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Circuit for Jump Spark Switch 64 43 Electromagnetic Trailer 66 44 Diagram of Ruhmkorff Coil Circuit 68 45 Windings of Sections 73 46 Sectional Diagram 74 47 Contact Breaker 75 48 Contact Key 76 49 Fall of Potential Diagram 79 50 Series Arrangement 81 51 Multiple Arrangement 82 52 Leclanche Cell 84 53 Samson Cell 87 54 New Standard Cell 90 55 Edison-Lalande Cell 92 56 Fuller Cell 94 57 Grenet Cell 95

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CHAPTER I.
Introductory Remarks.

The enormous number of fires arising from the use of matches, and the great convenience and freedom from danger of the electric method of gas lighting, are alone sufficient reasons for the issue of these pages.

The veriest tyro in electrical operations knows that electricity will cause a spark, and most persons are aware that the spark possesses considerable deflagratory powers, varying with the character of the spark. In electric gas lighting a spark of the proper character is passed across a jet of gas and ignites it. Sparks can be produced by various means: friction, battery current, induction either galvanic or electro-magnetic, by a Wimshurst or Toepler Holtz machine, or an induction coil operated by a battery. For our purposes we will consider only the latter; the former are rarely used, being uncertain and unwieldy.

Of batteries there are many kinds, and although all will produce sparks, yet for electric gas lighting those made for intermittent work and classed as open circuit cells are to be preferred. Open circuit batteries, which will be fully described in a subsequent chapter, include the Leclanche, and most of the so-called “dry” cells.

If two wires be attached to a cell of battery B, one to the carbon or positive pole and the other to the zinc or negative pole, and their free ends be tapped together, minute sparks at C will be observed each time the wires separate (Fig. 1). If now a coil of insulated wire S be included in the circuit, Fig. 2, upon repeating the make and break of contact, the sparks will be much increased. This arises from induction, each adjacent turn of wire acting upon its neighbor. To better understand the action of induction, we will consider the following examples: Fig. 3. A is a circuit in which is the battery cell B. C is a second circuit lying close to but well insulated from circuit A. G is a galvanometer in which a magnetized needle swings right or left each time a current is passed through a coil of wire encircling it. Now, although there is no battery cell in circuit C, yet the needle will swing each time the circuit A is closed or opened; that is, each time the wire ends are touched together or separated. This swing of course indicates that a current is passing through circuit C, but as there is no battery or other source of electrical energy included in it, it is clear that it arises from the action of the current in circuit A. In point of fact, the needle swings one way when the circuit is closed and the reverse way when it is opened; but the greater swing on opening the circuit indicates the greater strength of the induced current at the moment the current ceases to flow in circuit A. Note that these current impulses are only momentary. In the case of our single coil, Fig. 2, each turn of wire acted upon itself in a similar manner to the circuit A upon circuit C.

An iron rod or bundle of iron wires, P, inserted in the coil, Fig. 4, but carefully insulated from it, will immensely increase the inductive effects and consequently the spark. This arrangement constitutes the simple primary coil used in pull-down or pendant and automatic burners. This spark is often a source of inconvenience; it appears wherever a circuit including similar coils is made and broken. In telegraph apparatus at key and relay contacts it is