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CORRELATION OF THE PHYSICAL FORCES.
more, if I take an iron bar, and put it inside the coil, so long as there is no electric current circulating round, it has no attraction,—as you will observe if I bring a little iron filings or nails near the iron. But now if I make contact with the battery they are attracted at once. It becomes at once a powerful magnet, so much so that I should not wonder if these magnetic needles on different parts of the table pointed to it. And I will show you by another experiment what an attraction it has. This piece and that piece of iron and many other pieces are now strongly attracted (fig. 52), but as soon as I break
Fig. 52.
contact the power is all gone and they fall. What then can be a better or a stronger proof
