noticeable; in fact, the writer has used temporarily a pair of electro-magnets from a telegraph sounder and obtained spark enough to operate a gas lighting burner.

To produce a long spark which will jump across an air gap, a more complicated form of coil is needed, one which more closely corresponds to the experiment noted in Fig. 3. The simple primary coil has here another coil of finer wire, S, wound on it but carefully insulated from it (Fig. 5). This second coil, or “secondary,” has a vast number of turns of fine wire as compared with the primary, which has only comparatively few turns of coarse wire. A primary coil of 40 feet of No. 14 B. & S. copper wire would be inserted in a secondary coil of perhaps 16,000 feet of No. 36 B. & S. This secondary coil, in fact all the apparatus constituting the induction coil, must be most highly insulated, as the electromotive force of the spark is tremendous, and it would be liable to pierce its way through and into the internal winding and so destroy the apparatus. The circuit in the primary is made and broken either by a hand key or by an automatic contact-breaker at C. With a large coil, the intensity of the spark at G is such that it will jump an air-gap of from one-eighth of an inch to over three feet.[A]

This combination of coils and contact-breaker is generally known as a Ruhmkorff or intensity coil, and is shown in elevation in Fig. 6.

Fig. 6.

CHAPTER II.
Multiple Gas Lighting.

Fig. 7.

As we have already seen how a spark is exhibited at an interrupted contact, the means of its application to gas lighting will be considered. Fig. 7 represents the most generally used kind of electric gas burner or “pendant burner.” Its application is shown in Fig. 8. The wire W from the coil C is attached to the brass insulated collar carrying the contact S. The other wire from coil C and battery B is attached to the gas pipe G. As the burner is also screwed into the gas pipe itself, the circuit would be closed were it not for the gap at A on the burner, caused by the collar carrying the contact C and wire W, being insulated from the burner pillar P. When, however, a pull is given to the burner arm chain so as to cause the end of the spring R to strike contact C in passing, contact is made and broken, and a spark passes which ignites the gas issuing from the burner tip, the gas having previously been turned on. A piece of chain with a metal ball is attached to the burner arm in order to pull it down. In this class of burner there are many different makes differing only in minor details.

Fig. 8.

Fig. 9 shows a form of pendant burner which has no platinum contact, but has a broad lug on the insulated collar which is scraped against by the spiral spring when the arm is pulled down. It will be seen that the lug is not held by an insulated collar on the burner top, but is on the extension of an arm attached to the burner pillar by a large screw and insulating washers. The circuit wire goes under the smaller screw seen on the lower part of the contact arm, this forming a strong and neat form of attachment.

Fig. 9.

Now it has heretofore been necessary to turn on the gas before pulling the chain of a pendant burner, but as this is not always desirable the ratchet burner is made. Fig. 10 shows burner carrying a toothed wheel, which is partly rotated when the arm is pulled down. This wheel is mounted on the stem of a valve which opens or shuts according to the point of rotation, and thus shuts off or admits the gas to flow up to the burner. One pull of the arm turns the gas on; at the same time the wipe spring touches the contact on burner collar, and the gas lights. A second pull and the wheel, rotating, turns off the gas. In all burners of this class a spring is provided to carry the arm up and back into its original position ready for another pull. Some burners do not make contact when the arm flies back, thus saving battery current.

Fig. 10.

Fig. 11.

Fig. 11 is an improved form of burner wherein the movable electrode does not pass through the gas flame, neither do the electrodes come in contact with each other when the gas is being turned off. Reference to the cut will show a pin protruding from the base of the coiled spring electrodes, which pin is so arranged as to come in contact with the short end of the pull-arm. When this pull-arm is pulled down it pushes up this pin, elongating the spiral spring electrode sufficiently to make and break contact at the fixed electrode on the burner collar. This burner can be fitted with a porcelain candle slip if desired to match the imitation candle burners.

Stem Burners.

Objection is sometimes made to the ordinary chain pulls from the fact that they jar the fixtures, and also are liable to bend the fixture branches from the strain used in operating the arm. To overcome these objections the stem style of burner is manufactured (see Fig. 12). This stem, it will be seen, carries a convenient key at the end, which is turned either right or left as in an ordinary gas-cock. The moving contact only makes contact when the gas is being turned on and lighted. When turning it off, the arm is retracted so as not to touch the fixed electrode, thus saving battery current.

Fig. 12.

Fig. 13 is a simple lighting attachment for an Argand burner. The moving lever which carries the pull has a German silver spiral