The sudden parting of H and S would produce strong sparking across the gap between them if it were not for the condenser, which consists of a number of tinfoil sheets separated by layers of paraffined paper. All the "odd" sheets are connected with T, all the "even" with T^1. Now, the more rapid the extinction of magnetism in the core after "break" of the primary circuit, the more rapidly will the lines of force collapse, and the more intense will be the induced current in the secondary coil. The condenser diminishes the period of extinction very greatly, while lengthening the period of magnetization after the "make" of the primary current, and so decreasing the strength of the reverse current. TRANSFORMATION OF CURRENT. The difference in the voltage of the primary and secondary currents depends on the length of the windings. If there are 100 turns of wire in the primary, and 100,000 turns in the secondary, the voltage will be increased 1,000 times; so that a 4-volt current is "stepped up" to 4,000 volts. In the largest induction coils the secondary winding absorbs 200-300 miles of wire, and the spark given may be anything up to four feet in length. Such a spark would pierce a glass plate two inches thick. It must not be supposed that an induction coil increases the _amount_ of current given off by a battery. It merely increases its pressure at the expense of its volume--stores up its energy, as it were, until there is enough to do what a low-tension flow could not effect. A fair comparison would be to picture the energy of the low-tension current as the momentum of a number of small pebbles thrown in succession at a door, say 100 a minute. If you went on pelting the door for hours you might make no impression on it, but if you could knead every 100 pebbles into a single stone, and throw these stones one per minute, you would soon break the door in. Any intermittent current can be transformed as regards its intensity. You may either increase its pressure while decreasing its rate of flow, or _amperage_; or decrease its pressure and increase its flow. In the case that we have considered, a continuous battery current is rendered intermittent by a mechanical contrivance. But if the current comes from an "alternating" dynamo--that is, is already intermittent--the contact-breaker is not needed. There will be more to say about transformation of current in later paragraphs. USES OF THE INDUCTION COIL.