Page:Popular Science Monthly Volume 92.djvu/815

 Popular Science Monthly

��tween the rotating and fixed electrodes of the rotary gap. If the studs are set back so that when the gap is the shortest (i.e., when the electrodes are exactly in line) a voltage of 7,500 is required to cause a spark to jump, and if the design is such that a potential of 15,000 volts would force a spark across even when the elec- trodes are farthest apart (the moving studs exactly half-way between the fixed), the conditions illustrated in Fig. 42 will be had. The spark gap is supposed to have the number of studs and the speed chosen so that the electrodes approach and recede 600 times per second. The illustration Fig. 42 shows roughly what will happen in four half-cycles under these conditions. The first time the gap be- comes closest there will not be enough po- tential to break it down, so the spark will be missed. The second time udll produce a spark, since the secondary condenser will just have reached 7,500 volts. The third spark will pass, as will the fourth. These are indicated by shaded portions where the two voltage curves overlap. The fifth and sixth sparking opportuni- ties will be missed, because the condenser voltage will in neither case be high enough to break across the minimum gap length. At the seventh, eighth and ninth oppor- tunity sparks will occur, and the tenth and eleventh will miss. The twelfth, thirteenth and fourteenth will pass, but the fifteenth and sixteenth wall be lost. Thus it is seen that there will be three sparks in each half-cycle, at the distance represented by 1/600 second of time, and that between each group of three sparks there will be an idle interval of 1/200 (3/600) second. If the sparking opportunities do not occur at exactly 1/600 second separa- tion, but slightly less often, there will be two sparks in some half-cycles and three in others.

This will give a fairly complete idea of the rotary gap operating upon the non- synchronous principle. You should go over the details of this type of non- synchronous gap operations until you have firmly in mind the relations of voltage and gap length. The effect of changing various adjustments will be treated next month, when the quenched and rotary synchronous gaps will also be described.

{To be continued.)

��709

IIow to Make an Efficient Weather- proof Goose-Neck

AVERY efl'icient weather-proof goose- neck wall bracket can be easily con- structed as shown in the illustration. It consists of a piece of ,' 2-in. conduit bent

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WOOD BLOCK LOCKNUT

����. pie: PLrtTEL- GUTLEIT BOX e>U5MlNG

��A conduit bent and fitted with pie- plate reflector to make a weather-proof goose-neck

in the shape shown and fastened into the wall with a locknut. The outer end has a wood block or disk attached with a lock- nut and rubber gasket. On the under side of this disk is an inverted pie plate to which the lamp sockets are securely attached. — Chris. Bach, Jr.

��A Temporary Repair for a Slipping Magneto Shaft

ABOUT the most annoying mishap a L driver has to contend with on the road is that of a magneto shaft slipping endways so that the gears will be out of mesh. One cause of this trouble is the pump wheel shearing its pin and allowing the shaft to slip endways and out of mesh with the gears. In order to take the pump off and make the repair it is necessary to remove the starter, and this is entirely too big a job to do on the road.

TIMING GEARJ

COTTER
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Placing a cotter in a magneto shaft to keep it from shifting endways out of gear mesh

The repair may be made in a temporary manner as shown in the illustration. A hole drilled through the shaft just in front of the stuffing box, as shown at A, provides a way for holding the shaft with a cotter. It is then only necessary to time the distributor, and the engine runs the same as before. — P. P. Avery.

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