Julius Sumner Miller: Lesson 40 - Adventures in Magnetism

We find in Nature certain stuffs which are magnetic. Fe - Ni - Co are naturally magnetic. And magnetite - an iron ore - is magnetic. In fact -everything is magnetic to some degree - some things more - some less. The reason for this is clear: The primordial origin of magnetic forces lies in the motion of electrons. In some stuffs the magnetic domains are more abundant than in others.
A - How can we make a magnet: Answer: Hold a magnetizable bar - like an iron bar -in the Earth's magnetic meridian. Give it a proper "dip". Now strike it sharply with a hammer... at one end. The bar is - presto! magnetized! A wonderful thing really. We can check this by approaching a compass needle with one end of the bar just magnetized. If the needle is repel led the bar IS magnetized. Only repulsion proves this. Attraction does not! The reason is clear: A bar of magnetic stuff unmagnetized will attract a compass needle. See why?
B - How else can we make a magnet? Answer: Wrap a coil of wire around a magnetic stuff - like an iron rod say. Energize the coil with an electric current. The bar becomes polarized. It is a magnet. This results from the fact that a current-bearing conductor gives rise to a magnetic field. . .discovered by Oersted in 1820.
C - How else can we make a magnet? Stroke a bar of iron - say - with a chunk of magnetite or with another magnet. The polarity of the sample magnetized is governed by the pole last leaving the sample.
D - Problem: We magnetize a sample of stuff - say an iron rod. It has a certain "pole strength". That is to say: it is so strong. Now we break this bar just magnetized. The pieces each become a complete magnet with their own poles. Question: What is the pole strength of each piece? A very good question. HINT: We do work to break the original magnet. THIS energy must play some role somewhere.
E - Problem: We have two identical bars - absolutely identical - or so they look. One however is magnetized - the other is not. How can we determine which is the magnet without any accessories whatsoever? No strings to hang them on - no needles to try - nothing at hand. We are free however to handle both bars with utter freedom. HINT: The influence of a bar magnet is largely concentrated at the ends. Need we say more?
F - Question: Is stainless steel magnetic? Answer: No. And so we ask further: Why?
G - How can we protect a region or a thing from magnetic influence? That is - how can we insulate against magnetism? We explore this with numerous stuffs - Al - Zn - Cu - wood - lucite - and so on. And we find that magnetic insulation is best accomplished by surrounding the thing we wish to protect with a proper thickness of soft iron.
H - We explore the region around an arrangement of bar magnets by
sprinkling iron filings. The forms which come to light are enchanting to see.