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<p>The two formulae employed by Coffin give results in very close agreement, and the only question remaining is whether the two closely-agreeing formulae are as accurate when applied to the coil in question as they appear to be. In deriving the formulae the current is supposed to be uniformly distributed over the surface of the cylinder, whereas the coil is actually wound with 661 turns of round wire having a diam. of 0.0634 cm. and insulated by a covering 0.0030 cm. thick. The author shows that the summation formula which takes account of the actual size and position of the wires of the coil gives the true value, and that the current-sheet formula, which is very exact for a current sheet or for a winding of thin s
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<br>Subjects: electromagnetic induction; Electrical instruments and techniques</div>
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