft ‘lands’ on the Moon.
NASA
The Soviet spacecraft Luna 2 impacted the Moon’s surface. Luna 2 was the second of a series of probes designed to fly to the Moon and crash into the surface. Luna 1 missed the Moon by 5,995 kilometers. Luna 2 did not miss. It would become the first man-made object to reach the surface of the moon.
Luna 2 also confirmed Luna 1’s discovery of the solar wind.
1936 – Ferid Murad was born.
Murad is an American physician who shares the 1998 Nobel Prize in Medicine with Robert F. Furchgott and Louis J. Ignarro for their discoveries involving nitric oxide as a signal molecule for the cardiovascular system. Murad was the first to show nitroglycerin worked as a drug by releasing nitric oxide into the body which caused blood vessels to dilate. Furchgott and Ignarro determined the intermediate chain of events and reactions that cause this effect.
1882 – Georges Leclanché died.
Leclanché was a French electrical engineer who developed one of the first dry cell batteries. The Leclanché cell used an electrolyte of ammonium chloride with terminals made of zinc and manganese dioxide and was the predecessor of the modern battery design used in flashlights and portable electronics.
1849 – Ivan Petrovich Pavlov was born.
National Institutes of Health
Pavlov was a Russian physiologist who is best known for his work on conditioned behavior in an experiment involving dogs and bell ringing before feeding. His initial research was into the physiology of the digestive system of dogs and was collecting saliva for analysis when he noticed the dogs would start to salivate before the food even reached their mouths. Further research showed dogs could be conditioned to show a reflex response to an unrelated stimulus. Although he was known for this research, it was his research into the digestive system that earned him the 1904 Nobel Prize in Medicine.
1712 – Giovanni Domenico Cassini died.
Cassini was an Italian astronomer and mathematician who co-discovered with Robert Hooke the Giant Red Spot on Jupiter. He also discovered four of Saturn’s moons: Iapetus, Rhea, Tethys, and Dione.
The Cassini Division is the name of the dark gap he discovered that divides Saturn’s rings. He suggested the rings were made of small particles rather than a solid mass that was the common belief at the time.
For more about Giovanni Cassini, check out June 8 in Science History.
1698 – Charles François de Cisternay du Fay was born.
1638 – Pierre Vernier died.
Vernier was a French mathematician who introduced the vernier scale for measurements. A vernier is a small movable scale that allows for extra significant figures or more precision in the measurement.
When a measurement is made with a vernier equipped device, the initial digit in the measurement is the last primary fixed rule before the ‘0’ mark on the vernier scale. The next digits are where the mark on the vernier is lined up on the primary fixed rule.