pieces is a light laminated field structure consisting of two pole pieces F and G, Fig. 106, and a straight core on top. This core carries both primary and secondary windings. The principle of operation is that of sending magnetic lines alternately in opposite directions through the field structure. It will be seen that the pole extensions S and N are simply a means of carrying the magnetic lines from the main magnet to the laminated field structure, and that they do not change their polarity. In the four- and sixcylinder models each polar extension embraces about 90° of the tunnel.

Path of the Flux.-When the pole N is adjacent to G, Fig. 106, left, the magnetic flux flows in the direction of the arrows through the core of the windings from left to right. Continuing the rotation of the poles until they occupy a vertical position it will be seen that the field of the magnet is shorted through the pole pieces, cutting out the magnetic flux entirely from the core. Passing this point in rotation the pole extension N then comes into a position adjacent to F, causing the magnetic lines to flow once more through the core, but this time in the opposite direction, that is, from right to left. This reversal of direction of the magnetic flux is, of course, a necessary feature in any magneto and is the means of inducing the current in the windings.

In order to render this reversal easy and complete, the path for the magnetic lines is made up of thin iron laminations such as are used also in the construction of the armature in the ordinary magneto. The Splitdorf Co., however, make the claim for the Dixie construction that a point of great efficiency is obtained since the bulk of iron in the stationary field structure is so small, its size being governed entirely by magnetic requirements. The windings are remarkably small, being wound on a core of only 0.75 by 0.5 in., Fig. 106, D. The core is held in place by two screws passing through slots in the projecting ends. One end of each of the two windings is earthed. The open end of the high tension winding terminates in a contact plate P, Fig. 106, D, embedded in a rubber block at the side of the windings. The open end of the primary winding passes through a brass tube which leads to the base of the magneto, and so to the contact breaker, Fig. 107.

In dismantling, this wire is the only electrical connection to be loosened.

The Rocking Field-One of the most important features of the magneto is that the whole of the laminated pole structure, including the windings, can be rocked through several degrees. This rocking is accomplished by turning the timer arm of the circuit

Fig. 107.-Sectional View of Splitdorf "Dixie" Inductor Type Magneto.

breaker in the ordinary way to advance or retard the spark. By means of this positive connection between the field and the circuit breaker it is possible to arrange the instrument to produce the sparks either advanced or retarded at the critical moment when the most magnetic lines are being cut. Hence the magneto has no one point in its spark position when the intensity of the spark is maximum or minimum; it is uniform all the time.

The distributor on the four- and six-cylinder models (Fig. 6) consists of an insulating block with a short spindle at one end of which is a spring brush bearing on the contact quadrant P on the windings. The high-tension current passes from this point to a radial arm on the distributor face and so to the outer terminals of the instrument. A good feature is the shortness of the path for the current from the windings to the terminals. A safety spark gap is included in the high-tension circuit at the base of the windings, and the condenser is located on top.

In the circuit breaker (Fig. 106, C) it will be seen that nothing revolves except the cam attached to the shaft. By this construction it is possible to adjust the contact points while running as the contact bases are stationary. The grounding terminal is insulated on the end of the spring clip which holds the breaker cover in position and as it bears on the center of the cover the ground wire is also stationary while moving the timer arm.

The four- and six-cylinder instruments are identical in every respect except the distributor and timing gears. In the eightand twelve-cylinder models the shape of the rocking field and also the polar extensions are changed so that four sparks can be produced in each revolution. The laminated pole pieces embrace 50° each of the upper half of the tunnel, instead of 90°. In order to obtain the requisite number of magnetic reversals with these pole faces the main polar extensions are in the form of a cross, two ends being of N polarity and two of S.

The New Compound Distributor.-As it is practically impossible to obtain more than six contacts in a flat distributor disk of ordinary construction without a great risk of short-circuits caused by dangerously small electrical hazard distances, a particularly ingenious compound distributor (Fig. 106, E and F) has been designed for the eights and twelves in which the terminals are not arranged in one plane as in the four- and six-cylinder models, but in two parallel planes. In the compound distributor block on the eightcylinder instrument the high-tension current is led through the center of the block from the brush C in contact with the windings to the brush D which bears on the center of the cruciform contact plate S embedded in the distributor box. This plate has no con

nections with any terminals, but is a means of conducting the current in turn to the eight terminals as follows: In operation the plate S becomes "live" by contact with the brush D as before explained. Rotating over the ends of S are the two brushes Al

der.

Fig. 108.-Forms of Dixie Magneto. A-Six Cylinder. B-Eight CylinC-For Twelve Cylinder Engines. D-View with Cover and One Magnet Removed to Show Oscillating Coil and Pole Piece.

and B1 connected respectively to two similar brushes A2 and B2 in the side of the block. The path of the latter brush B2 includes the four contact pieces B connected to the four of the terminals, while the other brush A2 rotates in the path of the terminal plates A connected to the remaining four terminals. Now, since the two

brushes A1 and B1 are arranged 135° apart, it follows that eight sparks will be distributed to their respective terminals in one revolution of the distributor block in equal divisions of time. The timer gear is in the ratio of 2 to 1 so that this magneto runs at engine speed, an unusual feature of an eight-cylinder magneto. On the twelve the distributor gear ratio is 3 to 1, requiring a speed one and one-half times the engine speed.

The distributor for the twelves is identical in every respect except that the contact star at the base of the box is six-pointed instead of four, to supply the twelve terminals which are arranged in two layers, as shown in the external view (Fig. 108, C). By the use of the compound distributor block on the eights and twelves as many as 285 sparks of high intensity can be obtained per second. Owing to this high speed of spark production a double contact breaker having two breaker arms and contact points is used on the twelves.

Constructionally the Dixie magnetos are up to the present high standard of practice. The shaft runs on ball bearings, as shown at Fig. 107, tightly fitting brass side covers inclose the magnets and the whole instrument can be dismantled with no other tool than a screw driver. The magnet itself is in two parts and fits into place without bolting, having semi-circular notches which embrace the shaft bearing. Great accuracy has been used in the manufacture of the rotating pole extensions, the clearance between the ends and the stationary poles being brought down to the workable minimum. An interesting point in connection with the operation of these pole extensions is that end thrust is neutralized by the equal magnetic pull on both ends of the rotor. The compactness of the magnets can be realized from the dimensions which except in the height are practically identical in all models. The common width is 4.125 inches and the total length 8.375 inches. On the twelve the height of the magnet is 7.5 inches, being one inch more than the others so as to provide a stronger magnetic field.

The most popular form of magneto, if one can judge by the numbers of manufacturers using it, is the true high tension type. with the revolving winding, though the low tension type using