![ William Gilbert, also known as Gilberd, (24 May 1544 – 30 November
1603) was an English physician, physicist and natural philosopher. He
was an early Copernican, and passionately rejected both the prevailing
Aristotelian philosophy and the Scholastic method of university
teaching. He is remembered today largely for his book De Magnete
(1600), and is credited as one of the originators of the term electricity.
He is regarded by some as the father of electrical engineering or
electricity and magnetism.[1] While today he is generally referred to as
William Gilbert, he also went under the name of William Gilberd. The
latter was used in his and his father's epitaph, the records of the town
of Colchester, and in the Biographical Memoir in De Magnete, as well as
in the name of The Gilberd School in Colchester, named after Gilbert.
A unit of magnetomotive force, also known as magnetic potential, was
named the gilbert in his honour.](https://image.slidesharecdn.com/earthsmagnetism-170624044412/85/Earth-s-magnetism-8-320.jpg)
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Earth's magnetism
- 2. Now weshall try to explain some observable events on the earth’s surface from an understanding of the earth’s interior. We would like to emphasize, however that scientists did not necessarily arrive at these explanations in the same manner. In fact, they used the knowledge gained from studies of these phenomena to build a model of the earth’s structure.
- 3. Do you wantto know about Earth’s Magnetism?
- 4. As earlyas2600B.C., thatChineseknewthat a certainkindof rock, whenshapedintoa rodandallowedtoturnedfreely, pointedina north- southdirection. AncientGreeksdiscovereda certainmineraltheynamedmagneticcould attractiron.
- 5. 1100A.D. thefreelyturningmagnethadbecomeastandardfornavigation. 1400A.D. sailorsknewthattheneedle-shapedmagnet, nowcalleda compass, didnot alwayspointexactlyto thenorthpole. It sometimespointeda littleto theeastor a littleto westof north.
- 6. Do you wantto know about Gilbert’s Experiment?
- 8. William Gilbert,also known as Gilberd, (24 May 1544 – 30 November 1603) was an English physician, physicist and natural philosopher. He was an early Copernican, and passionately rejected both the prevailing Aristotelian philosophy and the Scholastic method of university teaching. He is remembered today largely for his book De Magnete (1600), and is credited as one of the originators of the term electricity. He is regarded by some as the father of electrical engineering or electricity and magnetism.[1] While today he is generally referred to as William Gilbert, he also went under the name of William Gilberd. The latter was used in his and his father's epitaph, the records of the town of Colchester, and in the Biographical Memoir in De Magnete, as well as in the name of The Gilberd School in Colchester, named after Gilbert. A unit of magnetomotive force, also known as magnetic potential, was named the gilbert in his honour.
- 9. In 1600WilliamGilbertpublishedabookentitledDe Magnete whereinheexplainedthebehaviorof themagneticrock. He proposedtheearthitselfwasa hugesphericalmagnetwithits polessituatedalmostat thegeographicpoles.
- 10. Gilbertdiscoveredthatwhena compassisheldoverdifferentpointsof a sphericalmagnet,it behavesinaboutthesamewayas it doeswhenit heldat differentpartsof theearth. Thus,heconcludedthattheearthis a MAGNET. As a magnet,theearthis surroundedby a magneticfieldwhoselinesof forcemeetat the magneticpoles.
- 12. Compassandthemagnetactuallyalignthemselvesto thelineof themagneticforce. Thisalignmentmakesthecompasspointnorth-south. It’sbecausetheearth’smagneticpolesarenotlocatedexactlyat thegeographicpoles. At presentthemagneticnorthpoleislocatedat 75°Nlatitudeand 100°Wlongitude.
- 13. Magneticsouthpoleisat 66°Slatitudeand140°Elongitude. Magneticnorthpoleisonlyabout1900kmawayfromthe geographicnorthpole—a distanceslightlylessthan0.05%of theearth’scircumference. Theanglebywhicha compassneedleturnsslightlyawayfromthe geographicnorthpole, whethereastor westof it, iscalled the magneticdeclination.
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- 15. Endof thecompassormagnetthatpointsnorthis calledthe northseekingpoleor N-pole. Oppositepolesattracts. Therefore,thenorthseekingpolemustbethesouthpoleof the compassor magnet. Endthatpointsthesouthisthesouthseekingpole, o t theS-pole.
- 16. Southseekingpole isactuallythenorthpoleof thecompassor magnet. Thus,whena compassis placedneara magnet,thenorth-seekingpole of thecompassis attractedtothesouth-seekingpole,or theS-poleof themagnet. Horizontalcompassis freetoturnarounda verticalaxisanda horizontalplane. However,if a compasswerefreetoturnaroundinall directionsit shouldnotonlypointnorth-southbutalso tilttoonesidesoalongas it is notat themagneticequator.
- 17. A compassconstructedspecificallytoallowtiltingis calledtilting or dippingcompass. It turnson a horizontalaxisandon a verticalplane. Theangleformedbetweenthedippingneedleandthehorizontal planeis calledthemagneticinclination.
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- 21. Do you wantto know about magnetic field?
- 22. A magneticfield is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field The magnetic field is most commonly defined in terms of the Lorentz force it exerts on moving electric charges. There are two separate but closely related fields to which the name 'magnetic field' can refer: a magnetic B field and a magnetic H field.
- 26. The simplesttheory on the origin of the earth’s magnetism is that the center of the earth is one huge permanent magnet made of iron and nickel. Earth’s core consists mainly of these two mainly materials, these theory seems acceptable at first. Laboratory studies show that iron loses its magnetism at 770°C and nickel at 358°C.
- 28. Another hypothesiswas proposed by P.M.S. Blackett, an English physicist. He claimed that the magnetism of the sun, the stars and the earth was caused by their rotation. He set out to prove his theory by developing a highly sensitive instrument for measuring magnetism, the magnetometer.
- 29. Blackett failed,however, to prove his theory. His report entitled “Negative Experiment”, became widely acclaimed because of the full description of the method he used and the precise measurements he made.
- 31. Do you wantto know about Dynamo Theory?
- 32. Walter Elsasserand Edward Bullard developed a hypothesis that presented the earth as an electromagnet rather than a permanent magnet. They attributed the earth’s magnetism to electric current produced in the earth’s interior, which in turn is continually produced by the movement of the liquid outer core.
- 33. The innerand outer core move with different speeds. It is this difference in speed that is the source of magnetism. This is known as the Dynamo Theory.
- 37. 1940’s, scientistsbecame interested in paleomagnetism, or the history of the earth’s magnetism. Development of instruments for measuring magnetism in rocks together with the refinements made in the techniques for establishing rock ages greatly aided scientists in their study of fossil magnets.
- 38. These arebits of magnetic materials (iron) in rocks which have preserved the magnetism of the earth at the time the rocks were formed. Many rocks contain iron-bearing minerals which are naturally magnetic. Studies of rocks in one place but which were formed at different geologic times reveal varying magnetic directions and strengths.
- 39. One interpretationstates the earth is fixed and it is the magnetic poles which are shifting in position. Another interpretation is that the magnetic poles are fixed and it is the whole earth that moves with respect to these poles. A third interpretation is that the magnetic poles are fixed only the upper layers of the earth are shifting about.
- 40. Fossil rocksalso distinguish between the north and the south pole. There is a strong evidence that the poles of the earth’s field have reversed many times in the past. The dynamo theory presents one possible explanation: the direction of the magnetic field is influenced by the direction of the movement of molten iron in the core.