From the information you have observed, determine the following:
What rule of magnetism is illustrated by the lines of the iron filings in Step 12?
What rule of magnetism is illustrated by the lines of the iron filings in Step 15?
Why was glass or plastic used to separate the filings from the magnets in the experiments?
Did the glass or plastic stop the passage of the magnetic lines of force?
Did the iron filings almost or completely bridge the open end of the horseshoe magnet?