1. Exploring Electrical Technology Origins of Electricity & Magnetism (E & M)

2. Origins of E & M ► Before the time of Christ: those who became familiar with the mysterious repulsive and attractive mysterious repulsive and attractive forces of certain materials included forces of certain materials included  Chinese  Greeks ► Lodestone: a magnetic oxide of iron (also known as magnetite) naturally available in the earth, for those who stumbled upon it See also: http://www.phy6.org/earthmag/lodeston.htm

3. Origins of E & M: Chinese ► Chinese: probably 1 st to use lodestone for navigation lodestone for navigation ► According to Timetables of Science  Chinese Book of the devil valley master contains first known reference to lodestone’s alignment with Earth’s magnetic field; here the lodestone is called a “south-pointer” (310-301 BC) Consider the wisdom of this early choice by the Chinese, in contrast to the later idea of Europeans, given what you learned from your experiment today.

4. Origins of E & M: Chinese ► According to Timetables of Science  In China, by 271 AD, the first form of a compass was probably used for finding south  Tseng Kung Liang’s Wu Ching tsung yao (a compendium of important military techniques) describes the magnetized iron “fish” that floats in water and can be used for finding south; about the same time Chinese began applying the compass for navigation, most likely using the iron “fish” (1084 AD)

5. Origins of E & M: Definition of some key terms ► Magnetic field: invisible lines of force along which a magnetized needle aligns itself if allowed to move freely ► Navigation: finding out how to go (plotting a course) to get where one is going (destination) ► Compass: in the magnetic version, relies on a pivoted, magnetized needle and Earth’s magnetic field to provide a reference direction for navigation

6. Origins of E & M: Chinese ► Timetables of Science also cites  Chinese scientist Shen Kuo’s Dream Pool essays that contain the first known reference to the use of a magnetic compass for navigation  Chu Yu’s Pingchow table talk that contains the first mention in Chinese literature of a compass used for seagoing navigation ► What about the geography of China might have made Chinese especially interested in the southerly direction?

7. Origins of E & M: Chinese precede Europeans; Greeks amused ► This brief history suggests that Chinese discovered and may have invented the magnetic compass before Europeans. ► On the other hand, Greeks intermittently intrigued themselves by mysterious powers of “magical” materials, during early days

8. Origins of E & M: Greeks ► Ancient Greeks noticed both  Static (electric) forces  Magnetic forces ► Found lodestone  Mentioned in Greek texts by 800 BC  Claim two possible origins of the word “magnet” ► The province of Magnesia where mined (Lucretius) ► The shepherd Magnes, its discoverer (Pliny the Elder)

9. Origins of E & M: Greeks ► By around 600 BC, engaging interest emerged among Greeks w/Thales of Miletus  Greek mathematician, astron. & philosopher  Gave an interpretation of matter (~ 575 BC): “water is the basis of all things”  Intrigued by 2 mysterious phenomenon ► That magnetite attracts iron ► That rubbed amber attracts a light dry object How good was this early theory? Import to life? Consider also II Peter 3:5. Consider the demonstration as an illustration.

10. Origins of E & M: Greeks ► Greeks were on the trail, but not scientifically yet, nor for applications ► Rather they remained a bit confused, amused and entertained at best

11. Origins of E & M: Compass ► Probably 1 st practical application of magnet ► Apparently 1 st invented by Chinese ► Origin uncertain: China, Italy or Arabia ► 1 st known Western reference to magnetic compass (~1195 AD)  By Alexander Neckham (b. St. Albans, England 1157)  In De naturis rerum (on natural things) Since this work occurred well before the printing press, how accessible and well distributed do you think this work may have been? Why?

12. Origins: Early Understanding of Magnetism ► Promoted by Petrus Peregrinus de Mericourt  A French crusader and engineer  Published Epistola de magnete (letter on the magnet)  Concepts he contributed ► The identity of magnetic poles by Earth analogy ► That magnetic poles remain distinct even after a magnet is crushed ► The observation that unlike poles attract ► That a strong magnet can reverse the polarity of a weak one (try on a nail and sense with a compass)

13. Origins: Early Understanding of Magnetism ► Christopher Columbus: while 1st voyaging to the Americas in 1492, found magnetic compass changes somewhat the direction it points as longitude changes (declination) ► By 1550, Robert Norman (English) had described the magnetic dip (inclination): the increased angle of magnetic field lines with respect to horizontal near the poles Why might he have been one of the first to notice this phenomenon?

14. Summary ► Magnetism and Electricity originally discovered as separate phenomena with special powers ► Lodestone became the basis of a magnetic compass to facilitate navigation ► Peregrenus promoted understanding of magnetism ► Experienced navigators discovered non-ideal aspects of compass performance  Declination  Inclination