to operate above coil, the size of plates being 5x7 inches? A. We do not know that this point has been determined. 3. Would two carbons and one zinc in a battery give better results than a pair. and what should be the thickness of each? A. Two carbons and one ZInC are better than one carbon and one zinc; one fourth of an inch is a good thicknesifor each. 4. How is the length of a spark of an induction coil measured? A. The length of a spark of an induction coil is the dis tance between the

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... s from which the discharge takes place. (42) J. H. asks if a building roofed witb iron is any more liable to be struck by lightning than one built of wood. A. An iron roofed bnilding is no more likely to be struck than one of wood. The iron roofed building is the safer if struck; especially so if tbe roof is well connected with the earth by rods.