LECTURE ON ELECTRICITY.

Thames Star, Volume XLVII, Issue 10343, 28 September 1912, Page 2 (Supplement)

LECTURE ON ELECTRICITY.

Magnetic Effect—We now turn to the magnetic eiiect of an electric current. •

Electricity and Magnetism although, different, are very closely allied to eachi other. We can have electricity without magnetism, wdien it is in the form of stationary or static charge on, a body or conductor and we can have magnetism without electricity.

Lodestone (experiment). L have here a piece of lodestone or, magnetic it is a natural magnet onginaLy found in a place called Magnesia, m Ajsia- Mimpr, from whioh it derives its name of magnet, and, is known- is i the magnetic oxide oi" iron. It L->s the property bi attracting' sniau pieces oi lion; and iron niings, ax.a ili it v/ere suspendea from vie cencrt so tiiat ie could move ireeiy, one» mi would point to the north, and ■ vie other to the soutli, and, these enus w.ould be oa,lled tiie ivlortli and Soatu poles oi the magnet reapectiveiy. iifxpenment magnet). This alao is a magnet, but what is termed an artificial magnet. It has exactly the same properties as the natural mtiguet," but is a great deal stronger and its magnets somewhat

more permanent. j&cperunen.t — two bar magn,ets, illustrating, attraction and repulsion —this is tile true test oi; magnetism. A magnet -viU attract iron at both ends, but oii'ly when, both pieces are magnetised ca.n we get repulsion, and then, only when w,e bring their like poles together.

The Molecular theory of Magnetism. —ilia this theojy all the molecules take up position so that they neutralize each other thus we 'have no free magnetism. But on bringing tliem under the iniHuence of another magnet the molecules form into iine. with thoir n,orth poles facing one dir I e.ction, thus making the bar into aj.l--paren,tly one large magnet having free magnetion of opposite polarity

at the cads.Ekperimenit —Mr. Tempest raade a 6inch nail into a magnet, but on taking it aws.y magaetion ceased.

The reason why this is the case is that soft iron being very ductile and flexible, a® soon as the magnetising force is taken! away the molecules nearly all twist back into their ov-

iginal positions. But with hand steel this is not the case, the motecules are closer together, and owing to the greater friction between

them,- a. greater magnetic force

required to turn them into line, but when tliis force is removed, they re-

main in their njew position and only

slialdp blows or heating the bar to re heat, will cause the molecules to go back again to their original position. That is why hard steel is always used for permanent'magnets. Magmetic Effect of an Electric Ourrent—l have shown that we can have magnetism without electricity, I will now show you that when a current of electricity flows through a conductor, it has or sets) up a; magnetic field around it. Mr Tempest here illustrated his remarks, by experimenting with a< single wire, large coil and bad magnet horseshoe magnet and solenoid.