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HOBBIES AND INVENTIONS

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M A K E A r tific ia l L I G H T N I N Gby John L. Welbourn

EDITOR'S NOTE,.-Tl1is equipment is particulaTlysuited fO T scie'lce c!.us-room demonstrotion.s. At1'10 time 8h~u!d a demonstrati,pn be attempted byone unfamiliar with the apparat'US. Although thegia1lt bTu,sh discharge is harmless to the averageperS07\, a shock from any paTt of the equipmentotheT than the high-freqv.e=y tr,ansjormer wi!!caTTY' wi tI l it seri 1L 6 conse q u~rnce.t to t!le personinvolved. It is sttggested thtw.hen this appaTatusis d~mwn8trated before a group of persons, theybe warned 'JOt to touch the appQ.ratu.8and to statlda respectfld distance [rom. the lo,w-voltage equip-ment.

THE apparatus about to be described iscapable of throwing a spark foul' and ahalf feet long. In. spite of its deadly ap-pearance, this spark is quite harmless. Theoperator may hold a metal rod in his handand let it jUqlP to the end of the rod and runthrough his body to ground, not only withoutharm, but without any sensation of shock.A rather spectacular stunt is to hold onewire leading to an incandescent light, andbring the other end neal' the coil. The lampwill be lighted by the current passing throughthe body and may in a few minutes even be

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W IT H G IA N T O U D IN C O ILburned out. A mysUfying trick is to hold ashort length of neon tube inane's hand, andapproach the coil. Long before there is anysign of a spark jumping to the tube, it willlight with its characteristic glow.Many Interesting experiments can be per-formed from an insulated platform. Sincethe spark jumps to grounded objects, if onestands ana board supported by glass in-sulators (milk bottles will do temporarily)and touches the discharge ball with a metalrod, sparks may be drawn from one's bodyby anyone st.anding on the ground. Caremust be taken not to .draw sparks from thebare skln, as they might cause a blister. Afinger ring, or even a spoon in the mouth,can be used as good contacts from which todraw the spark. A peculiar and weird effectcan be had, when one is so charged, byl'fl.ising the free hand above the head in adarkened room, The person will then be

[Continued on page 136]

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Lightninq With Oudin Coil[Continued from page 95]dimly seen outlined by a purple discharge. Small flameswill dart from the raised hand. hair, and even from thetips of the ears.

Perhaps the most awe-inspiring spectacle is the coil oper-ating under full power in a dark room, Long streamers ofpurple fire dart out in all directions from the discharge ball.emitting at the same time an almost deafening noise. Agrounded wire is now slowly moved towards the dischargeball. The streamers change their direction and snap at thewire. Suddenly a heavy spark bridges the gap. and the airbecomes thick with ozone.Many experiments can he performed with this apparatus,and this short sketch gives an idea of some of them.Before beginning the actual construction of the device,it is well to know something of the principle involved.Briefly, it is this: as the frequency of an alternating, highvoltage current rises, it loses many of its normal charac-teristics. At extremely high frequencies it is almost atotally different kind of, electricity. It produces no sensa-tion of the shock when taken through the body, becauseas the frequency becomes higher, the path of travel be-comes closer to the surface. At extremely high frequenciesthis path of travel is so close to the surface that it doesnot touch the nerves. This is known as "skin affect," Ithas a tendancy to diffuse off the conductor into the air,causing the beautiful brush discharges often seen on insulated

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The condenser is made from glass plates, sheets of tinfoil and copper ribbon for tab connections. The glassplates can be bought from a photographer already cut 8xlOinches and are preferable to window glass because theyare free from bubbles and other imperfections. To cleanthem they should be soaked in hot water and then scouredto remove the emulsion.To make the condenser, 132 plates will be required. Itrnight be well to have a few extra in case some are brokenor Drove defective. Sixty of the cleaned plates are nowcovered in the center on both sides with heavy tin foilcut 6x8 inches. This tin foil may be purchased fromwholesale hardware dealers in rolls a foot wide. As isreadily seen, 40 feet will be needed. 1 it cannot be obtainedin this form, a florist might be able to supply it in sheets.To fix the tin foil in place, the plates are heated in anoven, rubbed with a cake of beeswax, and the tin-foil sheetpressed 011 the center so as to leave a margin of one inchon each edge. Both sides of the plates are covered in thismanner. Any ridges or wrinkles in the foil should bepressed out by rubbing gently from the center with a wadof cloth. Copper strips Y s of an inch wide and three incheslong are soldered to the upper left hand corner of eachsheet of tin-foil after which the condenser is ready forassembling.First a plate without tin foil is taken. then a plate pre-pared with the foil is placed on top of it, then anotherclean one is placed on top of the prepared plate. Theseplates are stacked together until five of the prepared platesha ve been used. A clean plate is then placed On top of thepile to act as a cover. The unit is then bound with frictiontape to prevent the plates from separating during the in-

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Lightning With Oudin Coil[Continued from page 137]the secondary coil with a flat spiral of copper or brassr-ibbon about the base to act as the pr irna ry. Because itdeals with high frequency electricity, no meta1 core isnecessary. The cylinder for the secondary is 53 incheshigh and 15 inches in diameter. It is constructed withoutthe use of nails throughout for nails will cause consider-able loss in current due to br-ush leakage. The cylinder isformed on three plywood discs 14:Vz inches in diameterfrcm mounting board or strips of wood 0-inch wide, ~ -inchthick and 53 inches long. The strips are placed side byside and as close together as possible. When the entirecircumference has been covered you should have a solid,well constructed, wooden cyl irider, It should now be shel-Jacked and covered with a layer of wrapping paper. Thisserves to remove the rough edges left by the strips.

The winding on the secondary consists of 700 turns ofNo. 22 D. C. C. copper magnet wire, with the turns spaced14 to the inch. This will amount to about 2.670 feet or 5.2pounds of wire. To wind the coil pass a metal rod throughthe cylinder and mount it between two saw-horses. Beforewinding' the wire on the cylinder, glue a band of one inchcopper ribbon around the cylinder, one inch from the topand another placed three inches from the bottom. Thebands should not meet, a space of about one inch being leftbetween ends. Solder one end of the wire to the top bandand start winding. The spacing' between turns may beohta ined by winding heavy cord alongside of the wire.

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Lightning Oudin Coilith(Continued from '{J4ge150]is automotive high tension wire; that from the condensershould be special, heavily insulated neon sign cable, asshould that also from the spark gap. GREAT CAREMUST BE TAKEN NEVER TO TOUCH THE LOWFREQUENCY TRANSFORMER. The condenser whencharged will retain a considerable quantity of electricityfor days, so it is well to "short" the connections for asecond (with a well insulated metal rod) before touchingthem. The grounded connections may be of braided ribbonor other heavy un insulated wire connected to a water pipe.'This ground should be a water pipe, l1eVe'y a gas pipe. Underno circumstances should the coil be operated unless thisground is established.The coil is now ready to be set, in operation. Clip thewires from the condenser and the spark gap to convenientturns of the primary of the high frequency transformer,start the spark gap motor, and turn on the power. A loudcrackling noise should be heard and streamers of fire seendarting from the discharge ball. Vary the number andposition of the turns used in the primary of the high fre-quency transformer arrd perhaps alter the capacity of thecondenser until maximum output is obtained. Be sure thatall power is shut off when these ad] ustments are made, anddischarge the condensers as mentioned above before touch-ing anything metallic.