Handout #3: Some Important ‘Electrically Charged’ Historical Events:
The Greeks (Thales of Miletus and others) (~600 B.C.E.)
• Thales of Miletus (from 640-610 to c. 548-545 ) BC, son of Examyas of Miletus and Cleobuline, was chief of the”Seven Wise Men” of his time and gained much acclaim by predicting a total eclipse of the sun in May 585 BC. Much of his fame came from introducing geometry from Egypt into Greece, before the time of Euclid, making substantial contributions and communicating the beginnings of many propositions to his successors. Everything we know about him comes from accounts written by others.
• Thales is credited with discovering that amber rubbed with wool or fur attracts light bodies such as pieces of dry leaves or bits of straw, and observing that lodestone attracts iron and other lodestones. None of Thales's manuscripts is known to have survived to modem times.
• Thales also showed the influence of a magnet has to a piece of iron, showing that everything has some “soul” or is “filled with Gods” according to Aristotle's De Anima (On the Soul):
And Thales, according to what is related of him, seems to have regarded the soul as something endowed with the power of motion, if indeed he said that the loadstone has a soul because it moves iron.
William Gilbert (1540-1603 C.E.)
• Studied attractive forces of amber that had been rubbed with animal fur or wool.
• Pivoted a light metal arrow so it turned freely – this allowed him to detect very small attractive forces
• Discovered that diamond, sapphire, amethyst, opal, carbuncle, jet, all produced attractive forces when rubbed. Called them “electrics”, and when rubbed they were called “electrified” or as having gained an “electric charge”.
First electrical friction machine: Otto von Guericke (1602-1686)
• Large ball of sulfur on a crank, rubbed with a hand, produced large electrostatic forces.
• Noticed two types of electrification (now what we call + and -)
• Noticed electrostatic induction (some things would exhibit electrification when brought near (not touching) the charged sulfur)
Stephen Gray (1696-1736), an English electrician
• Discovered that corks placed on the ends of glass tubes would be electrified when the glass was rubbed
- The idea was that there was an electrical ‘fluid’, generated at the point of rubbing, that went everywhere within the materials that were connected. First indication that electricity didn’t have to be entirely static but could move.
- This was not the case with non-electrics (metals), in which the ‘fluid’ moved in at a point and out at another point. The flow took place very quickly in non-electrics, so that it lost its charge altogether. We say that it was ‘discharged’. This occurred when fluid passed from the electric, via the metal, into the Earth, where it was thought to spread out so thinly as to be undetectable.
- This explained why metals were not electrified by rubbing: it just passed right into almost anything the metal touched.
- He put metal on a piece of amber, and through rubbing metal WOULD become electrified – so the idea arose that electric forces were universally present in matter
- A consequence of his work was that materials were divided into “conductors” and “insulators” (from a Latin word for island – because one can wall off electrified objects, making them an island of electricity)
Charles Du Fay (1698-1739), a French chemist
• Saw that pieces of cork touched by a rubbed glass rod repelled each other – same if touched with rubbed resin
• Also noticed that a piece of cork touched by glass rod attracted a piece touched by resin – TWO TYPES of electric charge, which he called vitreous (from Latin for ‘glass’) and resinous (because resin exhibited the property)
Ben Franklin (1705-1790)
• Showed that vitreous and resinous electricity would cancel each other and become neutral, thus he found that the two types of electricity were actually OPPOSITE, not just different.
• Popularized the terms Positive and Negative electricity instead of Vitreous and Resinous. Vitreous = Positive Electricity and Resinous = Negative Electricity.
English physicist William Gilbert (1540-1603)
• Postulated that the Earth was a magnet. - Shaped lodestone into a sphere and looked at the behavior of a compass.
• He used the METHOD OF ANALOGY
• Saw magnetic dip of a compass next to lodestone
• Explanation of how lodestone becomes magnetic: it is organized in the magnetic field of the Earth.
• Gilbert also saw that the compass pointed about 11 degrees East of North in London.
This is magnetic declination, and it VARIES constantly. (Now it is 8 deg. W of N in London)
In 1657, mag. dec. was 0 deg. in London.
• Christopher Columbus first noticed mag. dec. in his voyage of 1492.
• Pointed E of N in Spain, N in mid-atlantic and W of N thereafter
• He didn’t tell crew because they would panic at such a ‘violation’ of natural law